Tecnical aplicacion1 abb

Technical Application Papers No.1
Low voltage selectivity with ABB
circuit-breakers

1
Index
A theoretical outline of
selectivity
Problems and requirements for the coordination of
the protections......................................................... 2
Main definitions
Selectivity................................................................. 3
Total discrimination (total selectivity)....................... 3
Partial discrimination (partial selectivity).................. 3
Overload zone – Short-circuit zone.......................... 4
Real currents circulating in the circuit-breakers....... 5
Selectivity techniques
Time-current selectivity............................................ 7
Current selectivity..................................................... 8
Time selectivity......................................................... 9
Energy selectivity................................................... 10
Zone selectivity...................................................... 11
How to obtain selectivity with
ABB circuit-breakers
Types of ABB circuit-breakers............................... 12
MCB Miniature Circuit-Breakers
Supply-side S200 / Load-side S200...................... 13
Supply-side S800D / Load-side S200.................... 13
MCCB-MCB Selectivity
Supply-side XT1-XT2-XT3-XT4-T4 / Load-side
MCB....................................................................... 14
Supply-side T5-T6-T7 / Load-side MCB................ 15
Low voltage selectivity with ABB circuit-breakers
Technical Application Papers
MCCB-MCCB Selectivity
Current selectivity................................................... 16
Time selectivity....................................................... 17
Energy selectivity................................................... 18
Zone selectivity (T4L-T5L-T6L)............................... 19
ACB-MCCB Selectivity
Traditional solution................................................. 25
Zone selectivity between Emax 2 and Tmax.......... 26
ACB-ACB Selectivity
Time selectivity....................................................... 28
Zone selectivity between Emax 2 .......................... 29
Directional time selectivity...................................... 32
Directional zone selectivity..................................... 34
Appendix A:
MV/LV selectivity.................................................... 40
Appendix B:
General considerations regarding residual current
selectivity................................................................ 43
Appendix C:
Example of LV/LV selectivity study........................ 45
Appendix D:
Further considerations regarding the real currents
circulating in the circuit-breakers........................... 48
Glossary ................................................................ 52
COVER • CONTACT INFO

2 Low voltage selectivity with ABB circuit-breakers
A theoretical outline of selectivity
Problems and requirements for the
coordination of the protections
Selection of the protection system of the electrical instal-
lation is fundamental both to guarantee correct economi-
cal and functional service of the whole installation and
to reduce the problems caused by abnormal service
conditions or actual faults to a minimum.
Within the sphere of this analysis, the coordination
between the various devices dedicated to protection of
sections of installation or specific components is studied
in order to:
– guarantee safety of the installation and of people in all
cases;
– rapidly identify and exclude just the area involved in the
problem, without indiscriminate trips which reduce the
availability of energy in areas not involved in the fault;
– reduce the effects of the fault on other integral parts
of the installation (reduction in the voltage value, and
loss of stability in rotating machines);
– reduce the stress on components and damage to the
area involved;
– guarantee service continuity with good quality power
supply voltage;
– guarantee adequate support in the case of malfunction
of the protection delegated to opening;
– provide the personnel in charge of maintenance and
the management system with the information needed
to restore service to the rest of the network as rapidly
as possible and with the least interference;
– achieve a good compromise between reliability, sim-
plicity and cost-effectiveness.
In detail, a good protection system must be able to:
– perceive what has happened and where, discriminating
between abnormal but tolerable situations and fault
situations within its zone of competence, avoiding
unwanted trips which cause unjustified stoppage of a
sound part of the installation;
– act as rapidly as possible to limit the damage (destruc-
tion, accelerated ageing, etc.), safeguarding power
supply continuity and stability.
The solutions come from a compromise between these
two antithetic requirements – precise identification of the
fault and rapid tripping - and are defined according to
which requirement is privileged.
For example, in the case where it is more important to
prevent unwanted trips, an indirect protection system is
generally preferred, based on interlocks and data trans-
mission between different devices which locally measure
the electrical values, whereas speeds and limitation of
the destructive effects of the short-circuit require direct
action systems with with protection releases integrated
directly in the devices. In low voltage systems for primary
and secondary distribution, the latter solution is normally
preferred.
The Italian Standard CEI 64-8 “Electrical user installa-
tions with rated voltage below 1000 V in alternating cur-
rent and 1500 V in direct current” regarding low voltage
installations, under Part 5 “Selection and installation of
the electrical components”, gives the following definition
of discrimination:
“Selectivity between protection devices against
overcurrents (536.1)
When several protection devices are placed in series and
when the service needs justify it, their operating charac-
teristics must be selected so as to disconnect only the
part of the installation where the fault is.”
Moreover, in the comments, the following is added:
“The operating situations which require selectivity are
defined by the customer or by the designer of the in-
stallation.”
The Standard therefore states that the operating charac-
teristics must be selected so as to have selectivity, when
the service needs justify this.
In general, designing a selective installation not only
means realising a “state-of-the-art” project, but also
designing a good installation which does, in fact, respond
to the customer’s requirements, not simply to the aspects
of the Standards.
COVER • INDEX • CONTACT INFO

3Low voltage selectivity with ABB circuit-breakers
Atheoreticaloutlineofselectivity
Main definitions
Selectivity
The definition of selectivity is given by the IEC 60947-1
Standard “Low voltage equipment - Part 1: General rules
for low voltage equipment”
Over-current discrimination:
co-ordination of the operating characteristics of two or
more over-current protective devices such that, on the
incidence of over-currents within stated limits, the device
intended to operate within these limits does so, while the
other(s) does (do) not.
Where by overcurrent a current of a higher value than
the rated current is intended, due to any cause (overload,
short-circuit, etc.).
There is therefore selectivity between two circuit-
breakers in series when, for an overcurrent which passes
through both, the load-side circuit-breaker opens thereby
protecting the circuit, whereas the supply-side one re-
mains closed guaranteeing power supply to the rest of
the installation.
The definitions of total selectivity and partial selectiv-
ity are, on the other hand, given in Part 2 of the same
Standard IEC 60947-2 “Low voltage Equipment - Part
2: Circuit-breakers”
Total discrimination (total selectivity)
Over-current discrimination where, in the presence of two
over-current protective devices in series, the protective
device on the load side effects the protection without
causing the other protective device to operate.
Partial discrimination (partial selectivity)
Over-current discrimination where, in the presence of
two over-current protective devices in series, the protec-
tive device on the load side effects the protection up to
a given level of over-current, without causing the other
protective device to operate .
One can speak of total selectivity when there is selectiv-
ity for any overcurrent value possible in the installation.
Between a pair of circuit-breakers, one speaks of total
selectivity when there is selectivity up to the lesser of the
Icu values of the two circuit-breakers, since the maximum
prospective short-circuit current of the installation will in
any case be less or equal to the smallest of the Icu values
of the two circuit-breakers.
One talks about partial selectivity when there is only
selectivity up to a certain Is current value (ultimate
selectivity value). If the current exceeds this value, se-
lectivity between the two circuit-breakers will no longer
be guaranteed.
Between a pair of circuit-breakers, one speaks about
partial selectivity when there is selectivity up to a certain
Is value below the Icu values of the two circuit-breakers.
If the maximum prospective short-circuit current of the
installation is lower than or equal to the Is selectivity
value, one can still speak of total selectivity.
Example
The following two circuit-breakers are considered:
On the supply side XT4N250 TMA100 (Icu=36kA)
On the load side S200M C40 (Icu=15kA)
From the “Coordination Tables” publication it can be seen that there
is total selectivity (T) between the two circuit-breakers.
This means that there is selectivity up to 15kA, i.e. the
lower of the two Icu values.
Obviously, the maximum possible short-circuit current at the point
of installation of the S294 C 100 circuit-breaker will be less than
or equal to 15kA.
Now the following two circuit-breakers are considered:
On the supply side XT4N250 TMA80 (Icu=36kA)
On the load side S200M C40 (Icu=15kA)
TM, M
Supply
side
Version
Release
Iu [A]
In [A]
25
32
40
50
63
32 40 50 63
250
80 100 125
7.5
T
T
T
T
T
T
T
T
T
T
B,C,N,S,H,L,V
XT4
Icu [kA]Charact.
C
Load-side
S200M
* Value valid with magnetic only circuit-breaker on the supply side
XT4N 250 TMA80
S 200M C40
Tmax XT4 - S200M @ 400/415 V
15
5
5*
5
5
7.5
6.5
5*
* *
From the “Coordination Tables” publication it can be seen that
the selectivity value is Is=6.5kA between the two circuit-breakers.
This means that, if the maximum prospective short-circuit current on
the load-side of the S200M C40 circuit-breaker is less than 6.5kA,
there will be total selectivity, whereas if the short-circuit current has
a higher value, there will be partial selectivity, i.e. only for the faults
with a current below 6.5kA, whereas for faults between 6.5 and 15
kA non-tripping of the supply-side circuit-breaker is not guaranteed.

Overload zone – Short-circuit zone By “short-circuit zone” one means the ranges of current
values, and therefore the relative part of the trip curves
of the circuit-breaker, which are 8-10 times higher than
the rated current of the circuit-breaker.
This is the zone in which the magnetic protection for
thermomagnetic releases or protections S, D and I for
electronic releases are normally called on to intervene.
These current values usually correspond to a fault on the
supply circuit. This event is most unlikely than a simple
overload.
For the purposes of the selectivity analysis made in this
publication, the concepts of “overload zone” and “short-
circuit zone” are introduced.
By “overload zone” one means the ranges of current
values, and therefore the relative part of the circuit-
breaker trip curves coming between the rated current of
the circuit-breaker itself and 8-10 times this value.
This is the zone in which the thermal protection for
thermomagnetic releases and protection L for electronic
releases are normally called on to intervene.
These currents usually correspond to a circuit where a
load results to be overloaded. This event is likely to occur
more frequently than a real fault.
0.1kA 1kA 10kA
104s
103s
102s
10s
1s
10-1s
10-2s
0.1kA 1kA 10kA
104s
103s
102s
10s
1s
10-1s
10-2s
Overload Zone = In ÷ 8-10In Short-circuit Zone = > 8-10In
Main definitions

tA
tB
IA IB
IB IA
tA
tB
IA=IB
tA
tB
IA=IB+Iloads
IA=(IB+Iloads)/n
IA=IB
A
B
A
B
A
B
Real currents circulating in the circuit-
breakers
When the time-current curves of two circuit-breakers
are compared, one is often led to assess the trip times
of the two devices as if they were passed through by
the same current.
This consideration is only true when, between the two
circuit-breakers placed in series, there are no other
shunts, i.e. there is a single incoming and a single
outgoing feeder which insist on the same node.
When, on the other hand, there are several supply-side
circuit-breakers which insist on the same busbar or
several outgoing feeders on the load side, the currents
which pass through the apparatus can be even consi-
derably different.
With regard to the real currents circulating in the circuit-
breakers, the three main cases which can be considered
are as follows:
- a single circuit-breaker on the supply side of a single
circuit-breaker on the load side (passed through by the
same current)
- a single circuit-breaker on the supply side of several
circuit-breakers on the load side (supply-side circuit-
breaker passed through by a current higher than that
of the load-side circuit-breaker)
- two or more circuit-breakers on the supply side and
several circuit-breakers on the load side.
Where:
IB
is the overcurrent which passes through circuit-breaker B
IA
is the overcurrent which passes through circuit-breaker A
Iloads
is the sum of the currents which, during normal operation, is consumed by the loads (excluding B) supplied by the supply-side
circuit-breaker A. This sum can, if necessary, be corrected with suitable contemporaneity and use factors
n is the number of circuit-breakers placed in parallel on the power supply side.
* These formulas do not take into account the different phase displacement of the currents or any asymmetry of the circuit; the first two formulas are
however conservative and the third one is acceptable when the two supply circuits are equal.

This section describes the different selectivity techniques and their area of application.
In the overload zone with the protections considerd, time-current type selectivity is usually realised.
In the short-circuit zone with the protections considerd, various selectivity techniques can be used. In particular,
the following will be illustrated in the paragraphs below:
current selectivity
time selectivity
energy selectivity
zone selectivity.
After an initial theoretical description of the different selectivity techniques, the selectivity technique which can be
used appropriately for the different types of circuit-breakers will then be analysed.

Time-current selectivity
In general, the protections against overload have a
definite time characteristic, whether they are made by
means of a thermal release or by means of function L of
an electronic release.
A definite time characteristic is intended as a trip cha-
racteristic where, as the current increases, the trip time
of the circuit-breaker decreases.
When there are protections with characteristics of this
type, the selectivity technique used is time-current se-
lectivity.
Time-current selectivity makes trip selectivity by adju-
sting the protections so that the load-side protection, for
all possible overcurrent values, trips more rapidly than
the supply-side circuit-breaker.
When the trip times of the two circuit-breakers are
analysed, it is necessary to consider:
- the tolerances over the thresholds and trip times
- the real currents circulating in the circuit-breakers.
Operatively speaking
With regard to the tolerances, ABB SACE makes the trip curves of their releases available in the technical catalogues and in the DOCWin
software. In particular, in the curve module of the DOCWin software, the curves of both the electronic and thermomagnetic releases include
the tolerances. A release trip is therefore shown by two curves, one which indicates the highest trip times (top curve), and the other which
indicates the most rapid trip times (bottom curve).
For a correct analysis of selectivity, the worst conditions must be considered, i.e.:
- the supply-side circuit-breaker trips according to its own bottom curve
- the load-side circuit-breaker trips according to its own top curve
With regard to the real currents circulating in the circuit-breakers:
- if the two circuit-breakers are passed through by the same current, it is sufficient for there to be no overlapping between the curve of
the supply-side circuit-breaker and the curve of the load-side circuit-breaker;
- if the two circuit-breakers are passed through by different currents, it is necessary to select a series of significant points on the time
current curves and check that the trip times of the supply-side protection are always higher than the corresponding times of the load
side protection.
1.05 x I1 of the supply-side circuit-breaker
Assuming IA
=1.05xI1, with reference to what has been said about
the real currents which circulate in the circuit-breakers, the IB
current
is obtained on the load side.
The trip times of the two devices are obtained from the time-current
curves.
1.20XI3 (or I2)
of the load-side circuit-breaker
Assuming IB
= 1.20XI3 (or I2), the IA
current is obtained in the same
way on the supply side and, from the time-current curves, the trip
times of the two devices are obtained.
If the following is true for both the points considered:
tA
>tB
then selectivity in the overload zone is guaranteed.
1 1.05 is the value for minimum definite non-intervention dictated by the Standard (IEC60947-2). For some types of circuit-breakers this value could vary
(see the technical catalogue for further information).
2 1.2 is the value for maximum definite intervention for protection against short-circuit dictated by the Standard (IEC60947-2). For some types of circuit-
breakers this value could be lower (see the technical catalogue for further information).
A
B
In particular, in the case of circuit-breakers equipped with electronic releases, since the trend of the curves is at I2
t=const, to carry out
the check correctly, it is sufficient to examine two current values:
1.05 x I11
of the supply-side circuit-breaker (value below which the supply-side protection never intervenes)
1.20XI3 (or I2)2
of the load-side circuit-breaker (value above which the load-side protection certainly trips with the protections against
short-circuit)
Time-current Selectivity
0.1kA 1kA 10kA 100kA
A
B
103s
102s
10s
1s
10-1s
0.1s
1s
10s
100s
1E3s
A
B
Time-current Selectivity
In the figure at the side an absorption of current from other loads has been
assumed

