Carbon Brushes Technical Guide

TECHNICALGUIDE
CARBON BRUSHES
FOR MOTORS
AND GENERATORS

2
bon brush?What is a carbo ................................................................... 3
esCarbon brush grade .......................................................................... 99
ons and hardwareapes, dimensionsMain carbon brush sha ......... 18
Recommendations
ushes in machinesfor installing carbon bru ................................ 22
g / commutator filmsVisual guide to slip ring .............................. 24
Mersen’s services ............................................................................... 29
rbon brushes?How to order carb ..................................................... 31
CESAPPENDICE .......................................................................................... 32
Contents
01
02
03
04
05
06
07
The specifications or data contained in present catalogue are only given for information and do
not create any undertakings whatsoever. Any copy, reproduction or translation, either partially
or fully, of these information is subject to the Mersen’s prior written consent.
In addition, due to the continuing improvement of techniques and change of applicable standards,
Mersen is entitled to modify at any time the characteristics and specifications of its products as
described in present catalogue.

3
What is a carbon brush?
(also called “motor brush”)
A carbon brush is a sliding contact used to transmit electrical current from a
static to a rotating part in a motor or generator, and, as regards DC machines,
ensures a spark-free commutation.
A carbon brush can be:
Made of one or more carbon blocks
Equipped with one or more shunts / terminals
Five brush grade families are used for brush manufacturing. Each of them corre-
sponds to a speciﬁc requirement and has its own production process (see pages 9
to 17 of this guide).
SLIP RING AND COMMUTATOR SURFACE CONDITIONS (ROUGHNESS)
A proper slip ring or commutator roughness will give the carbon brush an adequate seating
base and will ensure a good current transmission (See Technical Data Sheet AE-TDS/02*).
Slip ring and commutator surfaces must be neither too smooth (glossy), nor too rough to
enable optimal carbon brush performance.
High mica often creates serious problems for brushes. Commutators therefore have to be
carefully checked (correct mica undercutting, absence of burrs along the bar edges) and
the bar edges have to be properly chamfered (See Technical Data Sheet AE-TDS/03*).
It is also necessary to check that the commutator or slip ring run out does not exceed
acceptable limits.
Operating parameters
The carbon brush plays an essential part in the operation of electrical machines.
To enable it to fulﬁll its function, we need to consider three types of parameters:
Mechanical
Electrical
Physical and chemical (environment)
Considering those parameters, together with technical information supplied by your
teams, our experts will be able to select the most suitable carbon brush grade for
your application. Our teams will also advise you how to optimize the parameters of
your electrical machine and to improve the maintenance operations. This joint effort
between your company and Mersen will contribute to the performance and longevity
of your equipment.
For more information please refer to Technical Data Sheet AE-TDS/01*, “Functions
of a good carbon brush, what you should know”.
Mechanical parameters
*More information can be obtained from our Technical data sheets, sent upon request, and also available from our web site www.mersen.com
01

4
TECHNICAL GUIDE - WHAT IS A CARBON BRUSH?
FRICTION COEFFICIENT (CALLED “ μ ”)
Carbon brush friction coefficient “μ” has to be low and stable over time to allow the carbon
brush to work without overheating.
“μ” has no fixed value. It is the result of many factors depending upon the carbon brush
grade, speed, load, commutator (or slip ring) condition and environment.
For a given carbon brush grade, it is not possible to indicate a precise “μ” value,
only a magnitude. This is sufficient for most machine calculations or projects.
“μ” friction coefficient calculation formula
The “μ” friction coefficient is the relationship between T (tangential force due
to friction) and N (normal force)
VIBRATION
Excessive vibration reduces the quality of the carbon brush / commutator or carbon brush /
slip ring contact, and therefore the overall performance of your equipment.
Vibration can be caused by:
Poor machine balancing, defective bearings, incorrect alignment
Commutators in poor condition (e.g. deformed)
External components of the machine itself (gears, coupling, drive equipment, loads)
Very high or fluctuating friction resulting from an unsuitable carbon brush grade, polluted
atmosphere, extended periods of underload, or insufficient roughness (glazed surface)
Moving machinery (locomotive, mine truck…)
Extreme vibration is likely to cause major brush damage as well as destruction of the
brush-holder and associated commutator or slip ring.
These incidents may be minimized, if not eliminated, by proper brush design and regular
maintenance of the electrical machine.
CARBON BRUSH PRESSURE ON A SLIP RING OR COMMUTATOR
At any given machine speed, the spring pressure must be sufficient such that proper contact
between the carbon brush and the slip ring / commutator is maintained. (See Technical
Data Sheet AE-TDS/11*).
Mersen recommends:
For stationary electrical machines: 180 - 250 g/cm² (2.56 - 3.56 psi)
For electrical machines under heavy vibration (e.g. traction motors): 350 - 500 g/cm²
(5.00 - 7.11 psi)
Equal spring pressure must be maintained for all carbon brushes to ensure a good
current distribution. We therefore advise periodic pressure measurement with a scale
or a load cell.
BRUSH-HOLDERS
The carbon brush has to be guided by a brush-holder of sufficient height and with an ad-
equate clearance to avoid either the brush getting stuck or the brush rattling in the holder.
Tolerances and clearances are set by the International Electrotechnical Committee (I.E.C.).
(See Technical Data Sheet AE-TDS/04*).
μ =
T
N

5
Electrical parameters
FILM
BRUSH
METAL
POINTS OF
CONTACT
INTERFACE
LAYER
VOLTAGE DROP (OR CONTACT DROP)
The voltage drop has to be moderate to avoid overheating and abnormal electrical loss
which can damage the sliding contact. It also influences commutation and current distribu-
tion in between the carbon brushes.
This is an important characteristic which depends on the carbon brush grade, electrical
contact and film (which is a complex mix of metal oxides, carbon, and water, deposited
on the slip ring or commutator).
It is therefore to be expected that the contact drop is influenced by all the factors which
may modify the film:
Room temperature, pressure and humidity
Environmental impurities
Commutator / slip ring speed
Pressure applied on the carbon brushes
Transverse current
The contact drop data indicated for each of the Mersen carbon brush grades are typical
values obtained in specific operating conditions. They are grouped into five categories
ranging from “extremely low” to “high” (see pages 13 to 15 of this guide).
COMMUTATION (DC MACHINES)
What is Commutation?
Commutation is the process of reversing the direction of the flow of current in
the armature coils under the brush of a DC/AC commutator motor or generator.
The time of commutation is the time taken for complete reversal.
Incorrect adjustment of the brush position relative to the neutral zone, or asymmetrical
brush arm adjustment, can generate commutation sparking, which should not be confused
with other types of sparking due to:
Mechanical causes (vibration)
Winding faults (open or short-circuit)
Poor commutator construction
Quality of the DC supply (ripple or spikes) from the electronic static converters…
Some solutions can help to improve commutation:
Multi wafer carbon brushes
Dual grade composite carbon brushes (with wafers made of different grades)
Sandwich brushes (with two layers of the same grade), which limit cross currents,
and have a positive influence on film control. The wafers are glued. (See Technical
Data Sheet AE-TDS/07*)
Staggering carbon brushes, adapted for large slow machines (See Technical Data
Sheet AE-TDS/09*)
MULTI WAFER BRUSH STAGGERING BRUSHES
Neutral line
SPLIT BRUSH

