EET402 -M3-Ktunotes.in.pdf NOTES ON ESD.
- 2. Module 3 Domestic Installation (10 hours) General aspects as per NEC and IS 732 related to the design of domestic dwellings availing single phase supply (LV) and three phase supply (MV) for a connected load less than 15kW. Load Survey- common power ratings of domestic gadgets- connected load-diversity factor selection of number of sub circuits (lighting and power)-selection of MCB distribution boards to provide over load, short circuit and earth leakage protection. Principle of operation of MCB, MCB Isolator, ELCB/RCCB and RCBO. Selection of CBs for protection and grading between major and minor sections. Selection of wiring cables, conduits as per NEC and IS 732 Design of electrical schematic and physical layout drawings for low and medium class domestic installation. Preparation of schedule of works and bill of quantities (cost estimation excluded). Pre-commissioning tests- Insulation resistance measurement, continuity test, polarity test, and earth resistance measurement as applicable to domestic installations. Downloaded from Ktunotes.in
- 3. •Domestic dwellings Residential or domestic dwellings are those buildings intended for normal residential purpose. The primary considerations in planning the electrical layout in domestic dwellings are economy and safety. Besides these, other considerations such as efficiency and reliability, convenience and provisions for future expansion are also valid. These buildings are classified into •One or two family dwellings or Stand alone building (occupied by members of single family not more than 20 persons) •Apartment buildings/flats (3 or more families) Downloaded from Ktunotes.in
- 4. Electrical system design of domestic buildings Objective • Safety and economy •Energy efficiency •Reliability • Convenience •Provision for expansion •Estimation of load requirements Downloaded from Ktunotes.in
- 8. Calculation of total connected load •When all the light, fan and socket points are decided, total connected load is calculated. •Total kVA is the sum of kVA of all individual loads. Maximum demand kVA is not equal to installed kVA. •To find the maximum kVA demand of the building two factors are useful: • Factor of maximum utilisation ku • Factor of simultaneity ks . Downloaded from Ktunotes.in
- 9. Utilisation factor (Ku) Normally power consumed by load is less than the normal rating of the load. So utilisation factor Ku is used to calculate the estimate of load. Std values of Ku are •For fluorescent lighting Ku=1 •For water heaters Ku=1 •For industrial loads(motor) Ku=0.75 •For socket outlets Ku=depends on type of apparatus. Downloaded from Ktunotes.in
- 10. Factor of simultaneity (ks) •All loads will not be operated simultaneously. So this factor is taken into account for the purpose of estimating. Simultaneity factor is the reciprocal of diversity factor. •For domestic installation, diversity factor is taken as 2 to 2.5. Downloaded from Ktunotes.in
- 11. Supply Voltage Max. connected load kW/kVA Max. contract demand kVA 240V,1 phase 5kW 415,3 phase 100kVA 11kV 3000 22/33 kV 8000 66kV 8000 Relation between connected load and type of supply Downloaded from Ktunotes.in
- 12. Height of batten 2.5m above floor level Height of switch board 1.3m above floor level Height of distribution board 1.5m above floor level Height of brackets for light points 2.5m above floor level Assumptions made in estimation Downloaded from Ktunotes.in
- 13. General requirements of electrical installation •All electrical installation should be carried out according to India Electricity Act and regulations of concerned electric supply authority. •Following steps should be adopted for estimation of electrical installation. 1) Layout wiring •Power and heating subcircuit should be separate and distinct from lighting and fan subcircuit. Downloaded from Ktunotes.in
- 14. Circuit and Subcircuit • Electrical apparatus are connected to supply main and to the associated protective and controlling devices. This arrangement of cables is known as circuit. • A circuit that feeds apparatus directly is known as a subcircuit. From the distribution board the supply can be directly taken to the loads as shown in the fig. • In the above connection if there is a short circuit in any part of the wiring the fuse will disconnect the supply to the whole installation. Also If the number of load points is large ,the voltage available at the farthest end will be low due to the voltage drop in the line. So avoid this situation the wiring is divided into smaller circuits called subcircuit. Downloaded from Ktunotes.in