Current selectivity
This type of selectivity is based on the observation that
the closer the fault point is to the power supply of the
installation, the higher the short-circuit current is. It is
therefore possible to discriminate the zone the fault
occurred in by setting the instantaneous protections to
different current values.
Total selectivity can normally be achieved in specific
cases only where the fault current is not high and where
there is a component with high impedance interposed
between the two protections (transformer, very long
cable or a cable with reduced cross-section, etc.) and
therefore a great difference between the short-circuit
current values.
This type of coordination is therefore used above all in the
distribution terminal (low rated current and short-circuit
current values, and high impedance of the connection
cables). The time-current trip curves of the devices are
normally used for this study.
It is intrinsically fast (instantaneous), easy to realise and
economical.
However:
– the ultimate selectivity current is usually low and
therefore selectivity is often only partial;
– the setting level of the protections against overcur-
rents rises rapidly;
– redundancy of the protections, which guarantees
elimination of the fault (rapidly) in the case of one
of them not operating, is not possible.
It is a type of selectivity which can also be made between
circuit-breakers of the same size and without protection
against delayed short-circuit (S).
The ultimate selectivity value which can be obtained is equal to
the instantaneous trip threshold of the supply-side protection less
any tolerance.
Is = I3minA
Note
This selectivity limit, linked to the magnetic threshold of the supply-side circuit-
breaker, is exceeded in all cases where energy type selectivity is realised.
If the settings indicated for energy selectivity are respected for the com-
binations of circuit-breakers with an energy selectivity value given in the
coordination tables published by ABB, the selectivity limit to be taken into
consideration is the one given in the tables and not the one which can be
obtained using the formula given above.
– The protection against short-circuit of supply-side circuit-breaker A will be set to a value which means
it does not trip for faults which occur on the load side of protection B. (In the example in the figure I3minA
> 1kA)
– The protection of load-side circuit-breaker B will be set so as not to trip for faults which occur on its
load side. (In the example in the figure I3MaxB
< 1kA)
Obviously the setting of the protections must take into account the real currents circulating in the circuit-
breakers.
A
B
Cable
3kA
1kA
Current Selectivity
0.1kA 1kA 10kA
A
B
Is
103s
102s
10s
1s
10-1s
10-2s

Time selectivity
This type of selectivity is an evolution of the previous one.
In this type of coordination, apart from the trip threshold
in terms of current, a trip time is also defined: a certain
current value will make the protections trip after a defined
time delay, suitable for allowing any protections placed
closer to the fault to trip, excluding the area which is the
seat of the fault.
The setting strategy is therefore to progressively incre-
ase the current thresholds and the trip delays as one
gets closer to the power supply sources (level of setting
directly correlated to the hierarchical level).
The delayed trip thresholds must take into account the
tolerances of the two protection devices and the effective
currents which circulate in them.
The difference between the delays set for the protections
in series must take into account the fault detection and
elimination times of the device on the load side and of
the inertia time (overshoot) of the device on the supply
side (time interval during which the protection can trip
even when the phenomenon is over).
As in the case of current selectivity, the study is made by
comparing the time-current trip curves of the protection
devices.
Generally this type of coordination:
- is easy to study and realise;
- is not very costly with regard to the protection sy-
stem;
- allows even high selectivity limit values to be obtai-
ned (if Icw is high);
- allows redundancy of the protection functions.
However:
- the trip times and energy levels let through by
the protections, especially by those close to the
sources, are high.
It is a type of selectivity which can also be made between
circuit-breakers of the same size, equipped with electro-
nic releases with delayed protection against short-circuit.
The protections against short-circuit of the two circuit-breakers will be set:
- with the I2 trip thresholds against delayed short-circuit adjusted so as not to create trip overlapping,
taking into consideration the tolerances and the real currents circulating in the circuit-breakers.
- with t2 trip times adjusted so that the load-side circuit-breaker B extinguishes the fault whereas the
supply-side circuit-breaker A, still in the timing phase, manages to “see” the extinction of the current
and therefore remains closed.
The ultimate selectivity limit which is obtained is equal:
– to the instantaneous trip threshold of the supply-side protection,
if this function is enabled, less any tolerance:
Is = I3minA
– to the value of Icw for supply-side air circuit-breakers when the
instantaneous protection function is set to OFF.
Note
These selectivity limits are exceeded in all the cases where energy type
selectivity is realised.
If the settings indicated for energy selectivity are respected for the com-
binations of circuit-breakers with an energy selectivity value given in the
coordination tables published by ABB, the selectivity limit to be taken into
consideration is the one given in the tables and not the one which can be
obtained from the considerations made in this paragraph. 0.1kA 1kA 10kA 100kA
Time Selectivity
A
B
Is
103s
102s
10s
1s
10-1s
10-2s
104s
A
B

Energy selectivity
Coordination of energy type is a particular type of selec-
tivity which exploits the current-limiting characteristics
of moulded-case circuit-breakers. It is pointed out that
a current-limiting circuit-breaker is a circuit-breaker with
a break-time short enough to prevent the short-circuit
current reaching its otherwise attainable peak value”
(IEC 60947-2).
In practice, all the ABB SACE moulded-case circuit-
breakers of the Tmax series, the miniature circuit-break-
ers and the E1.2L air current-limiting circuit-breaker have
more or less marked current-limiting characteristics.
Under short-circuit conditions, these circuit-breakers
are extremely fast (trip times in the region of a few mil-
liseconds) and open when there is a strong asymmetrical
component. It is therefore not possible to use the time-
current trip curves of the circuit-breakers, obtained with
symmetrical sinusoidal types of wave forms, for the
coordination study.
The phenomena are mainly dynamic (therefore propor-
tional to the square of the instantaneous current value)
and are heavily dependent on the interaction between the
two pieces of apparatus in series. Therefore the energy
selectivity values cannot be determined by the end user.
The manufacturers make tables, slide-rules and calcu-
lation programmes available where the ultimate current
selectivity values of Is under short-circuit between dif-
ferent combinations of circuit-breakers are given. These
values are defined by theoretically integrating the results
of tests carried out in compliance with what is indicated
in Annex A of the IEC 60947-2 Standard.
The Is ultimate selectivity limit obtained is the one given in the tables which ABB SACE makes available to the customer.
The protections against short-circuit of the two circuit-breakers must respect the conditions given below.
- Supply-side release of thermomagnetic type
the magnetic trip thresholds must be such so as not to create trip overlapping, taking into consideration the tolerances
and the real currents circulating in the circuit-breakers;
the magnetic threshold of the supply-side circuit-breaker must be equal to or higher than10xIn or set to the maximum
value when it is adjustable.
- Supply-side release of electronic type
any protections against delayed short-circuit S must be adjusted following the same indications as time selectivity;
the instantaneous protection function I of the supply-side circuit-breakers must be set to off
I3=OFF
B
Supply
side
XT4
N,S,H,L,V
Release
In [A] 160 250
TM, M
Version
Load side
XT2
N
S
TM 160
In [A]
8
10
12.5
16
20
25
32
40
50
63
80
100
125
160
85
85
85
70
85
85
85
70
85
85
85
70
55
50*
85
85
85
70
55
50
50*
50*
85
85
85
70
55
50
50*
50*
85
85
85
70
55
50
50*
50*
50*
85
85
85
70
55
50
50
50
50
A
H
V
L
80 100 125 160 200 225 250
55* 55
50* 50 50
50 50 50 5050* 50 50
50 50 50 5050* 50* 50
50 50 50 5050* 50* 50
50 50 50 5050* 50* 50*
50* 50 50 5050* 50*
50*
* Value valid with magnetic only circuit-breaker on the supply side
Energy Selectivity
B A
1E5s
1E4s
1E3s
100s
10s
1s
0.1s
1E-2s
1E-2kA 0.1kA 1kA 10kA 100kA
Is
A
B

Zone selectivity
This type of coordination is an evolution of time coor-
dination.
In general, zone selectivity is made by means of dialogue
between the current measuring devices which, once
the setting threshold has been detected as having been
exceeded, allows just the fault zone to be identified cor-
rectly and the power supply to it to be cut off.
It can be realised in two ways:
– the measuring devices send the information linked
to the current setting threshold having been exceeded
to a supervision system and the latter identifies which
protection has to intervene;
– when there are current values higher than their setting,
each protection sends a lock signal by means of a direct
connection or a bus to the hierarchically higher level pro-
tection (on the supply side in relation to the power flow
direction) and, before intervening, checks that a similar
lock signal has not arrived from the load-side protection.
In this way only the protection immediately on the supply
side of the fault intervenes.
The second case allows definitely shorter trip times.
Compared with coordination of the time type, the need
to increase the intentional delay as one moves towards
the power supply source is no longer necessary. The
delay can be reduced to the time needed to exclude
the presence of a possible lock signal coming from the
load-side protection.
This is a type of selectivity suitable for radial networks
and, when associated with the directional protection,
also suitable for meshed networks.
Compared with coordination of time type, zone selec-
tivity allows:
- reduction of the trip times (these can be lower than
hundred milliseconds);
- reduction both of the damage caused by the fault and
of interferences to the power supply system;
- reduction of the thermal and dynamic stresses on the
components of the installation;
- a very high number of selectivity levels to be obtained.
However:
- it is more burdensome both in terms of cost and of
complexity of the installation
- it requires an auxiliary supply.
This solution is therefore mainly used in systems with
high rated current and short-circuit current values, with
safety and service continuity requirements which are
both binding: in particular, there are often examples of lo-
gical selectivity in primary distribution switchgear imme-
diately to the load side of transformers and generators.
A remains closed
B opens
A opens
B remains closed
A
B
Fault current
Lock signal
A
B
Fault current
Lock signal
This is a type of selectivity which can be realised:
- between Emax 2 air circuit-breakers equipped with Ekip Touch and Ekip Hi-Touch releases.
The ultimate selectivity limit which can be obtained is equal to the Icw Is = Icw
- between Tmax T4L,T5L and T6L moulded-case circuit-breakers equipped with PR223 EF releases.
The ultimate selectivity limit which can be obtained is 100kA Is = 100kA
Then, by means of the S51/P1 contact module, it is possible to make a chain of zone selectivity between Tmax and Emax. It is also
possible to realise a selectivity chain including ABB MV protections.
The operating principle of zone selectivity between ABB circuit-breakers is as follows:
When there are current values higher than their setting, each protection sends a lock signal by means of a direct connection or a bus to
the hierarchically higher level protection (on the supply side in relation to the power flow direction) and, before intervening, checks that
a similar lock signal has not arrived from the load-side protection. In this way only the protection immediately to the supply side of the
fault intervenes.

How to obtain selectivity with ABB circuit-breakers
MCB
Miniature Circuit-Breakers
These are the System Pro-M Compact series of circuit-
breakers.
They are equipped with thermomagnetic releases whose
trip characteristics conform to the IEC60898 Standard
and to the DIN VDE 0660 Standard.
These circuit-breakers have the breaking capacity (Icu)
complying with the Standard IEC 60947-2 and the energy
selectivity limits refer to this Standard.
ACB
Air Circuit-Breakers
These are the Emax 2 series of circuit-breakers.
They can be equipped with electronic releases.
The most advanced electronic releases of the Emax
series are the Ekip touch/G touch, which allows zone
selectivity to be realised, and the Ekip Hi-Touch/G
Hi-Touch which, apart from zone selectivity, also allows
directional zone selectivity to be realised.
MCCB
Moulded-Case Circuit-Breakers
These are the Tmax and Tmax XTseries of circuit-breakers.
They can be equipped with thermomagnetic or electronic
releases.
The most advanced electronic release of the Tmax series
is the PR223EF which allows zone selectivity to be reali-
sed between moulded-case circuit-breakers.
Types of ABB circuit-breakers
How to obtain selectivity with the different types of ABB
circuit-breakers will be analysed in details in the next
chapters.
Each chapter is dedicated to a particular combination
of circuit-breakers and to the methods to realise selec-
tivity between them.This pubblication gives indications
for rapid selection of the circuit-breaker adjustments in
order to obtain selectivity.
These indications about adjustments of the releases
are generally valid and are used for rapid selection of
the settings.
For specific combinations of circuit-breakers and for
specific installation conditions, ABB SACE may provide
indications which do not respect the rules given in this
document.
Here is a short description of the different types of ABB
circuit-breakers taken into consideration in this publi-
cation.