6
Current density has a major influence on all aspects of brush performance: wear, friction,
and temperature.
The maximum current densities for each grade are those at rated speed. They can vary,
however, depending on the machine’s characteristics and the ventilation method.
Please note that a low current density can be more harmful to the carbon brush and
commutator / slip ring than a high current density (please contact us for more information).
RESISTIVITY
What is resistivity?
The resistivity of a material, usually symbolized by the Greek letter rho (ρ),
represents its resistance to the flow of electrical current.
Higher resistivity materials increase the overall resistance in the commutation circuit,
thereby improving commutation. It is a key parameter in the choice of the suitable carbon
brush grade (please contact us for more information).
Multi wafer brushes, especially sandwich brushes, enable an artificial increase of transverse
resistivity and can improve commutation.
Note
Resistivity values for brush grades indicated in this guide are measured along the radial
direction (please refer to page 18 of this guide for the definition of the radial dimension).
JB
=
I
S x NP
DISTRIBUTION OF CURRENT IN THE BRUSH CONTACT SURFACE
Current does not flow uniformly across the whole brush contact surface. It flows through
a varying number of very small areas called contact spots. Ideally these contact spots are
evenly distributed.
This balance may be disrupted when the contact spots concentrate and decrease in
number. The film will then show signs of grooving, bar marking, streaking, and electrical
erosion, deteriorating over time.
Various factors can cause this imbalance:
External agents (dust, vapors, excessive humidity, temperature)
Unsuitable brush grades for the operating conditions (film too thick, current density too
high or low, poor ventilation…)
Unequal spring pressures causing unequal current distribution between brushes of the
same polarity on commutators and between brushes on the same slip ring.
CURRENT DENSITY
What is current density?
This is the ratio of the current to the cross-sectional area of the brush.
Its symbol is JBrush
.
I = the armature or rotor current flowing through the machine (Amps)
S = carbon brush cross-sectional area (cm² or in²)
NP
= number of carbon brushes (half the number of carbon brushes
for a DC machine)
or number of carbon brushes per slip ring for a slip ring machine

7
HUMIDITY
Water, the essential component of commutator or slip ring films, is supplied by ambient
air. The film will form best in a humidity range of 8 to 15 g / m3
(0.008 to 0.015 oz/ft3) of
air (See Technical Data Sheet AE-TDS/17*).
In very dry air, the film consists mostly of metal oxides, causing high friction and brush wear.
These unfavorable conditions become critical when the absolute humidity rate falls below
a threshold of 2 g / m3 (0.002 oz/ft3) of air.
This may be the case for:
Aerospace and space industry, where machines are likely to operate in rarefied atmo-
spheres at high altitudes
Machines with brushes working in an enclosure filled with dry gas (hydrogen or nitrogen)
Totally enclosed motors (IP 55)
Desert or arctic environments (for example ski lifts)
Mersen proposes carbon brushes with special treatments for these particular applications.
Do not hesitate to consult us.
CORROSIVE VAPORS OR GASES
Even when present in low concentrations, and especially in humid conditions, corrosive
vapors or gases affect and destroy the contact film, damage the commutator (or the ring)
and consequently the carbon brushes.
Examples of corrosive vapors or gases:
Chlorine and its compounds (chlorate solvents)
Ammonia
Hydrogen sulphide
Sulphur dioxide
Products originating from hot distillation of silicones
Mersen’s treated brushes can help mitigate
these problems by creating a protective film
on the contact surface
OILS AND HYDROCARBONS
Commutators, slip rings and carbon brushes can get contaminated by oils and fats from
various origins:
Leaks from a bearing which is not properly sealed
Tiny drops or mist carried by ventilating air
Vapor condensation (developed at hot points)
These oily contaminations disturb the operation of carbon brushes in electrical machines,
leading to the:
lmmobilization of brushes in their holders by the sticky mixture of oil and carbon dust
Deterioration of slip rings, commutators and brush performance as a result of thick
insulating films on the contact surfaces
Physical and chemical parameters (environment)

8
DUST
The more abrasive the dust, the more harmful it is. Dust causes:
Grooving of commutators and slip rings
High brush wear
Carbon brush side gulling (see picture opposite), with brushes sticking in their holders
Pollution of machines
Dust grooves partly avoid these problems, but the best remedy is prevention, providing
clean filtered air to the machines.
In totally enclosed machines, where carbon dust is continuously recirculated, the
same problems are likely to arise, with the possibility of polluting the machine and
decreasing its insulation resistance. These machines should be cleaned regularly.
Mersen is able to design and supply a modular carbon dust collection system extracting
dust at its source to refrain it from dispersing all over the machine (see box below).
Mersen is well aware of how vital it is to control these process parameters,
and can propose maintenance services, in particular in situ diagnostics and
recommendations on your machines.
See page 29 of this guide.
A NEW INNOVATION
PATENTED BY MERSEN
Dust extraction system
integral to the brush-holder
No generator modification
required
Simple installation
Standard product that can
be customized
A complete solution
For original equipment or
retrofit

Carbon brush grades
As stated in this guide’s introduction, there are five main brush grade families, each
with a distinct set of properties.
Some of these groups are complemented by a subgroup of impregnated brush
materials (please consult us to find out more about the specific properties of those
special materials).
The choice of the most suited brush grade depends on a large number of parameters
linked to the machine itself as well as its environment. Choosing the brush grade that
performs best for a specific application requires an in-depth knowledge of its working
environment. Mersen therefore recommends contacting our experts for assistance
with your specific needs.
Mersen has developed a wide range of brush grades able to meet even the most
demanding requirements.
Hereafter, you will find a description of the manufacturing process of our main grade
families, as well as a table with their material properties (see table pages 14 and 15).
You will find on pages 16 and 17 a summary of the major applications together with
the operating limitations of most of the grade families (based on our usual conventions
reminded page 13).
9
02
Grade families
How are our electrographitic brush materials manufactured?
Electrographitic materials are carbographitic materials that are graphitized at
temperatures in excess of 2,500°C in order to transform basic amorphous carbon
into artificial graphite.
MAIN CHARACTERISTICS
Electrographitic brushes have a medium contact drop and low to medium friction
coefficient, and therefore have low electrical loss, particularly suited to high peripheral speeds
(≤ 50 m/s). The graphitization process yields a high strength, low resistance material,
particularly resistant to high temperatures.
MAIN APPLICATIONS
All DC stationary or traction industrial machines, operating with low, medium or high
voltage and constant or variable loads. They are also found on AC synchronous and
asynchronous slip ring applications.
OPERATING LIMITATIONS
Current density in the brushes:
• 8 to 12 A/cm2
(50 to 75 A/in²) under steady conditions
• 20 to 25 A/cm2
(130 to 160 A/in²) for peak loads
Maximum peripheral speed: 50 m/s (154 ft/s).
EG. Electrographitic brushes

10
TECHNICAL GUIDE - CARBON BRUSH GRADES
How are soft graphite brush materials manufactured?
The main ingredients are purified natural graphite and artificial graphite, mixed with
additives, agglomerated with appropriate binders, and treated at a high temperature
to carbonize the binder.
LFC brushes have a low Shore hardness with excellent shock absorbing properties.
This allows them to work in applications where other materials would fail. They excel at
high peripheral speeds which amplify the mechanical stresses associated with friction,
vibration, air flow, run out, and heat.
MAIN APPLICATIONS
Steel and stainless steel slip rings for synchronous machines.
Current density in the carbon brushes: 10 to 13 A/cm² (71 to 84 A/in²)
Maximum peripheral speed: up to 90 m/s (295 ft/s)
LFC. Soft graphite brushes (LFC = Low Friction Coefficient)
How are our carbographitic brush materials manufactured?
They are made from a mixture of coke and graphite powders, agglomerated
with pitch or resin. This powder is molded into blocks which are baked at high
temperature to convert the binder into coke. These materials are not graphitized.
Carbographitic brushes commutate well due to their high resistance and provide good pol-
ishing action, while maintaining moderate contact drop.As a result of their high temperature
treatment, carbographitic brushes can withstand both high temperatures and variable loads.
MAIN APPLICATIONS
Machines with an older design, mostly characterized by a slow speed, lack of interpoles,
generally operating at low voltage
Modern small machines, operating with permanent magnets, servomotors, and universal
motors
Low voltage battery powered motors
Current density in the brushes: 8 to 16A/cm² (50 to 100A/in²) depending on the application
Maximum peripheral speed: 25 m/s (82 ft/s)
A. Carbographitic brushes

11
OVERVIEW OF THE MANUFACTURE OF ELECTROGRAPHITE
BG. Resin-bonded (bakelite graphite) brushes
How are resin-bonded brush grades manufactured?
Powdered natural or artiﬁcial graphite is mixed with a thermo-setting resin.
The mix is then pressed and polymerized at a suitable temperature.
Carbon brushes with high to very high electrical resistance, contact drop, electrical loss,
and mechanical strength, which have very good commutating and cleaning properties.
They can also work at very low current densities.
MAIN APPLICATIONS
AC Schrage-type commutator motors
Medium-speed DC machines at medium voltage
Resin-bonded grades should not be used at higher than rated current
Admissible peripheral speed: 40 m/s (131 ft/s)