- 15. •Subcircuits are divided into two groups •Light and fan subcircuit:- This subcircuit includes fan ,light and 5A socket outlet points. Maximum points should not exceed ten. The load on each subcircuit shall not exceed 800 watts. •Power sub-circuit:-Maximum point should not exceed two. The load is restricted to 3000 watts. Downloaded from Ktunotes.in
- 16. 2) Conductors • All conductors should be of copper or aluminium. • The conductors for final subcircuit wiring should have a nominal cross sectional area not less than 1 mm2 for copper and 1.5 mm2 if aluminium is used . • For power wiring minimum cross sectional area is 1.5 mm2 for copper 2.5mm2 for aluminium . Downloaded from Ktunotes.in
- 17. 3) Rating of fan ,lamp and socket outlet points. 4) Type of connection Select either looping-in or joint box type connection. Normally looping –in system connection is preferred. Downloaded from Ktunotes.in
- 18. 5) Single phase supply •All loads are connected in parallel and supplied at same potential. Downloaded from Ktunotes.in
- 19. 6) Three phase supply Downloaded from Ktunotes.in
- 20. Diversity factor Downloaded from Ktunotes.in
- 21. Device Full Form Purpose MCB Miniature Circuit Breaker Over current/Short circuit protection MCCB Molded Case Circuit Breaker Over current/Short circuit protection ELCB Earth Leakage Circuit Breaker Earth leakage protection RCCB Residual Current Circuit Breaker Earth leakage protection RCD Residual Current Device Earth leakage protection RCBO Residual-Current circuit Breaker with Overcurrent protection Earth leakage protection + Over current protection + Short circuit Protective devices used in domestic installations Downloaded from Ktunotes.in
- 22. Miniature Circuit Breaker (MCB) A miniature circuit breaker (MCB) automatically switches off electrical circuit during an abnormal condition of the network such as overload and faulty condition. Nowadays MCB are used in low voltage electrical network instead of a fuse. Comparison of fuse and MCB • The fuse may not sense it but the miniature circuit breaker does it in a more reliable way. • MCB is much more sensitive to overcurrent than fuse. • Handling an MCB is electrically safer than a fuse. • Quick restoration of supply is possible in case of a fuse as because fuses must be re-wirable or replaced for restoring the supply. Restoration is easily possible by just switching it ON. Downloaded from Ktunotes.in
- 23. MCB working • Under normal working conditions, MCB operates as a switch (manual one) to make the circuit ON or OFF. • Under overload or short circuit condition, it automatically operates or trips so that current interruption takes place in the load circuit. • The visual indication of this trip can be observed by automatic movement of the operating knob to OFF position. • This automatic operation of MCB can be obtained in two ways; they are magnetic tripping and thermal tripping. • Under overload condition, the current through the bimetal causes to raise the temperature of it. This causes the deflection of bimetal Downloaded from Ktunotes.in
- 24. • This deflection releases the trip latch and hence contacts get separated by thermal tripping. • Under short circuit or heavy overload conditions, magnetic tripping occurs. • Under normal working condition, the moving contact is held in a position by light spring because magnetic field generated by the coil is not sufficient to attract the latch. • When a fault current flows, the magnetic field generated by the coil is sufficient to overcome the spring force. • So the moving contact moves and then actuate the tripping mechanism. • In both magnetic and thermal tripping operations, an arc is formed when the contacts start separating. This arc is then forced into arc splitter plates via arc runner. • These arc splitter plates are also called arc chutes where arc is formed into a series of arcs and at the same time energy extracted and cools it. Hence this arrangement achieves the arc extinction. Downloaded from Ktunotes.in
- 27. Miniature Circuit Breakers have the following Specifications • Current rating Amperes (A) • Short Circuit Rating Kilo Amperes (kA) • Operating Characteristics B, C , D Curves etc. Miniature Circuit Breakers are usually available in the range of 0.5 A to 100 A. An MCB's Short circuit rating is given in Kiloamps (3-10 kA and this indicates the level of its ability to work). For example a domestic MCB would normally have a 6 kA fault level, whereas one used in an industrial application may need a unit with a 10 kA fault capability. Downloaded from Ktunotes.in