Supply-side S200 / Load-side S200
Only current type selectivity can be required between two circuit-breakers of the S200 series.
In particular, the following prescriptions are valid:
- In the overload zone, the load-side circuit-breaker must trip more rapidly than the supply-side circuit-breaker, taking into consideration
the tolerances and the effective currents circulating in the circuit-breakers.
- In the short-circuit zone given that the following are:
I3minA
the lowest magnetic threshold of the supply-side circuit-breaker A
I3MaxB
the highest magnetic threshold of the load-side circuit-breaker B
IkB
the maximum prospective short-circuit current on the load side of B
These are circuit-breakers with a thermomagnetic rele-
ase and therefore neither time selectivity let alone zone
selectivity is possible.
The two selectivity techniques which can be used are
This is assuming that the magnetic trip th-
resholds of the supply-side circuit-breaker and
of the load-side circuit-breaker do not create
trip overlapping, taking into consideration the
real currents circulating in the circuit-breakers.
If the following relationships are verified:
I3minA
> IkB
I3MaxB
< IkB
one can talk about total selectivity.
Otherwise there will be partial selectivity and
the ultimate selectivity limit will be:
Is = I3minA
Supply-side S800D / Load-side S200
Between the S800 curve D circuit-breakers on the supply side and
the circuit-breakers of the S200 series on the load side, ABB SACE
provides selectivity tables which give the values of energy selectivity.
In particular, for the values of the tables to be considered valid, the
following prescriptions are valid:
- in the overload zone, the load-side circuit-breaker must trip
more rapidly than the supply-side circuit-breaker, taking into
consideration the tolerances and the real currents circulating in
the circuit-breakers.
- in the short-circuit zone, the lower magnetic trip threshold
of the supply-side circuit-breaker and the upper magnetic trip
threshold of the load-side circuit-breaker must be such so as
not to create trip overlapping, taking into consideration the real
currents circulating in the circuit-breakers.
current selectivity and energy selectivity. Depending on
the type of MCB on the supply side, either one or the
other can be realised.
A
B
Cable
IkB
Energy selectivity between S200 D40 and S200 C10
0.1kA 1kA 10kA0.1kA
Is
A
B
103s
102s
10s
1s
10-1s
10-2s
Energy selectivity between S800 D100 and S200L C25
0.1kA 1kA 10kA0.1kA
Is
B
A
103s
102s
10s
1s
10-1s
10-2s
MCB-MCB Selectivity
A
B
HowtoobtainselectivitywithABBcircuit-breakers
The Is ultimate selectivity limit which is obtained is the one given
in the tables which ABB SACE makes available to the customer
S800S
D
63
S200
In [A]
8
10
13
16
20
25
32
40
Icu [kA]
80 100 125
50
40 50
T
2.8
2.8
2.5
2.5
2.3
2.3
3.9
3.9
3.3
3.3
3
2.4
B
A
Supply
side
Characteristic
Load side
C 10
0.8
0.8
0.8
0.8
0.8
0.8
1.1
1.1
1.1
1.1
1.1
1.1
0.9
1.4
1.4
1.4
1.4
1.3
1.3
1.1
1.1
1.9
1.9
3
2.4
T
5.6
5.6
4.7
3.7
3.7
4.7

Supply-side XT1 XT2 XT3 XT4 T4 / Load-side MCB
In the “Coordination Tables” publication, there are tables with circuit-breakers of the TMax XT1, XT2,
XT3, XT4 and T4 series on the supply side of the modular circuit-breakers of the S200 and S800
series. The energy selectivity values given are valid once the conditions described below are verified.
The case where selectivity is required between a
moulded-case circuit-breaker on the supply side and a
modular circuit-breaker on the load side is now analysed.
The Is ultimate selectivity limit which is obtained is the one given
in the SOC 2 web tool.
Overload zone
In the overload zone, the load-side circuit-breaker must trip more
rapidly than the supply-side circuit-breaker, taking into consi-
deration the tolerances and the real currents circulating in the
circuit-breakers.
Short-circuit zone
Supply-side circuit-breaker of thermomagnetic type
The magnetic trip threshold must be:
- higher than or equal to 10xIn when the magnetic threshold is
fixed (TMD)
- set to the maximum value when the magnetic threshold is
adjustable (TMA)
- such so as not to create trip overlapping with the load-side
circuit-breaker, taking into consideration the tolerances and
the real currents circulating in the circuit-breakers.
Is
Selectivity between XT4 250 Ekip In100 and S200P C50
1E5s
1E4s
1E3s
100s
10s
1s
0.1s
1E-2s
A
B
MCCB-MCB Selectivity
In this case, thanks to the different size of the two circuit-
breakers, it is always possible to obtain energy selectivity.
A
B
XT4
B,C,N,S,H,L,V
63
S200P
In [A]
13
16
20
25
32
40
160 250
EL
40
B
A
Supply
side
Release
Load side
C 10/15
Version
I [kA]cu
T
T
T
T
T
T
100
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
TT
50
63
Supply-side circuit-breaker of electronic type
The instantaneous protection function I must be set to OFF
I3=OFF
The I2 current threshold of function S, less any tolerance, must be
adjusted so as not to create trip overlapping with the upper ma-
gnetic threshold of the load-side circuit-breaker I3MaxB
, taking into
consideration the real currents circulating in the circuit-breakers.

With regard to the t2 trip time of function S:
t2A
≥ 100ms both with I2
t=const as well with t=const

Supply-side T5-T6-T7 / Load-side MCB
With the Tmax T5, T6 and T7 moulded-case circuit-breakers and the modular circuit-breakers on the load
side, there is always total selectivity if the conditions described below are verified.
Selectivity between T5N400 PR221In320 and S204 D63
0.1kA 1kA 10kA
B
A
103s
102s
10s
1s
10-1s
10-2s
104s
Is
Overload zone
In the overload zone, the load-side circuit-breaker must trip more
rapidly than the supply-side circuit-breaker, taking into consi-
deration the tolerances and the real currents circulating in the
circuit-breakers.
Short-circuit zone
fixed (TMD)
adjustable (TMA)
The instantaneous protection function I must be set to OFF
I3=OFF
The Is ultimate selectivity limit is the lesser between the breaking capacity of the supply-side circuit-breaker and the breaking capacity
of the load-side circuit-breaker.
With reference to the example given in the figure above
S204D63 Icu=15kA
T5N400 Icu = 36kA
there is therefore Is = 15kA
The I2 current threshold of function S, less any tolerance, must be
adjusted so as not to create trip overlapping with the upper ma-
gnetic threshold of the load-side circuit-breaker I3MaxB
, taking into
consideration the real currents circulating in the circuit-breakers.

With regard to trip time t2 of function S:
t2A
≥ 100ms both with I2
t=const as well with t=const
A
B

Current selectivity
Looking for current selectivity between moulded-case circuit-breakers may be necessary when there are circuit-breakers of the same
size which do not have energy selectivity values in the tables.
In any case, only low selectivity values in the order of a maximum of 10 times the In rated current of the release on the supply side can
be obtained.
To obtain the current type of selectivity, the following prescriptions must be respected:
In the overload zone, the load-side circuit-breaker must trip more rapidly than the supply-side circuit-breaker, taking into consideration
the tolerances and the effective currents circulating in the circuit-breakers.
The case where selectivity is required between two
moulded-case circuit-breakers is now analysed. In this
case, different techniques can be used to obtain selec-
tivity between the circuit-breakers:
current selectivity
for combinations of circuit-breakers which do not have
an energy selectivity value when an element with high
impedance is placed between the two
time selectivity
for combinations of circuit-breakers which do not have
an energy selectivity value and the supply-side circuit-
breaker is equipped with an electronic release
energy selectivity
for the combinations given in the “Coordination Tables”
publication
zone selectivity
for Tmax circuit-breakers equipped with PR223EF re-
leases
If the following relationships are true:
I3minA
> IkB
I3MaxB
< IkB
one can speak of total selectivity.
Otherwise there will be partial selectivity and the
ultimate selectivity limit will be:
Is = I3minA
This is assuming that the magnetic trip thresholds of
the supply-side circuit-breaker and of the load-side
circuit-breaker do not create trip overlapping, taking
into consideration the real currents circulating in the
circuit-breakers.
In the short-circuit zone given that the following are:
I3minA
the lower magnetic threshold of the supply-side circuit-breaker A
I3MaxB
the upper magnetic threshold of the load-side circuit-breaker B
IkB
the maximum prospective short-circuit current on the load side of
B
A
B
Cable
IkB
A
1E5s
1E4s
1E3s
100s
10s
1s
0.1s
1E-2s
B
Current selectivity between XT4N250 TMA250
and XT4M160 TMA80
Is

Time selectivity
Looking for current selectivity between moulded-case circuit-breakers may be necessary when there
are circuit-breakers of the same size which do not have energy selectivity values in the tables and the
supply-side circuit-breaker is equipped with an electronic release with function S (XT2-XT4-T4-T5-T6-T7).
In any case, only low selectivity values in the order of a maximum of 10-12 times the rated uninterrupted
current Iu of the supply-side circuit-breaker can be obtained.
To obtain the time type of selectivity, the following prescriptions must be respected:
In the overload zone, the load-side circuit-breaker must trip more rapidly than the supply-side circuit-
breaker, taking into consideration the tolerances and the real currents circulating in the circuit-breakers.
t2 times set
MCCB on the supply side t2A
=200 t2A
=200 t2A
=400
MCCB on the load side t2B
=50 t2B
=100 t2B
=200
Note
The indications about the adjustments of the releases are valid in general and useful for a rapid choice of setting guaranteing selectivity. For specific
combinations of circuit-breakers and for specific installation conditions, ABB SACE may provide indications which do not respect the rules given in
this document, but however able to ensure selectivity.
The ultimate selectivity limit is equal to the istantaneus trip threshold I3 of the upstream circuit-breaker minus the tollerance
Is = I3minA
In the short-circuit zone
- the I2A
current threshold of function S of the supply-side
circuit-breaker must be adjusted so as not to create trip over-
lapping with the current threshold of the protection against
short-circuit (I3 or I2) of the load-side circuit-breaker, taking
into consideration the tolerances and the real currents circu-
lating in the circuit-breakers
- with regard to trip time t2 of function S, the settings of the
MCCBs on the supply side are indicated below according to
the setting/type of MCCB on the load side:
when the I2A
threshold of the supply-side circuit-breaker
is higher than an instantaneous protection of the load-side
circuit-breaker (magnetic, I3=ON or self-protection) the fol-
lowing is valid:
t2A
≥ 150ms if I2
t =const
t2A
≥ 100ms if t =const
when the I2A
threshold of the supply-side circuit-breaker is only
higher than the I2B
threshold of the load-side circuit-breaker,
by using curves with the same characteristics, the following
is valid:
t2A
- tolerance ≥ t2B
+ tolerance + 50ms
1E5s
1E4s
1E3s
100s
10s
1s
0.1s
1E-2s
A
Time selectivity between two T4
B
Is
This relationship must be respected when, through the dialogue or the Ekip connect software, electronic settings are used. In the
more frequent case - use of the available settings through dip-switches - the values given in the following tables must be complied
with:
A
B

Energy selectivity
ABB SACE makes selectivity tables available to the customer which provide the energy selectivity values
at 415V between the possible combinations of moulded-case circuit-breakers.
Since the moulded-case circuit-breakers can be equipped with thermomagnetic and electronic releases
which are both adjustable, it is necessary for the user to carry out some checks in order to obtain selec-
tivity up to the short-circuit current value given in the tables.
In the overload zone, the load-side circuit-breaker must trip more rapidly than the supply-side circuit-
breaker, taking into consideration the tolerances and the real currents circulating in the circuit-breakers.
Note: The indications about the adjustments of the releases are valid in general and useful for a rapid choice of setting guaranteing selectivity. For
specific combinations of circuit-breakers and for specific installation conditions, ABB SACE may provide indications which do not respect the rules
given in this document, but however able to ensure sectivity.
The Is ultimate selectivity limit obtained is the one given in the
“Coordination Tables” publication.
Iu [A]
N,S,H,L
T6
MCCB - Tmax T5 @ 400/415 V
T7
S,H,L,V(1)
TM, M EL EL
630 1600
400
630
400
630
TM
EL
N,
S,
H,
L,
V
T5
In [A]
320
400
500
320
400
630
30
30
30
630 800(2)
1000(2)
1250 1600
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
800
30
30
30
30
800
630
30
30
30
630
800
30
30
30
30
30
800
1000
30
30
30
30
30
30
1000
800 1000 1250
Supply side
Versions
Release
Load side
t2 times set
MCCB on the supply side t2A
=200 t2A
=200 t2A
=400
=50 t2B
=100 t2B
=20 0
This relationships must be respected when, through the dialogue or the Ekip Connect software, electronic settings are used. In the
more frequent case - use of the available settings through dip-switches - the values given in the following tables must be complied
with:
(XT1-XT2-XT3-XT4-T4-T5-T6)
fixed (TMD)
adjustable (TMA).
the effective currents circulating in the circuit-breakers.
(XT2-XT4-T4-T5-T6-T7)
- the instantaneous protection function I must be set to OFF
I3=OFF
- trip threshold I2A
of the supply-side circuit-breaker must be
adjusted so as not to create trip overlapping with the trip
threshold of the protection against short-circuit (I3 or I2) of
the load-side circuit-breaker, taking into consideration the
tolerances and the real currents circulating in the circuit-
breakers
- with regard to trip time t2 of function S, the settings of the
MCCBs on the supply side are indicated below according to
the setting/type of MCCB on the load side:
when the I2A
lowing is valid:
t2A
≥ 150ms if I2
t =const
t2A
≥ 100ms if t =const
when the I2A
threshold of the supply-side circuit-breaker is
only higher than threshold I2B
of the load-side circuit-breaker,
by using curves with the same characteristics, the following
is valid:
t2A
- tolerance ≥ t2B
+ tolerance + 50ms
Energy selectivity between thermomagnetic MCCB
A
0.1kA 1kA 10kA
B
Is
103s
102s
10s
1s
10-1s
10-2s
A
Energy selectivity between electronic MCCB
0.1kA 1kA 10kA
B
Is
103s
102s
10s
1s
10-1s
10-2s
A
B
(1)
Available only with Iu ≤ 1250 A
(2)
Value valid only for PR232/P,
PR331/P and PR332/P trip units