12
12
CG-MC-CA. Metal-graphite brushes
How are metal-graphite brush grades manufactured?
Powdered natural or artiﬁcial graphite is mixed with a thermo-setting resin, copper
powder, and/or other metal powders. The mix is then pressed and polymerized
at a suitable temperature in an inert atmosphere.
These metal-graphite materials also include EG and A carbon brushes that are metal-
impregnated (see metal-impregnated brush grades on page 15).
Dense to very dense carbon brushes with low friction and very low contact drop, therefore
operating with very low losses and high currents.
(CG) Copper-based brush grades
MAIN APPLICATIONS
Low-speed, low voltage DC machines
Medium-speed, highly-loaded AC asynchronous machines (wind turbine generators)
Medium-speed AC synchronous motors slip rings
High current collection systems (electrolytic treatment lines, wire annealers, galvanizing
lines…)
Low-voltage current collection (military, medical, paramedical, signal…)
Special machines
Slip ring assemblies in rotary joints
Current density:
• 10 to 30 A/cm² (75 to 200 A/in²) under steady conditions
• Up to 100 A/cm² (660 A/in²) for peak loads, depending on metal content
Peripheral speed: up to 35 m/s (115 ft/s), depending on metal content
(CA/SG) Silver-based brush grades:
Silver grades have a higher conductivity than copper grades and form a special low-
resistance ﬁlm due to the conductivity of silver oxide. Silver grades can also transfer low
voltage current signals without degradation.
MAIN APPLICATIONS
Signal current transmission (thermocouples, thermometric sensors, regulation…)
Pulse transmission to rotating devices (radar, prospection…)
Tachometer generators
Aerospace and space applications
Shaft grounding in a dual-grade construction
Current density up to 50 A/cm² (440 A/in²).
Peripheral speed: up to 25 m/s (82 ft/s)
Dense to ver
operating with

13
13
The contact drop and friction values are given
in the following table:
The contact drop and friction values were measured
on a copper commutator in the following laboratory
conditions:
The current density and peripheral speed operating conditions were derived from observations on actual machines
in good working order and operating in normal conditions.
DETAILS ON CONTACT DROP AND FRICTION (SEE TABLES FOLLOWING PAGES)
Symbol Signification
Contact
drop
(Sum of
both
polarities)
Friction
µ
H High > 3 V μ > 0.20
M Medium 2.3 V - 3 V 0.12 < μ < 0.20
L Low 1.4 V - 2.3 V μ < 0.12
VL Very low 0.5 V - 1.4 V
EL Extremely low < 0.5 V
Elements Contact drop Friction µ
Current type DC DC
Current density
10 A/cm²
(130 A/in²)
10 A/cm²
(130 A/in²)
Speed 12.5 m/s (41 ft/s) 25 m/s (82 ft/s)
Spring pressure 18 kPa (2.6 PSI) 18 kPa (2.6 PSI)
Temperature
65-70°C
(149-158°F)
65-70°C
(149-158°F)
Brush type radial radial
Consolidation of carbon brush grades
An increasing number of companies wish to reduce the number of brush grades and
carbon brush types they currently use. Mersen will assist in meeting these expectations.
For many simple applications, this is quite easy as many different brush grades will
perform well.
Difficult machines, however, will require careful preliminary examination. Mersen therefore
recommends that our customers contact the Customer Technical Assistance to correctly
select the brush grade to be used for each specific case.
Our Customer Technical Assistance Service is at your disposal
for any question
Phone: +33 (0)3 22 54 44 90 / Fax: +33 (0)3 22 54 46 08
E-mail: infos.amiens@mersen.com
Mersen is present in over 40 countries around the world; our branches are also at your
disposal for local technical assistance.
You can reach our worldwide network through our website at www.mersen.com

14
14
Brush grade groups main characteristics (according to IEC norm 60413)
BRUSH
GRADE
GROUPS
Grades
Apparent
density
Resistivity
ųΩ.cm
(ųΩ.in)
Shore
hardness
Flexural
strength
MPa
(PSI)
Contact
drop
Friction
Maximum
current
density
A/cm²
(A/in²)
Upper
speed
limit
m/s
(ft/s)
Metal
content
%
EG - Electro-
graphitic
EG34D 1.60
1,100
(433)
40
25
(3,626)
M M
12
(77)
50
(164)
/
EG389P 1.49
1,600
(630)
29
19
(2,756)
M M
12
(77)
50
(164)
/
L1 1.61
1,270
(500)
35
21
(3,046)
M M
12
(77)
60
(197)
/
EG362 1.60
2,500
(984)
35
21
(3,046)
M M
12
(77)
50
(164)
/
EG40P 1.62
3,200
(1,260)
57
27
(3,916)
M M
12
(77)
50
(164)
/
EG313 1.66
5,000
(1,968)
50
21
(3,046)
M L
12
(77)
50
(164)
/
EG367 1.53
4,100
(1,614)
52
21
(3,046)
M M
12
(77)
50
(164)
/
EG387 1.60
3,500
(1,378)
60
31
(4,496)
M M
12
(77)
50
(164)
/
EG300H 1.57
4,100
(1,614)
60
26
(3,771)
M L/M
12
(77)
50
(164)
/
2192 1.56
5,100
(2,008)
55
23
(3,336)
M M
12
(77)
50
(164)
/
CB377 1.71
6,350
(2,500)
75
29
(4,206)
H L
12
(77)
40
(131)
/
EG319P 1.46
7,200
(2,835)
52
26
(3,771)
H M
12
(77)
50
(164)
/
EG365 1.62
5,300
(2,087)
40
15
(2,176)
M M
12
(77)
50
(164)
/
Impregnated
electro-
graphitic
EG7099 1.72
1,100
(433)
40
34
(4,931)
M M
12
(77)
45
(148)
/
EG9599 1.61
1,600
(630)
33
28
(4,061)
M M
12
(77)
45
(148)
/
EG9117 1.69
3,300
(1,299)
77
36
(5,221)
M M
12
(77)
50
(164)
/
EG8019 1.77
4,700
(1,850)
77
31
(4,496)
M M
12
(77)
45
(148)
/
CB86 1.64
4,830
(1,902)
65
29
(4,206)
M M
12
(77)
50
(164)
/
2189 1.63
6,100
(2,401)
60
32
(4,641)
M M
12
(77)
50
(164)
/
510 1.44
7,100
(2,795)
45
17
(2,466)
M M
12
(77)
50
(164)
/
535 1.53
7,100
(2,795)
55
26
(3,771)
M M
12
(77)
50
(164)
/
EG8067 1.67
3,900
(1,535)
77
36
(5,221)
M M
12
(77)
45
(148)
/
AC137 1.72
5,100
(2,008)
80
41
(5,947)
M M
12
(77)
50
(164)
/
168 1.58
7,100
(2,795)
65
36
(5,221)
M M
12
(77)
50
(164)
/
EG8220 1.82
5,000
(1,968)
90
48
(6,962)
M M
12
(77)
50
(164)
/
EG7097 1.68
4,000
(1,575)
80
35
(5,076)
M M
12
(77)
50
(164)
/
EG341 1.57
7,200
(2,835)
74
34
(4,931)
H M
12
(77)
50
(164)
/
EG7655 1.70
5,600
(2,205)
68
33
(4,786)
M M
12
(77)
50
(164)
/
EG6754 1.76
4,150
(1,634)
87
40
(5,802)
M M
12
(77)
50
(164)
/