- 28. MCBs are classified according to tripping over range of fault current as follows: 1.Type B MCB 2.Type C MCB 3.Type D MCB 4. Type K MCB 5. Type Z MCB Downloaded from Ktunotes.in
- 29. •Type B MCB This type of MCB trips between 3 and 5 times full load current. Type B devices are mainly used in residential applications or light commercial applications. The surge current levels in such cases are relatively low. •Type C MCB This type of MCB trips between 5 and 10 times full load current. This is used in commercial or industrial type of applications .The connected loads are mainly inductive in nature (e.g. induction motors). Downloaded from Ktunotes.in
- 30. •Type D MCB This type of MCB trips between 10 and 20 times full load current. These MCBs are use in specialty industrial / commercial uses where current inrush can be very high. Examples include transformers or X-ray machines, large winding motors etc. •Type K MCB MCB with class K trip characteristics trips instantaneously when the current flowing through it reaches between 8 to 12 times the rated current. Suitable for inductive and motor loads with high inrush currents. Downloaded from Ktunotes.in
- 31. •Type Z MCB MCB with class Z trip characteristics trips instantaneously when the current flowing through it reaches between 2 to 3 times the rated current. These type of MCBs are highly sensitive to short circuit and are used for the protection of highly sensitive devices such as semiconductor devices. Downloaded from Ktunotes.in
- 33. Type Tripping Current Operating Time Type B 3 To 5 time full load current 0.04 To 13 Sec Type C 5 To 10 times full load current 0.04 To 5 Sec Type D 10 To 20 times full load current 0.04 To 3 Sec Type K 8 To 12 times full load current <0.1 Sec Type Z 2 To 3 times full load current <0.1 Sec Downloaded from Ktunotes.in
- 34. •Types of MCBs based on poles No. of Pole for MCB depends on Single Phase & Three Phase Power •Single Pole (SP) MCB •A single pole MCB provides switching and protection for one single phase of a circuit. Used for Single Phase circuit Downloaded from Ktunotes.in
- 35. •Double Pole (DP) MCB A two Pole MCB provides switching and protection both for a phase and the neutral. Used for Single Phase circuit •Triple Pole (TP) MCB A triple/three phase MCB provides switching and protection only to three phases of the circuit and not to the neutral. Used for Three Phase circuit. Downloaded from Ktunotes.in
- 36. • 3 Pole with Neutral (TPN (3P+N) MCB) A TPN MCB, has switching and protection to all three phases of circuit additionally Neutral is also part of the MCB as a separate pole. However , Neutral pole is without any protection and can only be switched. Used for Three Phase circuit with Neutral. • 4 Pole (4P) MCB A 4 pole MCB is similar to TPN but additionally it also has protective release for the neutral pole. This MCB should be used in cases where there is possibility of high neutral current flow through the circuit as in cases of an unbalanced circuit. • Used for Three Phase circuit with Neutral. Downloaded from Ktunotes.in
- 37. MCCB-Molded Case Circuit Breaker • The main distinction between molded case and miniature circuit breaker are that the MCCB can have current ratings of upto 2,500 amperes, and its trip settings are normally adjustable. • The MCCB provides protection against overload, short circuit faults and is also used for switching the circuits. • The wide current ratings and high breaking capacity in MCCB find their use in industrial applications. MCCB can be used for protection of capacitor bank, generator protection and main electric feeder distribution. • The Frame, also known as the molded case, provides an insulated housing to mount all of the circuit breaker components. This will often be made of a glass-polyester material or thermoset composite resin that combines ruggedness and high dielectric strength in a compact design. Downloaded from Ktunotes.in