Zone selectivity (T4L-T5L-T6L)
By means of the new PR223EF electronic release, it is possible to
realise zone selectivity between moulded-case circuit-breakers of
the Tmax T4L, T5L and T6L series.
The PR223EF implements the new EF protection function, ca-
pable of detecting the short-circuit at its onset. This is thanks to
“predicting” the fault, based on analysis of the trend of the current
derivative in relation to the time, di(t)/dt vs i(t).
If the EF protection is enabled, it intervenes for faults of considera-
ble size, replacing the I protection function against instantaneous
short-circuit when there is an auxiliary power supply.
Between PR223EF releases, zone selectivity is implemented simul-
taneously on functions S, G and EF. It is carried out by means of an
interlocking protocol (Interlocking, IL), guaranteed by a couple of
shielded twisted pair cables for modbus RS485 which connect the
circuit-breakers equipped with the PR223EF (ask ABB for further
information about cable type).
In the case of a short-circuit, the circuit-breaker immediately to the
supply side sends a lock signal to the hierarchically higher level
protection by means of the bus and, before trippping, checks that
a similar lock signal has not come from the load-side protection.
System integrity is controlled by a monitoring function: in the case
of a short-circuit, if a fault is found in the interlocking system, the
EF protection function trips (with trip times in the order of tens of
ms), but zone selectivity is not guaranteed.
Furthermore, if the load-side circuit-breaker does not manage to
trip, it asks the supply-side circuit-breaker for help and the latter
opens even if it does not detect the fault (SOS function).
A 24Vdc auxiliary power supply is required for operation of the EF
protection and zone selectivity.
The ultimate selectivity limit which can be obtained is 100kA
Is=100kA
All the protection functions can be programmed remotely, exploi-
ting the dialogue function on the release, or locally by means of
the PR010/T, which can be connected to a serial port on the front
of the PR223EF.
One of the main advantages in using zone selectivity between
MCCBs is the reduction in size of the circuit-breakers it makes
possible.
In fact, in looking for selectivity between moulded-case circuit-
breakers with the classic techniques, it is often necessary to incre-
ase the size of the supply-side circuit-breakers to obtain selectivity
limits congruous with the short-circuit current of the installation.
By means of suitably cabled PR223EF releases, it is possible to
obtain 100kA of selectivity even between two circuit-breakers of
the same size.
An example is given below (see pages 22 and 23) of how, by me-
ans of zone selectivity between moulded-case circuit-breakers, a
reduction in sizes and a considerable reduction in the peak current
and specific energy let through by the circuit-breakers is possible,
whilst still maintaining total selectivity.
More info about PR223EF can be found on document
1SDC007405G0201.
Interlock configuration
Each release is characterised by:
- an input destined for connection with the release on the supply
side “Uplink”
- an output destined for connection with the release on the load
side “Downlink”
Each of the two can be configured in two ways: PP (point-point)
or MP (multi-point) according to the installation condition the
releases are in.
The main configurations are given below:
Uplink: PP/MP
Downlink: PP/MP
PR223EF
MP PP
MPMPMP
PR223EFPR223EFPR223EF
PR223EF
MP
MPMPMP
PR223EFPP
PP
PR223EF
PR223EF

The main parameters, characteristic of the release, are:
Trip delayed Enabling this parameter introduces a trip delay in the case when, on the load side of a release, smaller sized
Tmax or modular circuit-breakers are installed. The aim of this parameter is to obtain selectivity with the
other devices on the load side not equipped with PR223EF.
This parameter is only enabled in the circuit-breakers which have the device outside the zone selectivity
chain on the load side.
EF enable/disable Enabling/disabling protection EF.
If protection EF is enabled:
the presence of Vaux leads to automatic exclusion of function I and enabling of protection EF,
the lack of Vaux leads to exclusion of protection EF and to the return of function I (if enabled).
100 kA Ultimate selectivity limit which can be obtained with the PR223EF suitably cabled and supplied with power.
16 Maximum number of releases which can be connected to the BUS of a level.
1000 meters Maximum overall length of the connection cable. Cabling the different releases is carried out as in the classic
“Bus topology” (see figure).
UPUPUP
PR223EF
Down
= max 1000 m
Cable RS485

Zone selectivity between Tmax
0.1kA 1kA 10kA
B AC
103s
102s
10s
1s
10-1s
10-2s
104s
A
B
C
Trip delayed ON
PR221DS
PR223EF
PR223EF
Indications about the settings
To obtain total selectivity, both in the case of overload and short-circuit, using the PR223EF releases suitably cabled and supplied with
power, making the following selections and the following settings between the various circuit-breakers is recommended:
- Trip delayed
By enabling this parameter on the releases which have a circuit-
breaker directly on the load side not equipped with PR223EF,
selectivity is obtained with the Tmax of a smaller size or the MCBs
placed on the load side.
Overload
- Check there is no trip overlapping of protection functions L
(against overload), taking into consideration the tolerances and
Short-circuit
- No trip overlapping of the I2 current thresholds of function S,
taking into consideration the tolerances and the real currents
circulating in the circuit-breakers.
- Trip time t2
Adjusted so as to realise time selectivity with any load-side
circuit-breaker placed outside the zone selectivity chain.
Between the circuit-breakers equipped with PR223EF and in-
terlocked with each other, if A is the supply-side circuit-breaker
and B the load-side circuit-breaker, the following must be valid:
t2A ≥ t2B.
When possible, it is advisable to look for time type selectivity as
well between the interlocked circuit-breakers so as to guarantee
partial selectivity in case the auxiliary power supply is lost.
- Instantaneous protection function I
This protection function is automatically disabled when function
EF is enabled and there is an auxiliary power supply. Its settings
are therefore only of importance in the case of losing Vaux.

V = 400 V
Ik = 95 kAU
L
LLL
Switchboard A
Switchboard B
QF1
E2.2H800 EKIP TOUCH In800
WC1
6x(1x400)+2x(1x240)+1G400
Ib = 740 A
Iz = 1050 A
L = 17m
PVC
QF1
E2.2H/MS
QF2
T6L630 PR222DS-LSI In630
QS2
T6D630
IkA=74 kA
QF3
XT4L250 EKIP LSI In250
L1
In = 200 A
QF4
XT4H250 EKIP LSI In250
QF5
QF6
L2
In = 200 A
L3
In = 170 A
L4
In = 170 A
IkA=54.5 kA
WC2
6x(1x300)+2x(1x150)+1G300
Ib = 540 A
Iz = 682 A
L = 25 m
PVC
WC3
3x(1x150)+1x(1x95)+1G95
Ib = 200 A
Iz = 275 A
L = 10m
PVC
WC4
3x(1x95)+1x(1x50)+1G50
Ib = 200 A
Iz = 207 A
L = 40m
PVC
WC5
3x(1x95)+1x(1x50)+1G50
Ib = 170 A
Iz = 207 A
L = 60m
PVC
WC6
3x(1x95)+1x(1x50)+1G50
Ib = 170 A
Iz = 207 A
L = 30m
PVC
Example of application
In the following example a comparison between an installation where selectivity is implemented with traditional techniques and the same
installation with selectivity ensured by EFDP system is given.
Traditional installation
The choice of the protection devices shall be carried out above all making reference to the rated currents of the loads and to the short-
circuit current of the busbars. Besides, this choice is influenced by the search for selectivity realized through traditional techniques, whose
values can be found in the SOC2 ABB web page.
The short-circuit current at the busbars of switchboard B (IkB
=54.5kA) influences the choice of the protection devices and imposes the
use XT4H250 circuit-breakers on the outgoing feeders.
In order to guarantee selectivity, the circuit-breaker (QF2) on the supply side of switchboard B and installed in switchboard A must be
T6L 630 type.
The busbar of switchboard A is characterized by a short-circuit current value IkA
=74kA: this affects deeply the choice of the upstream
protection device which, independent of the rated current, shall be an Emax 2 circuit-breaker and precisely an Emax E2.2H, therefore
able to guarantee selectivity towards the apparatus on the load side.
Each switchboard has got as main device a switch-disconnector, which shall be protected against short-circuit and overload by the
circuit-breaker on the supply side. Generally speaking, in order to guarantee protection, it is necessary to use a switch-disconnector in
the version derived from the circuit-breaker on the supply side.
Therefore it is evident that the selectivity requirements condition deeply the choice of the protection devices and direct it towards diffe-
rentiated sizes according to the location of the circuit-breakers in the installation.

V = 400 V
Ik = 95 kAU
L
LLL
Switchboard A
Switchboard B
QF1
T6L800 PR223EF In800
WC1
6x(1x400)+2x(1x240)+1G400
Ib = 740 A
Iz = 1050 A
L = 17m
PVC
QF1
T6D800
QF2
WC2
6x(1x300)+2x(1x150)+1G300
Ib = 540 A
Iz = 682 A
L = 25 m
PVC
QS2
T5D630
IkA=74 kA
QF3
XT4L250 EKIP LSI In250
WC3
3x(1x150)+1x(1x95)+1G95
Ib = 200 A
Iz = 275 A
L = 10m
PVC
L1
In = 200 A
QF4
QF5
QF6
WC4
3x(1x95)+1x(1x50)+1G50
Ib = 200 A
Iz = 207 A
L = 40m
PVC
L2
In = 200 A
L3
In = 170 A
L4
In = 170 A
WC5
3x(1x95)+1x(1x50)+1G50
Ib = 170 A
Iz = 207 A
L = 60m
PVC
WC6
3x(1x95)+1x(1x50)+1G50
Ib = 170 A
Iz = 207 A
L = 30m
PVC
IkA=54.5 kA
Installation with PR223EF
Since the rated current and the short-circuit values of the network under consideration remain unchanged, the use of the new protection
release PR223EF allows selectivity to be obtained without increasing the size of the apparatus to be used.
In particular, a T5L630 equipped with PR223EF can be used as circuit-breaker on the supply side of switchboard B (QF2). As a conse-
quence, the switch-disconnector on the incoming feeder of switchboard B can be reduced in size.
The most evident reduction in size which can be obtained regards the main device of the installation: thanks to the use of PR223EF
release, a moulded-case circuit-breaker can be chosen instead of an air circuit-breaker. In this specific case, a T6L800 circuit-breaker
with a downstream switch-disconnector of the same size can be used.

The following table summarizes the advantages deriving from the use of the new electronic release.
In details, it has been possible:
• to replace a large-sized moulded-case circuit-breaker with a smaller one – T5L 630 PR223EF instead of T6L630 PR221-LS;
• to replace a large-sized air circuit-breaker with a much smaller moulded-case one – T6L 800 PR223EF instead of E3H800 PR122/P-
LSIG;
• to replace a large-sized switch-disconnector with a smaller-sized one – T5D 630 instead of T6D630;
• to replace an air switch-disconnector with a switch-disconnector derived from a much smaller-sized moulded-case circuit-breaker
– T6D 800 instead of E2.2H/MS.

Besides a remarkable reduction in the applicable sizes, with the consequent advantages from a dimensional and economical point of
view, the installation equipped with PR223EF releases is subject to more limited electrodynamical and thermal stresses than those of the
traditional solution. Hereunder the let-through energy and peak curves relevant to the considered circuit-breakers are shown.
From the curves above, it should be noticed that at a short-circuit current value corresponding to 55kA, the specific let-through energy
allowed by T6H630 is equal to 13 MA2
s, whereas that of T5L630 is 3.5 MA2
s. Also the peak values decrease drastically from 54kA of T6H
to about 35kA of T5L630.
Similarly, at 74kA short-circuit current, the specific let-through energy and the peak current limited by T6L800 circuit-breaker reduce very
much the thermal and dynamical stresses if compared with E2.2H circuit-breaker.
In particular, in this case, it is possible to use the current limiting capacities of the moulded-case circuit-breaker to optimize the dimen-
sioning of the busbar system of switchboard A. In fact, with an air circuit-breaker on the supply side, it is necessary to adopt a busbar
system dimensioned for a rated short-time withstand current (Icw) equal to 75kA and consequently with a current carrying capacity much
more higher than the total current required by the installation. On the contrary, by using a T6L800 circuit-breaker on the supply side of
the switchboard, it is possible to adopt a busbar system with Icw equal to 35kA, which results more consistent from a dimensional point
of view with 800A current, which is the current carrying capacity required to this busbar system.
In details, the following values correspond to 35kA rated short-time withstand current of the busbar system:
- peak current Ip = (35x2.1) = 73.5kA, which results to be higher than the peak of 66kA allowed by T6L800 circuit-breaker at 75kA short-
circuit current;
- let-through energy I2
t = 352
x 1 =1225 MA2
s, which results to be higher than the let-through energy equal to 20MA2
s of T6L800 circuit-
breaker with a short-circuit value corresponding to 75kA.
10 kA
1 MA2
s
103
kA
Irms [kA]
10 MA2
s
102
MA2
s
I2
[MA2
s]
E2.2H 800
T5L 630
T6L 800
T6H 630
102
kA
103
MA2
s
10 kA 103
kA
Irms [kA]
Ip[kA]
E2.2H 800
T5L 630
T6L 800
T6H 630
102
kA
10 kA
103
kA
102
kA
Let-through energy curve Peak curve
Traditional solution Solution with EFDP
Busbars of
switchboard A
Icw = 75kA Icw = 35kA
Traditional solution Solution with EFDP
E2.2H800 EKIP TOUCH In800
E2.2H/MS
T6L630 PR221DS
T6D630
T6L800 PR223EF
T6D800
T5L630 PR223EF
T5D630
QF1
QS1
QF2
QS2

The case where selectivity is required between an air
circuit-breaker on the supply side and a moulded-case
circuit-breaker on the load side is now analysed.
In this case, two paths can be followed:
- traditional solution with time/energy selectivity;
- zone selectivity, when the load-side circuit-breaker is
a Tmax equipped with a PR223EF release and the
Emax 2 on the supply side is equipped with an Ekip
Touch or Ekip Hi Touch release.
Traditional solution
In this case, ABB SACE makes a table available in which the selectivity values between air circuit-breakers on the supply side and
moulded-case circuit-breakers on the load side are given.
The need to set the releases appropriately to obtain the selectivity value given in the table is obvious.
The following must be true:
In the overload zone, the load-side circuit-breaker must trip more rapidly than the supply-side circuit-breaker, taking into consideration
the tolerances and the real currents circulating in the circuit-breakers.
- instantaneous protection function I must be set to OFF
I3=OFF
- the I2A
trip threshold of the supply-side circuit-breaker must
be adjusted so as not to create trip overlapping with the trip
threshold of the protection against short-circuit (I3 or I2) of
the load-side circuit-breaker, taking into consideration the
tolerances and the effective currents circulating in the circuit-
breakers
- with regard to the t2 trip time of function S, the settings of the
Emax on the supply side are indicated hereunder, according
to the setting/type of MCCB on the load side:
when the I2A
lowing is valid:
t2A
≥ 100ms both if I2
t =cost as well as if t =cost
when the I2A
threshold of the supply-side circuit-breaker is only higher than the I2B
threshold of the load-side circuit-breaker, by
using curves with the same characteristics, the following is valid:
t2A
- tolerance ≥ t2B
+ tolerance + 50ms
The Is ultimate selectivity limit obtained is the one given in the “Coordination Tables” publication.
Note
The indications about the adjustments of the releases are valid in general and useful for a rapid choice of settings guaranteeing selectivity. For speci-
fic combinations of circuit-breakers and for specific installation conditions, ABB SACE may provide indications which do not respect the rules given
in this document, but however able to ensure selectivity.
B A
Emax 2-MCCB selectivity
0.1kA 1kA 10kA
103s
102s
10s
1s
10-1s
10-2s
104s
Version
Release
Iu [A]Loadside
ACB - MCCB @ 400/415 V
Supply
side
XT1
B
C
N
S
H
TM
E1.2 E2.2 E4.2
B C N L
EL EL EL
800
1000
1250
1600
1600
2000
3200
4000
160
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
630
800
1000
1250
1600
630
800
1000
1250
1600
630
250
800
1000
1250
630
42
42 50
B N S H
800
1000
1250
1600
2000
2500
800
1000
1250
1600
2000
2500
250 800
1000
1250
1600
2000
2500
N S H V
3200
4000
3200
4000
3200
4000
2000
2500
66 66
t2 times set
ACB on the supply side t2A
=200 t2A
=200 t2A
=400 t2A
=700
=50 t2B
=100 t2B
=250 t2A
=500
This relationship must be respected when, through the dialogue or the PR010T unit, electronic settings are used. In the more frequent
case - use of the available settings through dip-switches - the values given in the following tables must be complied with:

The S51/P1 contact is a clean and normally open contact, requiring
an auxiliary power supply at 24V to supply the locking signal to the
supply side relays in the selectivity chain.
The contact is located inside the release and is made available
by means of connector X3. By programming it appropriately, it is
possible to send the locking signal to the SZi input of the supply
side release. Contact programming can be carried out by means of
SDTestBus2, PR010/T and all the programming instruments which
can communicate via ModBus.
S51/P1
PR223EFFPR223EFPR223EF
Ekip Touch
SZi
=max1000m
Cable RS485
S51/P1 S51/P1
Zone selectivity between Emax 2 and Tmax
By means of the programmable contact S51/P1 on the Tmax circuit-breakers, it is possible to extend zone selectivity from the PR223EF
releases to the Ekip Touch or Ekip Hi Touch releases on the supply side.
In practice, the contact makes interfacing between IL protocol of PR223EF and ZS zone selectivity of the releases for Emax 2 and Tmax
possible.
By making this selectivity chain between Emax 2 and Tmax the limit selectivity value shall be the lesser value between:
- the short-time withstand current of the supply-side circuit-breaker (Icw of the Emax)
- the breaking capacity of the circuit-breaker on the load side (Icu of the Tmax in version L → 100kA)

Zone selectivity between Emax 2 and Tmax
0.1kA 1kA 10kA
selectivity time
AC
t2A
B
103s
102s
10s
1s
10-1s
10-2s
104s
As better illustrated in the chapter dedicated to zone selectivity between Emax 2, if zone selectivity on function S is enabled on a Ekip
Touch or Ekip Hi Touch release, two situations can occur:
- the Emax 2 release receives a “lock” signal: if its I2 threshold has been exceeded, it trips within the t2 time set on the release;
- the Emax 2 release does not receive a “lock” signal: if its I2 threshold has been exceeded, it trips within a “selectivity time” time
set on the release.
Overload
- Check that there is no trip overlapping of protection functions L
Short-circuit
- Trip times t2A
and “selectivity time” of the Emax 2 on the supply
side adjusted in the following way:
selectivity time adjusted so as to realise time-current se-
lectivity with the C device on the load side
placed outside the zone selectivity chain
t2A
(time of function S) adjusted so as to guarantee no tripping
of circuit-breaker A that receives the lock
signal, i.e. according to the relationship:
t2A
> t2B
+70ms*

*∆t minumum between the trip times of two
CBs in series, with auxiliary power supply, and
with constant time curves, to guarantee no trip
of the CB on the supply side.
Instantaneous protection function against short-circuit I set to OFF:
I3 = OFF
This being stated, to obtain total selectivity, both in the case of over-
load and short-circuit, making the selections and settings described
below is recommended, where:
A is the Emax 2 with Ekip Touch on the supply side of the PR223EF
B is the Tmax with PR223EF
C is a device outside the zone selectivity chain
A and B are interconnected by means of the S51/P1 contact
PR221DS
A
B C
S51/P1
PR223EF
Ekip Touch

103s
102s
10s
1s
10-1s
10-2s
104s
ACB-ACB Selectivity
The case where selectivity is required between two air circuit-breakers is now analysed. In this case various methods
can be used to obtain selectivity between the circuit-breakers:
time selectivity for combinations of Emax 2 with any type of release
zone selectivity for combinations of Emax 2 with Ekip Touch and Ekip Hi Touch releases
directional time selectivity for combinations of Emax 2 with Ekip Hi Touch releases
directional zone selectivity for combinations of Emax 2 with Ekip Hi Touch releases.
Time selectivity
To obtain the maximum level of selectivity compatible with the chosen strategy, both in the case of overload and short-circuit, the following
selections and the following settings between the various circuit-breakers are recommended:
Minimum difference between the t2 times of two Emax 2 circuit-breakers equipped with Ekip Dip, Ekip Touch and Ekip Hi Touch
t=const t2A > t2B + 100ms* *70ms if in aux supply or in self-supply under steady conditions
I2
t=const t2A > t2B + 100ms t2A < 400ms
I2
t=const t2A > t2B + 200ms t2A ≥ 400ms

Note
The indications about the adjustments of the releases are valid in general and useful for a rapid choice of settings guaranteeing selectivity. For specific
combinations of circuit-breakers and for specific installation conditions, ABB SACE may provide indications which do not respect the rules given in this
document, but however able to ensure selectivity.
With regard to the ultimate selectivity limit
- If instantaneous function I is set to ON (I3=ON), the ultimate selectivity limit will be the value of the I3 instantaneous trip threshold of
the supply-side circuit-breaker less its tolerance:
Is = I3minA
- If instantaneous function I is set to OFF (I3=OFF), the ultimate selectivity limit is equal to the Icw value of the supply-side circuit-breaker:
Is = Icw.
Overload
Short-circuit
- The instantaneous protection function I of the supply-side circuit-
breaker must be set to OFF
I3A
=OFF
- the I2A
trip threshold of the supply-side circuit-breaker must be
adjusted so as not to create trip overlapping with the trip threshold
of the protection against short-circuit (I3 or I2) of the load-side
circuit-breaker, taking into consideration the tolerances and the
real currents circulating in the circuit-breakers
- with regard to the t2 trip times of function S, no overlapping of
the curves and the following relationships must be respected:

Fault current
Connection with lock signal
Connection without lock signal
A
B
C
Ekip Touch
Ekip Touch
Ekip Touch
Ekip Touch
Ekip Touch
Ekip Touch
Ekip Touch
Ekip Touch Ekip Touch
Ekip Touch
Ekip Touch
Ekip Touch
t2A
t2B
t2A
does not
trip
selectivity
timeA
selectivity
timeB
selectivity
timeC
does not
trip
does not
trip
Zone selectivity between Emax 2
By means of zone selectivity, it is possible to obtain selectivity between Emax 2 circuit-breakers, notably reducing the trip times by
obtaining lower curves that can facilitate the search for selectivity towards the medium voltage circuit-breakers.
By reducing the trip times, the thermal stresses on all the components of the installation during the fault are also reduced.
Zone selectivity between Emax 2 circuit-breakers, applicable to protection functions S and G, can be enabled in the case where:
- the fixed time curve is selected for these protections;
- there is a 24V auxiliary power supply source;
- the Emax 2 circuit-breakers are equipped with Ekip Touch and Ekip Hi Touch releases.
The ultimate selectivity limit obtained is equal to the Icw of the supply-side circuit-breaker if the I3 is set to OFF
The operating principle of zone selectivity between Emax 2 is described below.
By zone the part of the installation included between two circuit-breakers in series is intended. The fault zone is the one immediately to
the load side of the circuit-breaker which detects the fault. By means of a simple connection wire, each circuit-breaker which detects a
fault communicates this to the one on the supply side.
The circuit-breaker which does not receive any communication from those on the load side will launch the opening command in the
selectivity time set, adjustable from 40 to 200ms.
The aim of the selectivity time is to realise time selectivity towards pieces of apparatus connected on the load side which are outside
the zone selectivity chain (apparatus not cabled).
On the other hand, the circuit-breakers which receive a lock signal from another release, will trip according to the t2 time set of protection S.
As can be seen, if the settings indicated below have been respected, in the case of a short-circuit no circuit-breaker trips in the t2 time,
but all of them trip within the selectivity time set.
A
B
Lock signal
Fault current
A
B
Lock signal
Fault current
A t2A
B selectivity time
A selectivity time
B closed

Zone selectivity between Emax 2
t2A
time of selectivityA
103s
102s
10s
1s
10-1s
10-2s
104s
Overload
Short-circuit
- Trip times t2 and “selectivity time” adjusted in the following way:
selectivity time adjusted so as to realise time-current selecti-
vity with any device connected directly on the load side placed
outside the zone selectivity chain

t2 (time of function S) adjusted so as to guarantee no trip of the
protection which receives the lock signal, i.e. according to the
relationship:
t2A
> selectivity timeB
+70ms*
*∆t minumum between the trip times of two CBs in series, with auxiliary
power supply, and with constant time curves, to guarantee no trip of the
CB on the supply side.
To obtain total selectivity, both in the case of overload, short-circuit and earth fault, using the “zone selectivity” function, making the
following selections and the following settings between the various circuit-breakers is recommended:
A
B
With regard to the ultimate selectivity limit
- If the instantaneous function I is set to ON (I3=ON), the ultimate selectivity limit will be the value of the I3 instantaneous trip threshold
of the supply-side circuit-breaker less its tolerance, if this function is enabled:
Is = I3minA
- If the instantaneous function I is set to OFF (I3=OFF), the ultimate selectivity limit is equal to the Icw value of the supply-side circuit-
breaker:
Is = Icw.
ACB-ACB Selectivity

Indications about cabling
To carry out the cabling, a shielded twisted pair cable can be used (Vn≥50V; AWG 22; nominal conductor DC resistance@20°C ≤15
Ohm/1000ft; nominal outer shield DC resistance@20°C ≤3 Ohm/1000 ft). The shield must only be connected to earth on the release of
the supply-side circuit-breaker.
The maximum cabling length for zone selectivity between two units is 300 metres. This limit can be increased with special devices.
The maximum number of circuit-breakers which can be connected to the outputs (Z out) of a release is 20.
The lock signal of the release is a +24V signal.
Repetition of the signal
As shown in the table, in the case where one release receives the lock signal on the load side, even if it has not entered the threshold of
function S, it will repeat the lock signal on the supply side.
This to avoid any setting errors, i.e. a release on the load side not having entered the threshold, but a release on the supply side having
entered the threshold, leading to lack of selectivity:
Zone Selectivity I > I2 ZSI signal ZSO signal T trip time
Excluded NO 0 0 no trip
Excluded NO 1 0 no trip
Excluded YES 0 0 t2 programmed
Excluded YES 1 0 t2 programmed
Inserted NO 0 0 no trip
Inserted NO 1 1 no trip
Inserted YES 0 1 selectivity time
Inserted YES 1 1 t2 programmed
Zone Selectivity with Ekip Link
With Ekip Link proprietary communication protocol, the Emax 2 circuit breaker can do many things:
- complex logic selectivity, avoiding complex wiring;
- provide redundancy, coupling the Ekip Link bus with the standard cabling (hard-wired selectivity);
- configurable diagnostic to test the hard-wired selectivity, e.g. the integrity of the shielded twisted
pair cable.
These are the main steps to put the system into operation:
a) the Ekip Link Modules enable the communication among Sace Emax 2 circuit breakers (called Actors
from now on), provide one module for every circuit-breaker. Up to 12 Actors can be connected;
b) set-up the network, e.g. set the IP address for every Actor;
c) in case more than two Actors are involved in the selectivity chain, use an Ethernet switch to manage
the Ekip Link signals;
d) with Ekip Connect (the ABB Sace software for the configuration of the electronic trip units), configure
the selectivity options: which signals will be received and which will be reflected to the next Actor;
e) set the protection functions properly. S, S2, G, Gext, D protections can interact in many ways, set
them to activate the selectivity.
Find more information about Ekip Link on the Emax 2 technical catalogue, or learn how to set-up Ekip
Link for logic selectivity on both, the Emax 2 installation manual and the “Operating instructions for
the design engineer”.

Directional time selectivity
By means of the directional protection D (ANSI 67) present on the Emax 2 circuit-breakers equipped with Ekip Hi Touch releases, it is
possible to realise time selectivity of directional type.
This type of selectivity has all the advantages and limits of time selectivity realised by means of function S, but is also able to trip within
different times according to the direction of the fault.
Using this type of selectivity is particularly recommended in those cases where there is more than one power supply source.
In fact, in the case of a fault near a source, service continuity of the remaining power supply can be guaranteed by means of
directional protection.
Directional protection
Directional protection is based on the possibility of correlating the circuit-breaker behaviour with the direction of the fault current which
passes through it in relation to the reference direction that can be set on the release.
According to the direction of the current, it is possible to set two different trip times on the Ekip Hi Touch release:
a time (t7Fw) in a direction concordant (Fw) with the reference direction set;
a time (t7Bw) in a direction discordant (Bw) with the reference direction set.
These times are enabled when the only current threshold (I7) set on the Ekip Hi Touch release is exceeded.
If the fault current is discordant (Bw) with the reference direction set, the protection will trip once the I7 threshold in the t7Bw time set is
reached (unless functions S and I are not set to intervene before D).
If the fault current is concordant (Fw) with reference direction set, the protection will trip once the I7 threshold in the t7Fw time set is
reached (unless functions S and I are not set to intervene before D).
Furthermore, if function I is enabled and the short-circuit current exceeds the I3 value set, the circuit-breaker will open instantaneously
regardless of the direction of the current.
The default reference direction is from the top of the circuit-breaker (zone where the release is) to the bottom (top to bottom).
To realise directional time selectivity, it is necessary to assume the significant fault points and, having assessed the short-circuit currents
concerned, establish which circuit-breakers will have to trip.
To be sure that everything functions as foreseen in the case of a fault, i.e. the circuit-breakers always trip with directional protection, the
following settings and selections are recommended:
- Select the circuit-breakers with a short-time withstand current value higher than the maximum prospective short-circuit current
which can occur at the point where they are installed:
Icw ≥ Ik MAX
- Set the trip thresholds of directional protections D to a lower value than the minimum prospective short-circuit current which can
occur at the point where that release is installed:
I7 < Ik min
- Set the trip thresholds of protections S and I in such a way so as not to create trip overlapping with function D.
Also remember that, in the case of constant time curves, to guarantee tripping of an air circuit-breaker equipped with Ekip Dip, Ekip
Touch or Ekip Hi Touch and no trip of another air circuit-breaker equipped with these releases, a difference between the trip times set
must be kept, equal to:
∆t = 100ms (which can be reduced to 70ms if there is an auxiliary power supply or if it is considered that the fault occurs when the
releases under self-supply are in a steady condition).
The figure at the side shows the actual configuration which two
circuit-breakers have in an installation.
The default reference direction set on the circuit-breaker is indicated
by the red arrow.
If the circuit-breaker power supply direction is from top to bottom
(power supply from G2), the reference direction remains the ABB
default one.
If the circuit-breaker power supply direction is from bottom to top
(power supply from G1), by working on its software, the new Ekip
Hi Touch electronic release allows the default setting to be reversed
(bottom to top).
Working in this way, all the values measured with the PR123 release
will be assessed as they actually flow in the installation. Furthermore,
on the single-line diagram which represents the installation, the refe-
rence direction to carry out a selectivity study and consider the Bw
or Fw trip directions correctly always remains from top to bottom.
In the single-line diagram at the side, the reference directions are
indicated in red. If the circuit-breakers are considered to be supplied
as described in the previous figure, there is the following: for QF2 it
is the default direction, whereas for QF1 it is the direction reversed
by means of the software.
A
G2G1
Other passive
loads M
Contribution of the
motor to the
short-circuit: 5kA
B
C
D E QF4QF3
with Ekip LSI
Reference
direction
Reference
direction
QF1
with Ekip Hi Touch
QF2
with Ekip Hi Touch
Contribution to the
short-circuit by each
generator: 10 kA
Reference
direction
inverted
through
software
Reference
direction
set by
ABB
G2G1
Release
Direction
set by
ABB
Release
ACB-ACB Selectivity