15
15
BRUSH
GRADE
GROUPS
Grades
Apparent
density
Resistivity
ųΩ.cm
(ųΩ.in)
Shore
hardness
Flexural
strength
MPa
(PSI)
Contact
drop
Friction
Maximum
current
density
A/cm²
(A/in²)
Upper
speed
limit
m/s
(ft/s)
Metal
content
%
A - Carbo-
graphitic
A121 1.75
2,250
(886)
30
26
(3,771)
M L
12 to 20
(75 to125)
≤ 15
(≤ 49)
/
A176 1.60
52,500
(20,669)
40
20
(2,901)
H L
8 to 10
(50 to 65)
30
(98)
/
A252 1.57
45,000
(17,716)
27
16
(2,321)
H L
10 to 12
(65 to 75)
≤ 25
(≤ 82)
/
M44A 1.64
3,050
(1,201)
50
26
(3,771)
M M
10
(65)
≤ 25
(≤ 82)
/
LFC -
Soft graphite
brushes
LFC501 1.46
1,900
(748)
10
8
(1,160)
M L
6 to 10
(40 to 65)
75
(246)
/
LFC554 1.26
2,000
(787)
12
11
(1,595)
M L
11 to 13
(71 to 84)
90
(295)
/
BG -
Resin-graphite
BG412 1.82
13,800
(5,433)
/
36
(5,221)
H M
8 to 10
(51 to 65)
35
(115)
/
BG469 1.80
9,450
(3,720)
/
35
(5,076)
H M
6 to 8
(40 to 50)
35
(115)
/
BG348 1.50
25,500
(10,039)
/
25
(3,626)
H M
8 to 10
(51 to 65)
40
(131)
/
CG - MC -
Metal-graphite
COPPER
AGGLOMERATED
C6958 2.50
350
(138)
/
30
(4,351)
VL M
10 to 25
(65 to 220)
≤ 32
(≤ 105)
25
C7788 2.80
300
(118)
/
25
(3,626)
M M
12 to 20
(75 to 125)
40
(131)
43
CG651 2.95
130
(51)
/
30
(4,351)
VL L
12 to 14
(75 to 90)
35
(115)
49
CG626 2.88
180
(71)
/
45
(6,527)
VL L
12 to 15
(75 to 100)
30
(98)
49
MC79P 5.15
8
(3)
/
98
(14,214)
EL L/M
25 to 30
(160 to 200)
20
(66)
83
CG657 4.00
35
(14)
/
65
(9,427)
VL M
12 to 20
(75 to 125)
30
(98)
65
CG757 4.50
35
(14)
/
45
(6,527)
VL M
16
(103)
25
(82)
75
CG857 5.65
7.5
(3)
/
77,5
(11,240)
EL M
20 to 30
(129 to 194)
20
(66)
91
CG957 5.45
40
(16)
/
110
(15,964)
EL M
20 to 30
(129 to 194)
20
(66)
87
MC877 5.40
12.5
(5)
/
89
(12,908)
EL M
20 to 30
(129 to 194)
20
(66)
87
CA -
Metal-graphite
SILVER
AGGLOMERATED
CA38 2.55
250
(98)
/
10
(1,450)
EL M *
25
(82)
33
CA26 3.60
20
(8)
/
40
(5,802)
EL M *
20
(66)
60
CA28 4.00
40
(16)
/
45
(6,527)
EL M
20 to 30
(129 to 194)
20
(66)
65
CA10 8.00
6.5
(3)
/
160
(23,206)
EL M *
15
(49)
93
Metal-graphite
METAL
IMPREGNATED
M609 2.65
310
(122)
35
33
(4,786)
VL/EL EL
12 to 15
(75 to 100)
35
(115)
45
M673 1.72
1,180
(465)
35
26
(3,771)
EL H
10 to 12
(65 to 75)
40
(131)
5.5
M9426 1.62
1,775
(699)
24
20
(2,901)
VL M
12 to 15
(75 to 100)
30/45
(98/148)
9
M621 3.00
400
(157)
34
35
(5,076)
EL M
40
(267)
40
(131)
44
M9020 1.75
2,700
(1,063)
68
37
(5,366)
L M
12 to 15
(75 to 100)
45
(148)
5
M8295 1.80
1,775
(699)
54
34
(4,931)
VL M
12 to 15
(75 to 100)
30/45
(98/148)
9
MA7696 3.00
250
(98)
/
33
(4,786)
VL M
12 to 15
(75 to 100)
35
(115)
55
Note:1MPa(megapascal)=10daN/cm²(decanewton/cm²)and1kPa(kilopascal)=10cN/cm²(centinewton/cm²).
*Pleasecontactus(mAlowcurrent)

16
Type of current / Application
Current
density
A/cm²
(A/in²)
Speed
m/s
(ft/s)
Pressure
kPa
(PSI)
Brush grades
DIRECT CURRENT
Old machines without interpoles
All motors 6
(40)
15
(49)
18
(2.6) EG40P - A176 - EG34D
Low voltage machines (any power)
Marine turbo-alternator exciters
30 to 50 V
4 - 8
(25 - 50)
25
(82)
18
(2.6) LFC3H - EG7099 - CG651 - A121
Welding group generators
30 to 50 V
0 - 20
(0 - 125)
< 20
(< 65)
18
(2.6) EG389P - EG367 - EG313
Industrial machines (110 - 750 V)
Motors for general applications
(high speeds)
8 - 12
(51 - 77)
20 - 45
(65 - 148)
18
(2.6) EG34D - EG313 - EG367 - EG389P
Hydro turbo-alternator exciters 8 - 12
(51 - 77)
< 20
(< 65)
18
(2.6)
EG34D - EG7099 - EDG389P
EG9599 - EG365
Thermal turbo-alternator exciters 8 - 10
(51 - 65)
35 - 50
(115 - 164)
18
(2.6) EG367 - EG365 - EG9599 - EG389P
Pilot exciters 2 - 5
(13 - 33)
< 35
(< 115)
18
(2.6) EG34D - EG389P - BG469
Amplidynes 4 - 12
(25 - 77)
25
(82)
18
(2.6) EG34D - EG389P
Illgner and Ward Leonard
generators (any speed)
4 - 12
(25 - 77)
20 - 35
(65 - 115)
18
(2.6) EG389P - EG367 - EG313
Paper mill motors
and generators
4 - 12
(25 - 77)
35
(115)
18
(2.6)
EG34D - EG9599 - EG7099 - EG34D
EG389P - BG469 - EG313 - 168
Marine generators 4 - 12
(25 - 77)
20 - 35
(65 - 115)
18
(2.6) EG34D - EG389P - EG7099 - EG313
Rolling mill reversing motors 8 - 20
(51 - 125)
0 - 15
(0 - 49)
18
(2.6) EG319P - EG369 - EG313 - 2192 - 535 - 510
Rolling mill roughing motors 8 - 15
(51 - 100)
20 - 35
(65 - 115)
18
(2.6)
EG389P - EG40P - EG319P - EG6489
EG313 - EG365 - 2192 - CB86
Mine winder motors 12
(77)
25
(82)
18
(2.6) EG313 - EG365 - EG367 - CB377
Totally enclosed motors 10-12
(65 - 77)
18
(2.6) EG9117 - EG8067 - EG7593
ALTERNATING CURRENT
Single phase and repulsion
motors
8
(51)
5 - 15
(16 - 49)
18
(2.6) A252 - EG367
Schrage-type three-phase motors 8 - 12
(51 - 77)
5 - 35
(16 - 115)
18
(2.6) BG412 - BG469 - BG348 - EG367
Schorch-type three-phase motors 10 - 14
(65 - 90)
5 - 35
(16 - 115)
18
(2.6) BG28 - BG469 - EG367 - BG348
Scherbius machines 7 - 9
(45 - 58)
30
(98)
18
(2.6) EG389P - EG313 - LFC554 - EG362
“Stationary” commutator machines
Grade selection based on application
Mersen has developed a wide range of carbon grades to meet even the most demanding applications. We recommend that our
customers contact the Customer TechnicalAssistance to correctly select the most suitable grade for each speciﬁc application.
The tables below detail brush grades most suited for different applications and operating conditions (current density, peripheral
speed and applied brush pressure).
For each machine group, the most common brush grades are listed.
The order of the brush grades in the table does not imply a ranking of their performance
Never mix different brush grades on a slip ring or commutator.