Example of application
With reference to the installation in the figure, the different operating conditions of the circuit-breakers in relation to the different fault
points are analysed.
* Minimum ∆t between the trip times of two CBs in series, without an auxiliary power
supply and not in steady conditions, to guarantee no trip of the CB on the supply side
The ultimate selectivity limit which is obtained is equal to the Icw of the circuit-breakers if I3=OFF.
Protection functions
CB
QF1
QF2
QF3
QF4
S
OFF
OFF
OFF
t2
200ms
I2
3kA
I7
3kA
3kA
-
3kA
D
t7FW
300ms
300ms
-
200ms
t7BW
200ms
200ms
-
300ms
I
I3
OFF
OFF
OFF
OFF
Fault on the load side of QF4
Only QF4 must trip.
QF1 detects a current 10 kA concordant with its reference
direction, and will therefore trip in the t7FW1
time
direction, will therefore trip in the t7FW2
time
QF3 does not detect any fault current
direction, will therefore trip in the t7FW4
time
If: t7FW1
> t7FW4
+100ms*
t7FW2
> t7FW4
+100ms*
therefore QF4 only will trip
Summarising, the settings possible which respect the limits imposed are:
A
G2G1
M
Contribution of the
motor to the
short-circuit: 5kA
B
C
D E
QF4
QF3
with Ekip LSI
Reference
direction
Reference
direction
QF1
with Ekip Hi Touch
QF2
with Ekip Hi Touch
Contribution to the
generator: 10 kA
Other passive
loads
Contribution of the
motor to the
short-circuit: 5kA
QF3
with Ekip LSI
Reference
direction
Reference
direction
QF1
with Ekip Hi Touch
QF2
with Ekip Hi Touch
Contribution to the
generator: 10 kA
A
G2G1
M
B
C
D E
QF4
Other passive
loads
Contribution of the
motor to the
short-circuit: 5kA
QF3
with Ekip LSI
Reference
direction
Reference
direction
QF1
with Ekip Hi Touch
QF2
with Ekip Hi Touch
Contribution to the
generator: 10 kA
QF4
Other passive
loads
A
G2G1
M
B
C
D E
Contribution of the
motor to the
short-circuit: 5kA
QF3
with Ekip LSI
Reference
direction
Reference
direction
QF1
with Ekip Hi Touch
QF2
with Ekip Hi Touch
Contribution to the
generator: 10 kA
QF4
Other passive
loads
A
G2G1
M
B
C
D E
Fault on the supply side of QF1
Only QF1 must trip.
QF1 detects a current of 15kA discordant with its reference
direction, and will therefore trip in the t7BW1
time
QF2 detects a current of 10 kA concordant with its reference
time
time
If: t7FW2
> t7BW1
+100ms*
t7BW4
> t7BW1
+100ms*
Fault on the supply side of QF2
Only QF2 must trip.
time
QF2 detects a current 15kA discordant with its reference direc-
tion, and will therefore trip in the t7BW2
time
time
If: t7FW1
> t7BW2
+100ms*
t7BW4
> t7BW2
+100ms*
Fault on the load side of QF3
Only QF3 must trip.
time
time
QF3 detects a fault current of 25kA
QF4 detects a current 5kA discordant with its reference direction,
and will therefore trip in the t7BW4
time
If: t7FW1
> t23
+100ms*
t7FW2
> t23
+100ms*
t7BW4
> t23
+100ms*

Directional zone selectivity
This function allows selectivity to be obtained even in mesh networks and ring networks.
In particular, in the presence of a bus tie, thanks to directional zone selectivity it is possible to keep a half-busbar supplied with voltage
even in the case of a fault on the other half-busbar.
To apply zone selectivity to function D (directional zone selectivity), a series of conditions must exist:
- zone selectivity S and G must be disabled [OFF]
- there is a 24Vdc auxiliary power supply source
- the Emax 2 circuit-breakers are equipped with the Ekip Hi Touch releases
- Ekip Touch releases equipped with Ekip Link module (optional, for logical selectivity only).
Each release has 4 ports available:
- two inputs (one in a concordant and one in a discordant direction), through which the release receives the lock signal coming from
other releases
- two outputs (one in a concordant and one in a discordant direction), through which the release sends the lock signal to other releases.
The behaviour of the release is described below:
The circuit-breakers which do not receive a lock signal (coordinated with the direction of the current) will launch their own opening com-
mand in a time equal to the ”selectivity time” which can be adjusted from 130 to 500ms.
The circuit-breakers which receive the lock signal (coordinated with the direction of the current) will time according to the t7BW or t7FW
times depending on the direction of the current.
It is important to remember that if function I is enabled, and the short-circuit current exceeds the value set (I3), the circuit-breaker will
open instantaneously and regardless of the directions and signals received.
In the same way, if function S is enabled and the short-circuit current exceeds the value set (I2), the circuit-breaker will open in the t2
time, if this is shorter than the other times, regardless of the directions and signals received.
By using directional zone selectivity, it is possible to obtain selectivity even in meshed networks up to an ultimate selectivity limit equal
to the Icw of the circuit-breakers furthest on the supply side (if the I3=OFF).
In the same way as for directional protection, to be sure that everything functions as foreseen in the case of a fault, i.e. the circuit-breakers
always trip with directional protection, the following settings and selections are recommended:
- Select the circuit-breakers with a short-time withstand current value higher than the maximum prospective short-circuit current
which can occur at the point where they are installed:
Icw ≥ IkMAX
- Set the trip thresholds of directional protections D to a lower value than the minimum prospective short-circuit current which can
occur at the point where that release is installed:
I7 < Ikmin
- Set the trip thresholds of the protections S and I in such a way so as not to create trip overlapping with the function D.
By means of these settings, it is certain that, for any foreseeable fault in the installation, the circuit-breakers will trip according to the
settings of function D.
The trip times must be adjusted remembering that:
selectivity time is the trip time of the “unlocked” circuit-breakers which must open;
t7FW/BW is the trip time of the “locked” circuit-breakers which must not open.
Starting from these considerations:
selectivity time must be adjusted so as to realise time-current selectivity with any device connected directly on the load side
placed outside the zone selectivity chain
t7FW/BW adjusted so as to guarantee no trip of the protection which receives the locked signal i.e. according to the
relationship:
t7 > selectivity time +70ms*
*∆t minimum between the trip times of two CBs in series, in auxiliary power supply, to guarantee that the CB on the supply side does not trip.
ACB-ACB Selectivity

With reference to the installation indicated in the figure, once the maximum and minimum short-circuit currents in the different points of
the installation are known, it is necessary to:
- hypothesize the various significant fault points;
- for the first fault: establish which circuit-breakers must isolate the fault;
establish which circuit-breakers must be locked and by what;
draw the appropriate cabling;
- repeat the operation for the subsequent faults in order to determine all the necessary cabling.
Finally, it is necessary to check that the cabling carried out does not create any conflicts.
Application example
The main faults which can be hypothesised are as follows:
fault in B1
fault in B2
fault on the load side of QF4
fault on the load side of QF5
fault on the supply side of QF1
fault on the supply side of QF2
An application example of this selectivity technique is now illustrated. This example also shows which procedure must be used to de-
termine the cabling required between the various releases.
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
-TM1 -TM2
QF1+ QF2+
QF3+ QF5+QF4+
M
-B2-B1
L
Reference direction
Ekip Hi Touch
Ekip Hi Touch
Ekip Hi Touch
Ekip Hi Touch
Ekip Hi Touch
Note
The QF4 circuit-breaker could be provided with Ekip Touch release since, with a passive load, the short-circuit current may have a single direction and con-
sequently directional protection results to be unnecessary.
The use of Ekip Touch release, with zone selectivity implemented on protection S, guarantees an input and an output, which allow to realise selectivity in the
case of a fault on the load side of QF4.

Fault in B1:
Only the QF1 and QF3 circuit-breakers must interrupt the fault: in particular the QF3 circuit-breaker is passed through by a current
coming from busbar B2 (therefore in a direction concordant with the one set); the OUT Fw bus sends a lock signal to the IN Fw bus of
the QF2 circuit-breaker (passed through by a current coming from transformer TM2 and therefore in a direction concordant with the one
set), and to the IN Bw bus of the QF5 circuit-breaker (passed through by a current coming from the motor and therefore in a direction
discordant with the one set).
Fault in B2:
The QF2 and QF3 and QF5 circuit-breakers must interrupt the fault: in particular the QF3 circuit-breaker is passed through by a current
coming from busbar B1 (therefore in a direction discordant with the one set); the OUT Bw bus sends a lock signal to the IN Fw bus of the
QF1 circuit-breaker (passed through by a current coming from transformer TM1 and therefore in a direction concordant with the one set).
Cabling
OUT
QF1 QF2 QF3 QF4 QF5
QF1
QF2
QF3
QF4
QF5
IN
FW
BW
FW
BW
FW
BW
FW
BW
FW
BW
FW BW FW BW FW BW FW BW FW BW
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
-TM1 -TM2
QF1+
Ekip Hi
Touch
QF2+
QF3+
Ekip Hi
Touch
QF5+QF4+
Ekip Hi
Touch
M
-B2-B1
L
Direction (OUT-IN)
Fw Fw
Bw Bw
Fw Bw
Bw Fw
Arrow
Reference direction
Ekip Hi
Touch
Ekip Hi
Touch
Direction (OUT-IN)
Fw Fw
Bw Bw
Fw Bw
Bw Fw
Arrow
Reference direction
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
-TM1 -TM2
QF1+ QF2+
QF3+ QF5+QF4+
M
-B2-B1
L
Ekip Hi
Touch
Ekip Hi
Touch
Ekip Hi
Touch
Ekip Hi
Touch
Ekip Hi
Touch
ACB-ACB Selectivity

Fault on the load side of QF4:
Only the QF4 circuit-breaker must interrupt the fault. The QF4 circuit-breaker is passed through by a current coming from busbar B1
(therefore in a direction concordant with the one set); the OUT Fw bus sends a lock signal to the IN Fw bus of the QF1 circuit-breaker
(passed through by a current coming from transformer TM1 and therefore in a direction concordant with the one set), and to the IN Fw
bus of the QF3 circuit-breaker (passed through by a current coming from busbar B2 and therefore in a direction concordant with the one
set).These two cabling operations must be carried out.
The QF3 circuit-breaker will then lock the circuit-breakers which insist on busbar B2 by means of the cabling already carried out.
Fault on the load side of QF5:
In this case only the QF5 circuit-breaker must interrupt the fault. The QF5 circuit-breaker is passed through by a current coming from the
busbars B1 and B2, in a concordant direction in relation to the direction set, therefore the OUT Fw bus of QF5 locks both the IN Fw bus
of QF2 (passed through by a current coming from TM2 and therefore in a direction concordant to the one set) and the IN Bw bus of QF3
(passed through by a current coming from TM1 and therefore in a direction discordant with the one set). These cabling operations must
be carried out. In the same way as before, the QF3 circuit-breaker locks QF1 with the cabling already present.
Cabling
OUT
QF1 QF2 QF3 QF4 QF5
QF1
QF2
QF3
QF4
QF5
IN
FW
BW
FW
BW
FW
BW
FW
BW
FW
BW
Direction (OUT-IN)
Fw Fw
Bw Bw
Fw Bw
Bw Fw
Arrow
Reference direction
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
-TM1 -TM2
QF1+
Ekip Hi
Touch
QF2+
QF3+ QF5+QF4+
M
-B2-B1
L
Ekip Hi
Touch
Ekip Hi
Touch
Ekip Hi
Touch
Ekip Hi
Touch
Direction (OUT-IN)
Fw Fw
Bw Bw
Fw Bw
Bw Fw
Arrow
Reference direction
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
-TM1 -TM2
QF1+
QF2+
QF3+ QF5+QF4+
M
-B2-B1
L
Ekip Hi
Touch
Ekip Hi
Touch
Ekip Hi
Touch
Ekip Hi
Touch
Ekip Hi
Touch

Fault on the supply side of QF1:
Only the QF1 circuit-breaker must interrupt the fault. The QF1 circuit-breaker is passed through by a current coming from busbar B1
(therefore in a direction discordant with the one set); the OUT Bw bus sends a lock signal to the IN Fw bus of the QF3 circuit-breaker
(passed through by a current coming from transformer TM2 and therefore in a direction concordant with the one set). This cabling must
be carried out.The QF3 circuit-breaker will then lock the circuit-breakers which insist on busbar B2 by means of the cabling operations
already carried out.
Fault on the supply side of QF2:
In this case only the QF2 circuit-breaker must interrupt the fault. The QF2 circuit-breaker is passed through by a current coming from
busbar B2, in a direction discordant with the direction set, therefore the OUT Bw bus of QF2 locks both the IN Bw bus of QF5 (passed
through by a current coming from the motor and therefore in a direction discordant to the one set) and the IN Bw bus of QF3 (passed
through by a current coming from TM1 and therefore in a direction discordant with the one set). These cabling operations must be carried
out. In the same way as before, the QF3 circuit-breaker locks QF1 with the cabling already present.
Cabling
OUT
QF1 QF2 QF3 QF4 QF5
QF1
QF2
QF3
QF4
IN
FW
BW
FW
BW
FW
BW
FW
BW
FW
BW
QF5
Direction (OUT-IN)
Fw Fw
Bw Bw
Fw Bw
Bw Fw
Arrow
Reference direction
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
-TM1 -TM2
QF1+
Ekip Hi
Touch
QF2+
QF3+ QF5+QF4+
M
-B2-B1
L
Ekip Hi
Touch
Ekip Hi
Touch
Ekip Hi
Touch
Ekip Hi
Touch
Direction (OUT-IN)
Fw Fw
Bw Bw
Fw Bw
Bw Fw
Arrow
Reference direction
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
IN
Fw Bw
Fw Bw
OUT
-TM1 -TM2
QF1+ QF2+
QF3+ QF5+QF4+
Ekip Hi
Touch
M
-B2-B1
L
Ekip Hi
Touch
Ekip Hi
Touch
Ekip Hi
Touch
Ekip Hi
Touch
ACB-ACB Selectivity