17
Type of current /
Application
Slip ring
material
Current density
A/cm² (A/in²)
Speed
m/s (ft/s)
Pressure
kPa (PSI)
Brush grades
Earth Return Current Units (ERCU)
All Steel-Bronze 0 - 30 (0 - 194) 3 - 8 (10 - 26) 35 - 40 (5 - 5.8) MC877 - MC79P
DIRECT CURRENT
Pickling / Tinning rolls Bronze 20 - 30 (125 - 194) 3 (10) 18 - 40 (2.6 - 5.8) MC79P - CG957
Syn-
chronous
machines
(grooved
or plain
slip rings)
3 000 rpm
Stainless steel 11 - 13 (62 - 85) ≤ 100 (≤ 328) 13 - 18 (1.9 - 2.6) LFC554
Steel 6 - 10 (39 - 65)
≤ 70 - 80
(≤ 230 - 262)
15 - 18 (2.2 - 2.6) LFC501
1 500 rpm Steel-Bronze 8 - 12 (51 - 77) ≤ 40 (≤ 131) 18 (2.6)
CG651 - CG657 (Bronze)
EG34D - EG389P
L1 (Steel)
≤ 500 rpm Cast iron 6 - 10 (39 - 65) ≤ 20 (≤ 66) 18 (2.6) EG34D - EG389P - L1
Equalizers in hydrogen Steel-Bronze 5 - 8 (33 - 52) 25 (82) 18 (2.6) EG34D - EG9599 - M9426
ALTERNATING CURRENT
Asyn-
chronous
machines
Open type Steel-Bronze 12 - 16 (78 - 104) 15 - 25 (49 - 82) 18 (2.6)
CG651 - EG34D - EG389P
CG657
Totally
enclosed type
Steel-Cupronickel 6 - 8 (39 - 52) 15 - 25 (49 - 82) 18 (2.6) EG34D
Motors with carbon
brush lifting device
Steel-Bronze 25 - 30 (163 - 195) 20 - 25 (66 - 82) 18 (2.6) MC79P - CG957
High-speed
asynchronous
(pumps, ventilators)
Bronze 8 - 10 (52 - 65) ≤ 50 (≤ 164) 18 (2.6) EG389P - EG34D - M9426
Synchronous
induction machines
Bronze 8 - 12 (51 - 77) 15 - 40 (49 - 131) 18 (2.6) M673 - M9426
Wind power generators Steel-Carbon 12 - 15 (78 - 98) 45 (148) 18 (2.6) M8285 - M9426 - CG626
Slip ring machines
Type of current /
Application
Current density
A/cm² (A/in²)
Speed
m/s (ft/s)
Pressure
kPa (PSI)
Brush grades
DIRECT CURRENT
Light traction
All motors 8 - 12 (51 - 77) 40 - 50 (131 - 164) 30 - 40 (4.4 - 5.8) EG34D - EG7099 - EG387 - EG9599 - EG8067
Heavy traction
Old motors 10 - 12 (65 - 77) < 45 (< 148) < 35 (< 5) EG34D
Modern motors > 12 (> 77) > 45 (> 148) 35 (5)
EG300H - EG9117 - EG387 - EG8067
EG7097 - EG6754 - EG8220
Diesel-electric traction (locomotives and electric trucks)
Generators 10 - 14 (65 - 91) 40 (131) 25 (3.6) EG389P - EG7099 - EG8067 - AC137
Alternators (excitation) 8 - 12 (51 - 77) < 50 (< 164) 22 (3.2) EG34D - EG389P - L1
Motors 15 (100) 45 (148) 35 (5) EG7099 - EG8067 - EG7097 - EG6754 - EG8220
Fork lift truck and hoisting motors (low voltage)
Open type (handling) 15 - 20 (100 - 130) 10 - 25 (33 - 82) 35 (5) A121 - M621 - C7788
RECTIFIED CURRENT
Heavy traction
Modern motors 12 - 15 (77 - 100) 50 (164) 35 (5) EG367 - EG300H - EG8067 - EG7097 - EG6754
ALTERNATING CURRENT
16 and 50 Hz heavy traction
Motors 12 - 16 (77 - 104) 45 (148) 25 (3.6) EG367 - E8067 - EG7097
“Traction” commutator machines
2
3

a
a
r
r
tt
18
18
Main carbon brush types,
dimensions and hardware
When contacting us regarding your brush requirement, please provide the following:
Dimensions in “t” x “a” x “r” (IEC norm 60136).
- where “t” is the tangential dimension or “thickness”
- “a” is the axial dimension or “width”
- and “r” is the radial dimension or “length”’.
The “r” dimension may be for information only.
The same rule applies whether this is a commutator or slip ring brush.
Be careful in specifying the unit of measurement as imperial and metric units may
be easily confused (1” = 25.4 mm, is not the same as 25 mm).
“t”, “a” and “r” dimensions
Orientation of a carbon brush on a commutator or on a slip ring
NORMAL ORIENTATION
OF A CARBON BRUSH
ON A COMMUTATOR
NORMAL ORIENTATION
OF A CARBON BRUSH
ON A SLIP RING
COMMUTATOR SLIP RING
03

CANTILEVER TOP
19
19
BOTTOM BEVEL
(See Technical Data Sheet AE-TDS/16*)
RADIUS RADIUS + BEVEL
BEVELLED TOP ROUNDED TOP
WITH FLAT PART
GUIDING HOLE
PLAIN BRUSH
Standard brush conﬁgurations
CARBON BRUSH TOPS (COMMON SHAPES)
CARBON BRUSH SIDE EDGES
CARBON BRUSH CONTACT SURFACE
Slots and holes dimensions Standardized values L (mm)
SPADE TERMINAL FLAG TERMINAL DOUBLE SHOE
TERMINAL
bolt ø (mm) 3 4 5 6 8 10
d (mm) 3.4 4.3 5.2 6.5 8.5 10.5
16 - 20 - 25 - 32 - 40 - 50 - 56 - 63 - 71
80 - 90 - 100 - 112 - 125 - 140 - 160
TERMINAL TYPES AND DIMENSIONS SHUNT LENGTH
TECHNICAL GUIDE - MAIN CARBON BRUSH TYPES, DIMENSIONS AND HARDWARE
NON-REVERSING
CHAMFER
LIMIT WEAR
STOP HOOK
Types of hardware
α
α
βββ
R
CONCAVE / CONVEX TOP
R R
RGROOVED TOP

20
20 Shock
absorber
material
Hard material
Mounting methods
GLUED SHOCK ABSORBER
BRUSH WITH REMOVABLE TOP
FOR TINNING ROLLS DUST GROOVES AND RECESSES
SCHOCK
ABSORBER AND
HARD MATERIAL
FIXED PLATE SILESS
WEAR LIMITING
PLASTIC CLIPS
TOP PLATE
FOR CANTILEVER
PRESSURE DEVICE
BRUSH WITH
ALARM SHUNT
SCHOCK ABSORBER
AND HARD PLATE
(THE TWO PLATES
ARE THREADED
ON TWO FLEXIBLES
AND NOT GLUED)
SANDWICH BRUSH*
(2 EG LAYERS)
CROSS GROOVED
CONTACT FACE
GLUED BRUSH*
1 EG LAYER
1 BG LAYER
DUAL GRADE
COMPOSITE BRUSH
FOR SLIP RING*
1/3 EG LAYER
2/3 CG LAYER
CONTACT FACE
WITH SAW CUT
HARD INSULATING TOP
(RECESSED AND GLUED)
Reinforced
steel plates
Single brushes Split brush
Alarm shunt
Glueing Glueing Glueing
*See Technical Data Sheet AE-TDS/07, sent upon request, and also available from our web site www.mersen.com
Shock
absorber
material
Hard material

21
Shunts
MAIN SHUNT / CARBON BRUSH FASTENING METHODS
Shunt diameters follow the industry standard as indicated below:
All shunts are available with tinned wires for corrosion protection.
Tamping:
Conductive powder tamped
mechanically into the hole
around the shunt.
Riveting:
Process used for specific applications
(e.g. aviation). The shunt loop placed
into the carbon brush is preformed with
a tool before the riveting operation.
Diameter
(mm)
1.6 1.8 2 2.2 2.5 2.8 3.2 3.6 4 4.5 5 5.6 6.3
Nominal value
of current (A)
15 17 20 24 28 32 38 44 50 60 75 85 100
21
Hardware for split brushes
GLUED RUBBER PAD
SHOCK ABSORBER PLATE AND HARD TOP PLATE
FIG. 1 FIG. 2 FIG. 3
This pad is symmetrical, allowing bi-
directional rotation. However, pressure is
located at the contact point of the spring.
Furthermore the high friction coefficient
of the power pad keeps the spring from
sliding freely on the brush top and creates
lateral forces.
This is the most common mounting type.
Placed directly on the carbon brush, the
shock absorber plate is topped by a hard
non-metallic plate. These two elements
are kept in place by threading the shunts
through them. They can either be indepen-
dent (Fig. 4) or glued to each other and
the carbon brush (Fig. 5 and 6). Depend-
ing on the shape of the spring, the hard
top plate can be machined with a convex
(Fig. 7) or concave profile (Fig. 8).
FIG. 4 FIG. 6
FIG. 7 FIG. 8
FIG. 5

FIG. 2
FIG. 1
Make sure that the brush-holder is in working condition and check the interior surface
condition.
Adjust the distance between brush-holder and commutator to range from 2.5 to 3 mm
(Fig. 2).
Align the carbon brushes parallel to the commutator bars.
Check with an appropriate gauge that the pressures are equal on all the carbon brushes.
Recommendations for installing
carbon brushes in machines
Our recommendations are as follows:
Do not mix different carbon brush grades on a machine to avoid serious problems.
Make sure to remove the existing film before any carbon brush grade change.
Check that the carbon brushes slide freely in their brush-holders without excess
clearance (see Technical Data Sheet AE-TDS/04*).
Check that the carbon brushes were not fitted (or re-fitted) in the wrong direction in
the brush-holders. This is especially crucial for carbon brushes with a bevelled contact
surface or split brushes with a metal plate.
To precisely match the carbon brush contact surface to the slip ring or commutator radius,
use brush-seating stones (pumice stones) while running at low or no load. Seating stone
dust rapidly erodes the brush contact surface to the right curvature.
It is of course essential to use the “M” (Medium grain) grade of grinding stone again after
this operation.
When a lot of carbon brush material has to be removed, first rough-grind the surface us-
ing 60 or 80-grit sandpaper. To do this, just insert it with the abrasive face up between
the contact surface and the commutator, and move it back and forth as shown in Fig. 1.
After brush seating thoroughly clean the contact surfaces, blowing away any abrasive
material and/or carbon brush dust.
Carbon brushes
Carbon brush contact surface seating
Brush-holders
22
04

23
TECHNICAL GUIDE - RECOMMENDATIONS FOR INSTALLING CARBON BRUSHES IN MACHINES
Grade groups
On slip ring
kPa (PSI)
On commutator
Stationary
machines
kPa (PSI)
Traction
machines
kPa (PSI)
Electrographite 18 - 20
(2.6 - 2.9)
18 - 20
(2.6 - 2.9)
35 - 45
(5.1 - 6.5)
Resin-impregnated electrographite 18 - 25
(2.6 - 3.6)
35 - 55
(5.1 - 8)
Carbographitic & Resin-bonded 18 - 20
(2.6 - 2.9)
n/a
Soft graphite 11 - 20*
(1.6 - 2.9)
Metal-graphite
Normal speeds 18 - 20
(2.6 - 2.9)
Speeds < 1 m/s 25 - 27
(3.6 - 3.9)
RECOMMENDED PRESSURES
IN NORMAL WORKING CONDITIONS
*Pleaseconsultus
Note : 1 kPa = 10 cN/cm² (centinewton/cm²) = 0.145 PSI, and is close to 10 g/cm².
Check that there is no out-of-round above 3 mils (75 μm) or any obvious surface defect (see
Technical Data SheetAE-TDS/02*). If needed, grind or machine using a tool support frame.
Mill or undercut the commutator slots (Fig. 1).
Chamfer the bar edges 0.2 to 0.5 mm at 45° (Fig. 2).
Clean the surface with an “M” grade of grinding stone. Avoid the use of abrasive paper or
cloth. It is absolutely necessary to have sufﬁcient roughness (1.3 to 2 μm Ra) in order to
create and maintain a correct ﬁlm.
Ourexpertsareatyourserviceforanyon-sitediagnostic,maintenance,orrefurbishment.
First make sure that all carbon brushes slide freely inside the brush-holders, the shunts
are correctly routed, and the terminals are properly tightened. Then start up the machine,
preferably at low load, and increase progressively until full load is reached.
Commutators and slip rings
Putting the machine into service
FIG. 2
FIG. 1

24
24
COLOR INTENSITY
P2 - P4 - P6: Normal films
Uniform, light brown (P2) to darker brown (P6).
The machine and the carbon brushes work well.
P. Film types
Visual guide to slip ring /
commutator films
Technical Data Sheet AE-TDS/13
The film is a complex mix of metal oxides, carbon and water, which is deposited on the
collector / slip ring. A close look at the film can help in assessing the condition of your
electrical rotating machine.
Below are examples of various film conditions and commutator / slip ring faults, as well
as their causes.
P2 P4 P6
SUITABLE FILMS
05

25
25
TECHNICAL GUIDE - VISUAL GUIDE TO SLIP RING / COMMUTATOR FILMS
P14aP12 P14b
P14FF*P14c P16a
P16FF*P16b
CLASSES OF FILM DEPOSIT
P12: Streaky film
Lines or bands of varying width, alternating light and dark, without copper wear.
Most frequent causes: excess humidity, oil vapors or aggressive gases
in the atmosphere, underloaded carbon brushes.
P14: Raw grooved film
Same as for P12, but with copper-colored raw grooved bands or very lightly colored
bands. The metal is being attacked.
Most frequent causes: same as for streaky film, but worsened or longer-lasting. Also
the carbon brush grade may be unsuitable.
P16: Patchy film
Showing spots of various shapes, colors and dimensions, without any pattern.
Most frequent causes: deformed or dirty commutator, out-of-round slip ring.
SUSPECT FILMING REQUIRING MONITORING

26
PATCHINESS DUE TO MECHANICAL CAUSES
P22: Uneven film, “screw thread” effect
Most frequent cause: bad commutator machining during a maintenance operation
(chattering tool).
P24: Dark in patches, often followed by lighter faded patches, signs of commutator
deformation
Most frequent cause: defect affecting one bar or a group of bars, and making the carbon
brush bounce. Light bars are high bars, dark bars are low bars.
P26 - P28: Dark patches in the middle or on the edges
Shading in the middle of the bars (P26) or at the two bar edges (P28).
Most frequent cause: poor maintenance of the commutator.
P22
P42
P26
P24
P44
P28
BAR MARKING DUE TO ELECTRICAL CAUSES
P42: Alternate bars of light and dark
The dark bars have a polished, mat or blackened appearance. This pattern is repeated
all around the whole commutator.
The most frequent causes are of an electrical origin. They appear on armatures with
more than one conductor per slot, and are linked with successive and increasingly difficult
commutation of each successive conductor in the slot.
P44: Pitting - Strong spark marks
Most frequent cause: high frequency current flow.

27
PATCHES DUE TO POLLUTION
P62: Strong presence of deposits (oil, grease) on the film
Most frequent cause: carbon brush contaminated during maintenance operation,
or environmental factors.
PARTICULAR TYPES
T10: Brush image on commutator
T11: Brush image on slip ring
Dark or black mark reproducing the carbon brush contact surface on the commutator /
slip ring.
Most frequent causes: accidental overload or electrolytic mark during a long period
of stoppage.
T12: Dark fringe due to high bar L2
B6: Spark burns at bar edges
B8: Burning at center of bars
B10: Pitted film
Variable number of small light patches randomly spread on a normal filmed track.
Most frequent cause: sparking under the carbon brushes.
B. Burning
T. Marking
P62
B8
T11
B6
T10
B10
T12

28
28
R2 R4
R2: Commutator with axial proﬁle showing metal wear on each track – correct stagger.
This wear may appear after a very long period of operation.
R4: Commutator showing abnormal wear of the metal due to incorrect axial stagger,
unsuitable carbon brush material, various pollutions...
L2: high bar
L4: low bar
L6: high mica
L8: burs at bar edges
L10: copper drag
R. Commutator bar wear
L. Commutator bar faults
PARTICULAR TYPES (CONTINUATION)
T14: Dark fringe due to low bar L4
T16: Dark fringes due to high mica L6
T18: Dark local patches due to burs L8
T16
L2 L4 L6
L10L8
T14 T18