Having established the cabling system as shown in the table, an example of settings for the installation in question is given:
Apart from realising directional zone selectivity with the settings indicated, selectivity between the QF4 and QF5 circuit-breakers towards
the supply-side circuit-breakers and between QF1 and QF2 can also be achieved, in the case of loss of the auxiliary power supply.
Indications about cabling
A shielded twisted pair cable (not supplied - ask ABB for information) can be used to carry out the cabling.
The shield of the cable must only be connected to earth in correspondence with one of the two releases. When it is possible to identify
the more distant circuit-breaker (on the supply side) between the two, it is advisable to connect the shield to earth in correspondence
with the release which equipping this circuit-breaker.
The maximum length of the cabling between two units for zone selectivity is 300 metres. This limit can be increased using special devices.
The maximum number of circuit-breakers which can be connected to the outputs (Z out) of a release is 20.
The lock signal of the release is a +24V signal.
Protection function
CB
QF1
QF2
QF3
QF4
QF5
S
OFF
OFF
OFF
OFF
OFF
t2I2 I7
<Ikmin
<Ikmin
<Ikmin
<Ikmin
<Ikmin
t7FW
350ms
350ms
300ms
250ms
250ms
t7BW
250ms
250ms
300ms
350ms
350ms
I
I3
OFF
OFF
OFF
OFF
OFF
Selectivity
time
150ms
150ms
150ms
150ms
150ms
D

AppendixA
Appendix A
MV/LV Selectivity
General
Before facing the problem of the selectivity between the
medium and low voltage circuit-breaker, it is first neces-
sary to clarify the functions of these circuit-breakers:
• the MV protection on the supply side of the
transformer must:
- protect the transformer against short-circuit
- protect the transformer against faults on the
supply side of the main LV circuit-breaker
(if a dedicated protection is not provided)
- not intervene when the transformer is sup-
plied with voltage (inrush current – inrush)
- be set so as to satisfy the limits imposed
by the distributor utility
- be set so as to be selective with the pro-
tections on the supply side (if requested)
• the LV protection on the load side of the tran-
sformer must:
- protect the transformer against short-circuit
and overload (*)
- be set so as to be selective with the pro-
tections on the load side.
To carry out the selectivity study between two medium
and low voltage circuit-breakers, the data indicated be-
low must first be put into a logarithm diagram (referring
to a single reference voltage):
1. transformer:
• connection curve (inrush);
• rated current;
• short-circuit current at the LV busbars;
• short-circuit withstand capacity of the
transformer;
2. utility:
• maximum current and time limits which
can be set for the protections required;
At this point, the trip curves of the main low voltage
circuit-breaker must be traced so that:
• protection of the transformer against overload
is verified (threshold I1 of protection function L
close to the rated current of the transformer);
• it is selective with the other low voltage circuit-
breakers on the load side.
Once the LV protection is defined, the curve of the me-
dium voltage circuit-breaker voltage is traced so that:
• it protects the transformer against overloads (this
protection is usually ensured by the low voltage
circuit-breaker);
• it stays above the inrush current curves of the
transformer;
• it stays below the representative point of the
thermal withstand (this protection can be carried
out by the low voltage circuit-breaker, but any
short-circuit between the low voltage circuit-
breaker and the terminals of the transformer
remains unprotected);
• it stays below the limits set by the distributor
utility.
Example
The selectivity study for the network represented in the figure is to be carried out:
Data:
• Distributor utility:
- rated voltage Un
= 15 kV
- three-phase short-circuit current Ik3
= 12.5 kA
- single-phase earth fault current Ik1E
= 50 A
- overcurrent protection 51:
• first threshold: I> ≤ 250 A, t ≤ 0.5 s
• second threshold: I>> ≤ 900 A, t ≤ 0.12 s
• 15/0.4 kV Transformer:
- rated power Sn = 1600 kVA
- short-circuit voltage uk
= 8 %
- rated primary current It1
= 61.6 A
- rated secondary current It2
= 2309.4 A
- inrush current Ii1
= 9⋅It1
= 554.4 A
- inrush time constant tthe
= 0.4 s
- inrush current trend
Iit . e
-t
ti=
2
- short-circuit current Ik3LV2
= 28.9 kA(1 )
- short-circuit current at the transformer busbars
referred to the primary Ik3LV1
= 770 A(1)
- thermal withstand: 770 A for 2 s
• Low voltage circuit-breakers (2)
:
- QF2 E2.2H 2500 Ekip Dip 2500
- QF3 T4H 320 PR222DS/P-LSI In 320A
- QF4 XT2S160 TMD 125
(1) assuming the medium voltage network impedance to be nil
(2) assuming for all protections the respect of the limits imposed by loads
and cables
QF4
XT2S160 TMD 125
QF3
T4H 320 PR222DS/P-LSI In320
QF2
E2.2H 2500 Ekip Dip 2500
Vn1 = 15000 V
Vn2 = 400V
Sn = 1600 kVA
Vk = 8%
QF1
U Vref = 15000 V
(*) The use of a thermometric equipment allows to improve the protection of the transformer against overload.

As described previously, the data regarding the transformer at the
15 kV reference voltage are traced first of all:
Now the data regarding the limits set by the distributor utility are
put in:
Apart from protecting the transformer, the curve of the main low
voltage circuit-breaker must also guarantee selectivity with the
low voltage circuit-breakers. The curves of the low voltage circuit-
breakers can therefore be traced so as to define a minimum limit
for the curve of the main circuit-breaker:
To ensure selectivity between QF3 and QF4, function L and S of T4 must be set as follows:
QF3 T4H 320 PR222DS/P-LSI R320
L: Setting: 0.9x320 = 288 A Curve: 3s
S: t=const Setting: 5.8x320 = 1856 A Curve: 0.1s
I: OFF
103s
102s
10s
1s
10-1s
10-2s
104s
Time-Current Curve
0.1kA 1kA 10kA
Inrush
Thermal
withstand
Ik LV busbars
103s
102s
10s
1s
10-1s
10-2s
104s
Time-Current Curve
0.1kA 1kA 10kA
Distributor utility limits
Time-Current Curve
0.1kA 1kA 10kA
QF3
QF4
103s
102s
10s
1s
10-1s
10-2s
104s
AppendixA

• function L:
- threshold I1 to be adjusted to a value as close as
possible to the rated current of the transformer for
its protection against overload. Since the rated cur-
rent of the transformer is 2309.4 A and taking into
account the uncertainty of the circuit-breaker trip
for currents between 1.05 and 1.2 (in compliance
with IEC60947), the current I1 set can be 2309.4/
(1.2x2500)@0.77xIn (1925)(1 )
- time t1 so as to be sufficiently above the curve of
QF3
• function S:
- threshold I2 to be adjusted to a value higher than
1856 A +10% i.e. 2042.2 A
- time t2 , setting I2over the self-protection value of
the QF3circuit-breaker, it is possible to adjust it to
0.1s
• function I:
- threshold I3 to be adjusted to a value higher than the
short-circuit current there is in correspondence with
QF3. In the case under examination, this current is
the current at the transformer busbars (it is presu-
med that QF2 and QF3 are in the same switchgear
and that there is a negligible impedance).
At this point it is possible to trace the trip curves of the main QF2 LV circuit-breaker bearing in mind the following:
The setting of QF2 are summarised below:
E2.2H 2500 Ekip Dip 2500
L: Setting: 0.77x2500 = 1925 A Curve: 3s
S: t=const Setting: 1.7x2500 = 4250 A Curve: 0.10s
I: Setting: 14x2500 = 35000 A
(1) less restrictive settings can be used when the overloading capacity of the machine is known.
The setting of QF1 are summarised below:
First threshold I> 200 A, 0.35 s
Second threshold I>> 820 A, inst.
• first threshold:
- current higher (30÷35%higher than the current on
the load-side, according to the Publication CEI 0-16
of the Italian Electrotechnical Committee) than the
I2 of the main 125 A low voltage circuit-breaker (I2
+ 10% tolerance, given at 15000 V);
- delay time so as to be selective but lower than the
short-circuit withstand of the transformer and less
than the 0.5 s limit imposed by the distributor utility;
• second threshold:
- current higher than the fault current on the LV side
(increased by 1.2÷1.6 if possible) and less than the
900 A limit imposed by the distributor utility;
- instantaneous trip time.
Now the settings for the medium voltage release are defined, taking into account the following:
Time-Current Curve
0.1kA 1kA 10kA
QF3
QF2
103s
102s
10s
1s
10-1s
10-2s
104s
0.1kA 1kA 10kA
QF3
QF2
QF1
103s
102s
10s
1s
10-1s
10-2s
104s
Time-Current Curve
AppendixA

Appendix B
General considerations about residual
current selectivity
With its many functions and types, the residual current
circuit-breaker can be defined as follows:
a device sensitive to the earth currents, able to open
an electric circuit within a certain time when the earth
current exceeds the preset value. It is used to protect
people and things against: direct contacts (a device with
high sensitivity, it is an additional protection) - indirect
contacts or loss of insulation.
The professional rule for the electrical installation always
imposes, except for special plants, the presence of an
earthing system, both in civil and industrial buildings.
Furthermore, the IEC 60364 Standard makes the use of
a residual current circuit-breaker compulsory in many
cases for protection of people, giving prescriptions
referring to the trip time and currents in relation to the
installation voltage, to the distribution system present,
and to the places of installation.
Good protection of the installation should provide:
- a main residual current type of circuit-breaker so as
to have protection against faults which could occur
between the main circuit-breaker and the distribution;
- protection of each individual shunt with a residual
current device.
In this way, there is the need to study selections of the
devices carefully to guarantee selectivity, and prevent
an earth fault in any point of the distribution circuit from
putting the whole installation out of service.
In general, two residual current devices are selective for
each current value if their trip zones do not overlap. This
condition is obtained by respecting the following points:
- The residual current trip threshold of the device on
the supply side must be higher than or at maximum
equal to double the residual current trip threshold of
the device on the load side:
I∆nSupply side
≥2xI∆nLoad side
.
This relationship is necessary for taking into account
the concept of rated no trip residual current, which
is the maximum current value for which the residual
current circuit-breaker definitely does not trip.
The Standards indicate a current value of I∆n
/2 and
within this value the device does not have definite
behaviour, i.e. it may trip just as it may not trip.
- The minimum no trip time of the circuit-breaker on the
supply side, for each current value, must be higher
than the maximum trip time of the circuit-breaker on
the load side:
Tminsupply
>Ttotload
For residual current circuit-breakers complying with the
IEC60947-2 Standard (CEI EN 60947-2), the prescriptions
regarding the trip curves for residual current without
delay or for the delayed type are given in Annex B of
the Standard.
The differentiation of the trip time can be made more
easily by using delayed type residual current (∆t = time
limit of no trip in ms or if ∆t=60ms) with definite time
or with inverse time, where tripping can be delayed ac-
cording to a selectable time.
These pieces of apparatus are generally installed on the
supply side of other general type residual current devices
and it is advisable to have a relationship of 3 between
the trip thresholds.
Function G
Protection against earth faults can be realised, using the
function G present on the electronic releases installed on
board the moulded-case or air circuit-breakers.
The trip characteristics can be adjusted for the current
(from 0.2 to 1 x In) and for the time, with an inverse or
definite time trend, depending on the different versions.
Realising protection against indirect contacts with this
type of function requires a careful analysis of the distri-
bution system and of the value of the earth fault current.
For Emax 2 circuit-breakers it is possible to realise zone
selectivity for function “G” according to the same philo-
sophy described for function “S”.
This makes it possible to reduce the trip times between
two residual current protections in series, increasing the
safety margin for any fault on the load side of the supply-
side circuit-breaker, since its trip time is not as high as it
should have been to obtain selectivity towards the load
side with the classic method for time selectivity.
AppendixB

Example
An example is given of a network where residual current selectivity on 3 levels is to be realised.
Considering the residual current releases available
RC Inst (Tmax XT1-XT3)
Adjustable trip thresholds I∆n [A] 0.03 – 0.1 – 0.3 – 0.5 – 1 - 3
Trip times [s] instantaneous
RC222 (Tmax T4-T5)
Adjustable trip thresholds I∆n [A] 0.03 – 0.05 – 0.1 – 0.3 – 0.5 – 1 – 3 – 5 - 10
Trip times [s] instantaneous - 0.1 – 0.2 – 0.3 – 0.5 – 1 – 2 - 3
RCQ
Adjustable trip thresholds I∆n [A] 0.03 – 0.05 – 0.1 – 0.3 – 0.5 – 1 – 3 – 5 – 10 - 30
Trip times [s] instantaneous - 0.1 – 0.2 – 0.3 – 0.5 - 0.7 - 1 – 2 – 3 - 5
To obtain selectivity the following device can be used:
RCD 1 type RC Inst installed, for example, on a Tmax XT1
RCD 2 type RC222 installed, for example, on a Tmax T5
RCD 3 type RCQ installed, for example, on an Emax E2.2
characterised by the curves shown in the enclosed time-current diagram.
It can be seen how overlapping of the curves of the 3 devices used is avoided, thereby obtaining selectivity for earth fault.
RCD3 Delayed type t=Is [300mA]
RCD2 Delayed type 300ms [100mA]
Delayed type t=60ms [100mA]
RCD1 Not delayed type [30mA]
Time-Current Curve
1 A10-1 A10-2 A10-3 A
RCD 3RCD 2RCD 1
102s
10s
1s
10-1s
10-2s
10-3s
AppendixB