29
29
Mersen’s services
For any technical expertise, maintenance or training, Mersen experts offer their extensive
knowledge, years of experience and global reach.
On-site practical support throughout the world
Commutation expertise
Measurements and diagnostics
Support service on a daily basis
Technical assistance by phone
Technical documentation on-line on our website: www.mersen.com or upon request
Mersen created the WindtrackerTM
Service in order to support wind farm operators.
WindtrackerTM
experts, dedicated wind engineers and technicians, bring you up tower
services, diagnostic capabilities, specific technical support and training, allowing you to
optimize your wind turbine performance. They are supported by a large network of special-
ists in five continents, allowing Mersen to respond to your needs, wherever the location.
Mersen provides training courses for maintenance of electric motors.
For over twenty five years, more than 3,000 technicians have been undergone training,
either at our facility (STAGELEC) or theirs (EXTELEC).
Diagnostics
In situ commutator, slip ring and brush-holder refurbishment:
• Surface re-conditioning
• Mica undercutting (commutators)
• Bar edge chamfering (commutators)
• Helical groove edge chamfering (slip rings)
• Out-of-round machining
• Carbon brush pressure measurement
• Proposal of suitable carbon brush grade
• Redesign of the complete carbon brush, brush-holder and commutator / slip ring system
• Installation of features to improve the performance of your machines (remote carbon
brush wear monitoring, dust extraction solutions...)
• Retrofit solutions
Support services on a daily basis
Mersen’s maintenance and service offerings
Expertise
WindtrackerTM
services
Training
Maintenance
Windtrac
kerTM servi
ces
06

30
30
TECHNICAL GUIDE - MERSEN’S SERVICES
Tools and accessories
Mersen offers tools and accessories for carbon brush use and electrical rotating machine
maintenance:
CL-Profiler:
• To measure commutator / slip ring profiles
• Low speed inductive probe
ComPro2000TM
• To measure commutator profiles during operation
• Any speed, non-contact eddy-current transducer
• Contact measurement
• Ruby tip for “live” measurements
Electronic force gauges for measuring brush-holder pressure systems
Tools for maintenance of electrical rotating machine surfaces:
• Grinding stones (abrasive cloth, brush seating stones)
• Scrapers and slotting files
Mica undercutters
Stroboscopes for slip ring, commutator and carbon brushes control
on rotating machines
Carbon brush wear indicator systems
Roughness meters
Complete toolkit for maintenance of slip rings and commutators (Please consult us)
• 0-2.5 daN force gauge for measuring spring pressure
• Battery-operated illuminated magnifier, for monitoring films and carbon brushes
• Thickness gauges (11 blades) for measuring carbon brush / brush-holder clearance
• 0-200 mm caliper for measuring carbon brush wear
• Insulated probe for assessing carbon brush vibrations
• Grinding stones
• Abrasive cloth

31
31
How to order carbon brushes?
A carbon brush is clearly defined by four characteristics:
The part number engraved on the brush or its grade (material and possible treatments)
Its shape and main dimensions (see on page 18)
Additional hardware type or attachment method (see on pages 19 to 21)
The application and motor characteristics
The part number is the best way to identify a brush, but any additional information will help.
There are also other ways to define a carbon brush:
DRAWING CATALOGUES
We can produce brush drawing catalogues containing the drawings and carbon brush
model references used in our customers’ plants. These catalogues make it easier for the
maintenance people to identify and order spare carbon brushes. Each carbon brush is
taken up by drawing and code number. To place an order you just have to quote the code
mentioned in the drawing catalogue.
IDENTIFICATION BY THE BRUSH-HOLDER
If it is a Mersen brush-holder, you just have to mention its type, the “t x a” cage dimensions,
and the carbon brush grade.
For modular brush-holders (MONG, MOSPI type), it is necessary to indicate the sheath
height (N, B, H ou TH), which determines the carbon brush height.
The shunt length, which depends on the brush gear arrangement on the motor, also has
to be mentioned, along with the terminal bolt diameter.
For all other types, we need a carbon brush sample or a brush-holder drawing, as well as
the motor type and characteristics.
CARBON BRUSH SAMPLE
A carbon brush sample, even worn out, will generally enable us to determine the main
dimensions except the brush height, which has to be selected from the list issued by the
I.E.C. according to the brush-holder, and given to us separately.
CARBON BRUSH DRAWING (OR SKETCH)
Excluding the requirements based on norms or Mersen manufacturing standards, there
are few additional specifications required to make a carbon brush drawing.
Except in very specific cases, there is no need to specify:
Tolerances on the main brush dimensions and on the shunt lengths
Chamfer dimensions
Type and thickness of materials used for attachments and connections
Cross section and composition of shunts
Shunt and terminal part fastening process
Insertion depth of the shunts into the brushes
Overall dimensions of the terminal parts
We can supply most of the carbon brushes fitting any motor type within one week, or even
one day under certain conditions.
Characteristics and identification
Delivery
07

32
32 Please fill this form out to help us find the most suitable carbon brush
for your specific application(s).
CARBON BRUSH
APPLICATION DESCRIPTION FORM
(Text conforms with IEC norm 60136)
Information concerning the machine:
1• Machine manufacturer: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2• Machine type: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3• Generator: CC CA – Motor: CC CA
Direction of rotation: Reversible yes no
4• Converter: CC - CA CA - CC
5• SPEED (rpm). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6• VOLTAGE (V). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7• CURRENT (Amps) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8• POWER (kW). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9• Duty: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10• Duty cycle (including no load %):
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11• Excitation : Shunt Separate Series Compound
12• Machine construction : Open Protected Closed
13• CARBON BRUSH MANUFACTURER AND GRADE . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14• The slip rings are located:
Between Outside the bearings
15• Are the slip rings in a closed enclosure? yes no
Machine’s environment:
16• Type of industry: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17• Ambient temperature (°C / °F): . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18• Temperature in service (°C / °F): . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19• Relative humidity (%): . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20• Oil vapor: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21• Corrosive gases - Type? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22• Dust – Nature: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23• Vibration? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating information:
24• Average brush life (hours): . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25• DESCRIPTION OF ANY PROBLEMS (if any)
Questions in blue are essential information for us to determine the best brush grade appropriate to your machine
Commutator Slip rings
DIAMETER:
Nr of bars: ….......…....….....…
Bar width: ….......…......….......…......……
Micas width:
NR OF TRACKS: ….......…....….....….....
NR OF BRUSHES
PER TRACK: ….......….....….......….....…....
NR OF POLES: ….......…....….....….......…
BRUSH DIMENSIONS:
(see Fig.1)
t =…….......... a = …….......... r = ….….........
BRUSH BOTTOM ANGLE
(see Fig.3, 4 and 5)
α =…….......…....….......... °
TOP BEVEL ANGLE (see Fig.10)
β =…….......…....….......... °
SPLIT BRUSH?
Fig 6 Fig 7
Fig 8 Fig 9
The brushes on the same
path are:
In line Staggered
DIAMETER:
Width: ….......…....….....….......…....….........
NUMBER: 2 3
MATERIAL: ….......…....….....…...........….
HELICAL GROOVE:
with without
NR OF BRUSHES
PER RING: ….......….....….......….....…......
BRUSH DIMENSIONS:
(see Fig.2)
t =…….......... a = …….......... r = ….….........
BRUSH BOTTOM ANGLE
(see Fig.3, 4 and 5)
α =…….......…....….......... °
TOP BEVEL ANGLE (see Fig.10)
β =…….......…....….......... °
Split brush?
Fig 6 Fig 7
Fig 8 Fig 9
CURRENT PER RING:
.…...........................…......................................A
CC CA
26• Commutator’s Slip ring’s condition
Good Glossy Matt
Smooth Worn out Grooved
Uniform Marked
Marks: Evenly distributed Unevenly distributed Burnt
Color: Light Average Dark
Nominal
In service
Normal Max.
Fig.1 Fig.3 Fig.4 Fig.5
Fig.2
Radial
α = 0
α α
Trailing
Commutator
Reaction
Slip rings
Fig.7 Fig.8Fig.6
Fig.9Fig.6 Single box Single finger
Split brush
Fig.7 Single box Two fingers
Split brush
Fig.8 Tandem boxes Two fingers
Tandem brushes
Fig.9 Tandem boxes Two fingers
One split brush in each box
a
a
r
r
t
t
Company . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Date. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Surname / Name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Phone Nr. . . . . . . . . . . . . . . . . Fax Nr . . . . . . . . . . . . . . . .
Email . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
APPENDICES

33
33
WHEN POSSIBLE PLEASE SEND US A SAMPLE OF THE CARBON BRUSH IN USE (even if worn)
or a detailed sketch of the brush with its shunt and terminal (Use sketch Fig. 10 below as a guide).
Essential information for the manufacture of a carbon brush
Dimensioned manual sketch of the brush in use
I Shunt length
in mm
Diameter or width
of ﬁxing gap in mm
Fixing gap width
or diameter in mm
If pressure clip
or insert required
l Shunt length
in mm
Shunt entry
α Bottom bevel
angle if present
β Top bevel angle
if present
Fig.10
a
l
t
r
w
APPENDICES