Example of LV/LV selectivity study
Appendix C
The selectivity study for the installation shown in the figure supplied
by a transformer with a 400V secondary winding is to be carried out:
Four levels are present:
• QF1 E1.2B 1250 Ekip Dip In1250
(Ib
= Intrafo
= 577 A, Iz
= 700 A)
• QF2 T4N 320 PR222DS/P-LSI In 320A (Ib
= 285 A, Iz
= 300 A)
• QF3 XT2N160 (Ib
= 120 A, Iz
= 170 A)
• QF4 S200L C16 (Ib
= 14 A, Iz
= 25 A)
In the study below, it is assumed that the circuit-breakers are passed through by the same fault current (the real currents passing through
the circuit-breakers are ignored) and it is assumed that the circuit-breakers selected are able to protect the cables, the switch-disconnectors
and whatever else.
First of all, the curves of the QF4 circuit-breaker are traced:
QF2
T4N 320
PR222DS/P-LSI
In320
QF1
E1.2B 1250 Ekip Dip In1250
L
Ik = 20kA
Ik = 10.5kA
QF3
XT2N160
TMD In160
Ik = 1.2kA
QF4
S 200L C 16
Time-Current Curve
10 kA1 kA0.1 kA
S 200L C 16 1.2 kA
102s
10s
1s
10-1s
10-2s
103s
104s
AppendixC

Noting that the maximum short-circuit current at the point where QF4 is installed is 1.2 kA, to obtain total selectivity it is sufficient for the
magnetic threshold of the QF3 supply-side circuit-breaker to be higher than this value, taking into account the tolerances:
In any case, a total energy selectivity value, i.e. equal to the breaking
capacity of S200L (6 kA) is found in the coordination tables. The
settings of QF2 will be:
QF2, XT2N160 TMD160
L: Settings: 136 [A]
I: Settings: 1600 [A]
Now the curve of the QF2 T4N 320 circuit-breaker is drawn:
The settings of QF2, in accordance with what has been said in the
previous chapters, will be:
QF2, E1.2B 1250 Ekip Dip In1250
L: Settings: 0.9 Curve: 12s
S: t=const Settings: 8.8 Curve: 0.1s
I: OFF
In this way, in accordance with the coordination tables, the selec-
tivity value will be 25 kA which, in this specific case, means total.
The settings of QF1, in accordance with what has been said in the
previous chapters, will be:
QF1, E1.2B 1250 Ekip Dip In1250
L: Settings: 0.47 Curve: 48s
S: t=const Settings: 3.5 Curve: 0.2s
I: OFF
With these settings, total selectivity, i.e. up to the breaking capacity
of T4N equal to 36 kA, is obtained from the coordination tables.
Finally, the curve of the QF1 E1B 1250 circuit-breaker is drawn:
Time-Current Curve
10 kA1 kA0.1 kA
S200L C16
T2N 160
1.2 kA
102s
10s
1s
10-1s
10-2s
103s
104s
10 kA1 kA0.1 kA
S200L C16
T2N 160
T4N 320
102s
10s
1s
10-1s
10-2s
103s
104s
Time-Current Curve
10 kA1 kA0.1 kA
S200L C16
T2N 160
E1 B1250
T4N320
102s
10s
1s
10-1s
10-2s
103s
104s
Time-Current Curve
AppendixC

When the real currents circulating in the circuit-breakers are to be taken into account, it must be remembered that an overload current of
a load-side circuit-breaker is detected on the supply side amplified by the currents of the other shunts. For this purpose, the installation
just seen above will be considered, assuming that there are two other 100 A loads:
The most critical condition is analysed, taking into consideration the trip times with the lowest tolerance for the supply-side circuit-breaker
and the highest tolerance for the load side one: an overload of 416 A is presumed in QF2. The current which passes through QF1 will
be 616 A:
Under these conditions, the QF1 E1.2B 1250 supply-side circuit-
breaker trips in a time of 315 s whereas the QF2 T4N 320 load-side
one trips in a slightly longer time of 372 s. For this current value,
selectivity in the overload zone is not guaranteed.
Of course the supply-side circuit-breaker does not trip under 416 A, whereas for sufficiently higher values than 416 A (e.g. 700 A) the
supply-side circuit-breaker trip time is greater than that of the load side one, since the sum of the currents of the other loads ‘weighs’
less on the total current which passes through them.
Finally, assessment of the currents which effectively pass through the circuit-breakers could make selectivity critical for certain overload
current values and in these cases the solution may be to use a higher function L curve.
QF2
T4N 320 PR222DS/P-LSI In320
QF1
E1.2B 1250 Ekip Dip In1250
Ik = 20kA
100 A100 A285 A
10 kA1 kA0.1 kA
T4N 320
616A416A
372s
315s
E1.2B
102s
10s
1s
10-1s
10-2s
103s
104s
Time-Current Curve
AppendixC

Appendix D
Further considerations about the real
currents which circulate in the circuit-
breakers
As mentioned on page 5 of this publication regarding
the real currents which circulate in the circuit-breakers,
three cases can be noted:
- a single circuit-breaker on the supply side of a single
circuit-breaker on the load side (passed through by the
same current)
- a single circuit-breaker on the supply side of several
A supply-side circuit-breaker of a load-side circuit-breaker
In this case the two circuit-breakers are passed through by the same current both under normal conditions and in the case of overcurrent.
To verify the time-current selectivity in the overload and short-circuit zone, it is therefore sufficient to check that the trip curves of the
two devices have no intersections.
circuit-breakers on the load side (supply-side circuit-
breaker passed through by a current higher than that
of the load-side circuit-breaker)
- two or more circuit-breakers on the supply side and
several circuit-breakers on the load side.
By means of some examples, it is shown how incorrect
determination of the real currents which circulate in the
circuit-breakers can lead to lack of selectivity in the over-
load zone or oversizing of the circuit-breakers to obtain
selectivity in the short-circuit zone.
U
XT4N250 Ekip LS/I In250
L
Vref = 400
LLLN/TN-S
XT4N250 Ekip LS/I In250
-Ls
XT4N250 Ekip LS/I In250 - XT4N250 Ekip LS/I In250
10 kA1 kA0.1 kA
102s
10s
1s
10-1s
10-2s
103s
104s
AppendixD

Let us now suppose that there are overload conditions with the
load L1 absorbing a current of 200A.
Circuit-breaker B1 will therefore be passed through by 200A,
whereas circuit-breaker A will be passed through by 470A (200+
90+ 90+90).
With the settings hypothesised above, there are the conditions
shown in the figure, where both the circuit-breakers trip in a time
of about 50s.
Therefore, with the settings hypothesised, in the case of overload
there will not be selectivity between the couple of circuit-breakers
considered.
In most cases, even not carrying out this analysis, the size and
distribution of the overload between the circuit-breakers allows a
difference in the trip times able to realise time-current selectivity.
By modifying the settings of the supply-side circuit-breaker, for
example by raising the trip time of protection L against overload:
CB A: I1 = 0.92 x 400 = 368A (t1=12s)
Selectivity can be obtained in the overload zone since:
load-side circuit-breaker B trips in about 50s
supply-side circuit-breaker A trips in about 200s.
T4S400 PR221 400 - XT2S TMD
10 kA1 kA0.1 kA
102s
10s
1s
10-1s
10-2s
103s
104s
T4S400 PR221 400 - XT2S TMD
10 kA1 kA0.1 kA
102s
10s
1s
10-1s
10-2s
103s
104s
A supply-side circuit-breaker of several load-side circuit-breakers
This installation is certainly the most frequent in practice.
Having more than one circuit-breaker on the load side, there will be different current values between the supply-side circuit-breaker and
the load-side circuit-breaker towards which selectivity is required.
Therefore the trip time of the load-side circuit-breaker due to an overcurrent must be compared with the trip time of the supply-side
circuit-breaker in correspondence with the sum of all the currents which pass through it.
Example
In the installation in the figure, under normal conditions the supply-side circuit-breaker is passed through by a current of 360A whereas
any outgoing feeder is passed through by 90 A.
Possible settings of the circuit-breaker based on the currents which pass through the circuit-breakers are:
CB A: I1 = 0.92 x 400 = 368A (t1=3s)
CB B: I1 = 0.90 x 100 = 90A
The curves of the circuit-breakers with the settings indicated above are shown in the figure. From an initial analysis, time-current selectivity
would appear to be ensured between the two circuit-breakers.
U
T5S 400 PR221DS-LSI R400
Ib = 360.0 A
Vref = 400
LLLN/TN-S
A
V = 400 V
I”k LLL = 50 kA
XT2S 160
TMD100-1000
B1
Ib = 90.0 A
Iz = 134.0 A
In = 90.0 AL1 L2
XT2S 160
TMD100-1000
B2
Ib = 90.0 A
Iz = 134.0 A
In = 90.0 A L3
XT2S 160
TMD100-1000
B3
Ib = 90.0 A
Iz = 134.0 A
In = 90.0 A L4
XT2S 160
TMD100-1000
B3
Ib = 90.0 A
Iz = 134.0 A
In = 90.0 A
T4S400 PR221 400 - XT2S TMD
10 kA1 kA0.1 kA
102s
10s
1s
10-1s
10-2s
103s
104s
AppendixD

The curves of the two circuit-breakers being examined with the settings indicated above are shown in the figure.
At first glance there would not seem to be time-current selectivity between the two pieces of apparatus.
Since these are circuit-breakers equipped with electronic releases, the trip times of the two devices at the significant currents are verified.
1.2xI3 of the load-side circuit-breaker
IB
= 7500x1.1 = 8250 A tA
= 45 s
which corresponds to a current on A of:
IA
= (8250+1000)/3= 3083 A tB
=174 s
1.05xI1 of the supply-side circuit-breaker
IA
= 1156 x1.05=1214 A tA
= 700 s
which corresponds to a current on B1 of:
IB
= (1214x3) - (1000) =2642 A tB
= 450 s
10 kA1 kA0.1 kA 100 kA
102s
10s
1s
10-1s
10-2s
103s
104s
E1.2B 1250 Ekip Dip LSI 1250 - E2.2N 2500 Ekip Dip LSI 2500
10 kA1 kA0.1 kA 100 kA
102s
10s
1s
10-1s
10-2s
103s
104s
AppendixD
Several circuit-breakers on the supply-side of several load-side circuit-breakers
To carry out a simplified analysis, it must be assumed that the circuit is perfectly symmetrical and therefore that the total current recalled
by the loads is divided into equal parts in the three supply-side circuit-breakers.
Example
Under normal conditions, in the installation in the figure, the supply-side circuit-breakers are passed through by a current of 1000A,
whereas the two outgoing feeders are passed through by 1000A and the other by 2000 A.
In the analysis given here, selectivity between a supply-side circuit-breaker A and the largest outgoing feeder B1 is verified.
Possible settings of the circuit-breakers based on the currents which pass through the apparatus are:
CB A: I1 = 0.925 x 1250 = 1156A (t1=12s)
I2 = 8 x 1250 = 10000A (t2=0.4s)
I3=OFF
CB B1: I1 = 0.80 x 2500 = 2000A (t1=3s)
I2 = 3 x 2500 = 7500A (t1=0.2s)
I3=OFF
Ik = 55 kA
L L
Vn2 = 400 V
Sn = 800 kVA
TM1
E1.2B 1250
Ekip Dip
LSI 1250
CB A
U Vref = 20000 V
Vn2 = 400 V
Sn = 800 kVA
TM2
CB A
Vn2 = 400 V
Sn = 800 kVA
TM3
CB A
E2.2N 2500
Ekip Dip
LSI 2500
CB B1
Sn = 1385.64 kVA
Cosphi = 0.90
In = 2000 A
L1
T7H 1250
PR232/P-LSI
In1250
CB B2
Sn = 692.82 kVA
Cosphi = 0.90
In = 1000 A
L1
E1.2B 1250
Ekip Dip
LSI 1250
E1.2B 1250
Ekip Dip
LSI 1250
10 kA1 kA0.1 kA 100 kA
A
B1
102s
10s
1s
10-1s
10-2s
103s
104s

As can be seen, even if the curves overlap, there is time-current selectivity in the overload zone.
Selection of the Icw must also take into account the real currents circulating in the circuit-breaker.
The A circuit-breakers are passed through by a maximum of:
36kA due to a fault between the circuit-breaker and the transformer
18kA due to a fault on the busbar.
These circuit-breakers must therefore be selected with:
Icu > 36kA as the breaking capacity must be higher than the maximum short-circuit current
Icw > 18kA as time selectivity is only required towards the load-side apparatus.
For possible selectivity towards other load-side apparatus, circuit-breaker B1 must have:
Icw > 55kA.
AppendixD

Glossary
Glossary
* ±.....% = tolerance of the protection
Is ultimate selectivity limit
Icu ultimate short-circuit breaking capacity of a circuit-breaker
Icw rated short-time withstand current
Category A type of circuit-breaker without Icw (indicated for the energy selectivity)
Category B type of circuit-breaker with Icw (indicated for the time selectivity)
In
rated current of a release (this identifies the rated current of the circuit-breaker equipped by
the release in question)
Iu rated uninterrupted current of a circuit-breaker (this identifies the “size” of the circuit-breaker)
I3Max
/ I3min
= maximum/minimum threshold of the protection against instantaneous short-circuit
Example:
- for a modular curve C (Im=5..10In) → I3Max
=10In, I3min
=5In
- for a moulded-case TMD circuit-breaker (Im=10In±20%*) → I3Max
=12In, I3min
=8In
- for function I of an electronic release (I3=10In±10%*) → I3Max
=11In, I3min
=9In
Icc short-circuit current
TMD thermomagnetic release with adjustable thermal and fixed magnetic threshold
TMA thermomagnetic release with adjustable thermal and magnetic threshold
EL electronic release
Function L protection against overload
Function S delayed protection against short-circuit
Funzione I instantaneous protection against short-circuit
Function G protection against earth fault
Function D directional protection against short-circuit
I1 trip threshold of function L
t1 trip time of function L
I2 trip threshold of function S
t2 trip time of function S
I3 trip threshold of function I
I4 trip threshold of the function G
t4 trip time of the function G
I7 trip threshold of the function D
t7 trip time of function D
selectivity time trip time of the electronic release when zone selectivity is enabled and the input locking
signal is not present.
Self-protection protection of the moulded-case circuit-breaker equipped with electronic release allowing
rapid times of fault extinction for currents higher than 10 to 12 times the Iu, even when the
instantaneous protection is set to OFF.
ft (foot) measure of length expressed in feet

1SDC007100G0205-11/2014
Contact us
ABB SACE
A division of ABB S.p.A.
L.V. Breakers
Via Pescaria, 5
24123 Bergamo - Italy
Phone: +39 035 395 111
Fax: +39 035 395 306-433
www.abb.com
The data and illustrations are not binding.
We reserve the right to make changes in the
course of technical development of the product.
Copyright 2011 ABB. All rights reserved.
COVER • INDEX

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