34
STANDARD SHAPES
34
APPENDICES
SHAPES OF NEW TERMINALS (recommended)
SHAPES OF OLD TERMINALS
Special shapes
of terminals

35
35
APPENDICES
Shape of the brush
Special
shapes Shape above with a “S” sufﬁx
The drawings represent 1 shape per box
For example
Brush Pair
2 boxes = 2 shapes
Split brush
1 box = 1 shapeBe careful: the number
of wafers is multiplied by 2
Length of the shunt
to the axis of the bolt
Commutator
Shapes in accordance with NEMA standard
(National Electrical Manufacturers Association) N° CB-1-1995
Top view
Slip ring
Shape of the terminal
and bolt diameter
SHUNT LOCATION
SANDWICH

36
QUESTIONNAIRE
FOR THE CHOICE OF A BRUSH-HOLDER PRESSURE SYSTEM
Identiﬁcation of the spring and spring carriers for European models
Indicate the letter corresponding to your need:
Dimensions and characteristics
Other information
A
D
H KJI
GFE
CB
If the spring you need is not shown above, please provide a sketch on the reverse side of the form, showing front and side views or
alternatively send us a sample. Minimum order quantity: 4 pieces.
Brush size
Spring
Spring carrier
Brush-holder
t: . . . . . . . . . . . . . . . . . . . mm
Diameter:. . . . . . . . . . . . . mm
Width: . . . . . . . . . . . . . . . mm
Material: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Carrier engraving: . . . . . . . . . . . . . . . . . . . . . . . .
a: . . . . . . . . . . . . . . . . . . . mm
Width: . . . . . . . . . . . . . . . mm
Height : . . . . . . . . . . . . . . mm
Length:. . . . . . . . . . . . . . . mm
Quantity: . . . . . . . . . . . . . . . .
r: . . . . . . . . . . . . . . . . . . . mm
Thickness: . . . . . . . . . . . . mm
Insulated:. . . . . . . . . . . . . . . .
Delivery with brushes
YES
NO
Width: . . . . . . . . . . . . . . mm
Dimension from bottom of holder to the mounting pin: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . mm
36
APPENDICES
Company . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Date. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Surname / Name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Phone Nr. . . . . . . . . . . . . . . . . Fax Nr . . . . . . . . . . . . . . . .
Email . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

37
Sketch for front and side views
Special request
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
.........................................................................................................................................................
37
APPENDICES

• Apparent density........................................................................................................14, 15
• Bakelite graphite or resin-bonded carbon brush (grade).......................................11, 15
• Bar edge chamfering ...................................................................................................3, 29
• Carbographitic (grade) ........................................................................................10, 14, 23
• Carbon brush bedding / seating .....................................................................................22
• Carbon brush guiding / Brush-holders ......................................................................4, 22
• Carbon brush position...............................................................................................18, 31
•• Carbon brush pressure ........................................................ 4, 5, 6, 13, 16, 22, 23, 29, 30
• Commutation, commuting.......................................................................3, 5, 6, 11, 26, 29
• Contact surface..................................................................................................6, 7, 19, 22
• Corrosive vapors or gases..........................................................................................7, 25
• Current density...........................................................................6, 9, 10, 11, 12, 13, 16, 17
• Current distribution ...................................................................................................4, 5, 6
• Dual grade (composite) carbon brush .......................................................................5, 20
• Dust .......................................................................................................................6, 7, 8, 29
• Electrographitic (grade).........................................................................................9, 14, 23
• Flexural strength........................................................................................................14, 15
• “μ” friction coefﬁcient / Friction ...............................................................................4, 6, 7
• Humidity................................................................................................................5, 6, 7, 25
• Impregnation ................................................................................................................9, 12
• Maximal load, underload, overload ..................................................................4, 6, 25, 27
• Metal content (grade).................................................................................................12, 15
• Metal-graphite carbon brush (grade) .................................................................12, 15, 23
• Mica, mica undercutting ........................................................................... 3, 23, 28, 29, 30
• Multi wafer carbon brush ............................................................................................5, 20
• Oils and hydrocarbons..........................................................................................7, 25, 27
• Out-of-round, run out, deformation........................................................... 3, 4, 23, 25, 29
• (Peripheral) speed................................................4, 5, 9, 10, 11, 12, 13, 14, 15, 16, 17, 23
• Resistivity ...............................................................................................................6, 14, 15
• Sandwich carbon brush ..........................................................................................5, 6, 20
• Shore hardness..........................................................................................................14, 15
• Skin, ﬁlm .......................................................................... 5, 6, 7, 22, 23, 24, 25, 26, 27, 30
• Soft graphite carbon brush (grade)....................................................................10, 15, 23
ring carbon brushes ..............................................................................................5
dition / Roughness ................................................................. 3, 4, 22, 23, 29
ensions...................................................................................................18
.........................................................................................5, 9, 11, 12, 13
tact drop ..............................................................................................5
.............................................................................................4, 5, 10, 30
Occurrence of technical terms
in this guide
• Staggering
• Surface conditi
• “t”, “a”, “r” dime
• Temperature..........
• Voltage drop / Cont
• Vibration.................

AE-TDS/01 Functions of a good carbon brush, what
you should know
AE-TDS/02 Condition of the surface of commutators
and slip rings - Roughness
AE-TDS/03 Chamfering of commutator bar edges
Machining of ring helical grooves
AE-TDS/04 Brush and brush-holder tolerances on “t”
and “a” dimensions
AE-TDS/05 Losses in carbon brushes
AE-TDS/06 Setting the neutral at rest
AE-TDS/07 Sandwich brushes – Composite brushes
AE-TDS/08 Preventive maintenance
AE-TDS/09 Circumferential brush stagger
AE-TDS/10 Threading on slip rings
AE-TDS/11 Brush spring pressure
AE-TDS/12 Ventilation
AE-TDS/13 Aspects of commutator / slip ring skins
AE-TDS/14 Brush sparking
AE-TDS/15 Brush wear
AE-TDS/16 Standardization of carbon brush dimensions
AE-TDS/17 Air humidity
AE-TDS/18 Degreasing of commutators and rings
AE-TDS/19 Brush seating
AE-TDS/20 Slip ring brushes
AE-TDS/21 Copper bridging of commutator bars
(copper dragging)
AE-TDS/22 Ghost marking on synchronous machines
slip rings (ghosting)
AE-TDS/23 Silicones
AE-TDS/24 Dust arising from brush wear
AE-TDS/25 Underloaded machines
In addition to present Technical Guide, other documents can be supplied upon request.
Do not hesitate to contact us.
LIST OF MERSEN’S TECHNICAL DATA SHEETS (also available from www.mersen.com):
Mersen is a global Expert in materials and solutions for extreme environments as well as in the safety
and reliability of electrical equipment.
Our markets:
Energy: • Wind • Hydro • Photovoltaic • Nuclear Power • Conventional Thermal Power • Oil & Gas
Transportation: • Railways • Aerospace & Aeronautics • Ports & Marine • Electrical Vehicles
Electronics: •Polysilicon •Power Electronics •Semiconductors •Compound Semiconductors •Optical Fiber Production
Chemicals & Pharmaceuticals: • Organic Chemicals • Inorganic Chemicals • Fine Chemicals & Pharmaceuticals
Process industries: • Metallurgy • Mining • Oil & Gas • Cement • Pulp & Paper • Rubber & Plastic
• Water & Wastewater Treatment • Assembly Manufacturing • Mould Industry • Glass Industry • Sintering
• Furnace Industry
Other Markets: • Commercial • Residential • Data Communication • Elevators • Forklifts

www.mersen.com
A GLOBAL PLAYER
Global expert in materials and solutions for
extreme environments as well as in the safety and
reliability of electrical equipment, Mersen designs
innovative solutions to address its clients’ speciﬁc
needs to enable them to optimize their
manufacturing process in sectors such as energy,
transportation, electronics, chemical, pharmaceutical
and process industries.
AE-Tech/CBGB-1208
Photos:©MersenImageLibrary-Fotolia:VasilyevDmitry.

Carbon Brushes Technical Guide

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