- 38. •Main difference between MCB & MCCB Sl. No MCB MCCB 1 It stands for Miniature Circuit Breaker. It stands for Molded Case Circuit Breaker. 2 Rated current not more than 125 Ampere. Rated Current up to 1600A 3 Its interrupting current rating is under 10KA Their interrupting current ranges from around 10KA -85KA 4 MCB is mainly used for low Breaking capacity requirement mainly domestic. MCCB is mainly used for both low and high Breaking capacity requirements mainly industrial. 5 Its trip characteristics are normally not adjustable since they basically cater to low circuits. Its trip current may be fixed as well as adjustable for overload and magnetic setting. Downloaded from Ktunotes.in
- 39. •ELCB -Earth Leakage Circuit Breaker •ELCB, an acronym for Earth Leakage Circuit Breaker detects directly the current leaking to the earth from a load device or installation. •The main purpose of the device is to prevent damages and injuries due to electric shocks. 2 types : •Voltage operated ELCB •Current operated ELCB (RCCB / RCD) Downloaded from Ktunotes.in
- 40. Voltage operated ELCB • Voltage Operate ELCB contains a relay coil or ELCB coil. One end of the ELCB coil is given connection to the body of the metal part and the other end to the earth wire. When the voltage of the load rises, there will be a difference in voltage between the load and the earth wire resulting in electric shock. This potential or voltage difference causes a current to flow from the load to the ground through the relay coil loop. When the voltage difference becomes greater than 50 volt, current through the loop moves the relay and hence disconnect the supply. • Voltage ELCBs are not recommended over current ELCB (RCCB) and no longer available because of old technology. Downloaded from Ktunotes.in
- 41. Current operated ELCB (RCCB / RCD) • The circuit consists a phase coil, neutral coil, search coil wound around the core of a transformer. • In normal conditions, same electric current flows through the phase and neutral. the neutral and phase coils are wound in a way such that an opposing magnetic flux is produced. • Since the current passing is same through the phase and neutral at normal conditions, their net magnetic effect and flux cancels out each other. Downloaded from Ktunotes.in
- 42. • When there is an earth fault, the current flowing through the phase and neutral will be different. In this case, magnetic flux in the core is not balanced, i.e., the sum of magnetic flux of phase and neutral coil is not zero. • Net remaining flux is called as Residual Flux. The residual flux changing periodically within the core of the transformer crosses the path of the search coil and produces an alternating voltage. This voltage will produce the current essential to trip the circuit breaker. Downloaded from Ktunotes.in
- 43. RCBO( Residual Circuit Breaker with Overload) • RCDs or RCCB detect an imbalance in the live and neutral currents. A current overload, however large, cannot be detected. RCDs don’t offer protection against current overloads. • It is now possible to get an MCB and RCD in a single unit, called an RCBO.RCBOs are commonly used in applications where there is the need to combine protection against overcurrent (overload and short-circuit) and protection against earth leakage currents. They can generally be fitted into a Consumer Unit in place of an MCB. They tend to be quite expensive. Downloaded from Ktunotes.in
- 44. Cross Section of Conductors The cross section of conductors shall be determined according to: •their admissible maximum temperature •the admissible voltage drop •the electromechanical stresses likely to occur due to short circuits • the maximum impedance with respect to the functioning of the short-circuit protection. Downloaded from Ktunotes.in
- 45. Type of Wiring and methods of Installation The choice of the type of wiring and the methods of installation depend on: a) the nature of the locations b) the nature of the walls or other parts of the building supporting the wiring c) accessibility of wiring to persons and live; stock d) Voltage e) the electromechanical stresses likely to occur due to short circuits, and f) other stresses to which the wiring may be exposed during the erection of the electrical installation or in service. Downloaded from Ktunotes.in
- 47. •A typical range of single phase RCBO – 6A, 10A, 16A, 20A, 25A, 32A, 40A, 63A. •A typical range of Three phase RCBO – 16A, 25A, 32A, 40A, 63A. Downloaded from Ktunotes.in
- 49. A three occupant building has to be electrified independently from a common energy meter. Design the distribution boards with accessories for each resident having 10nos of light circuits, 6 no.s of power circuits. Downloaded from Ktunotes.in
- 50. •Load for each residents •Total circuits = 10 nos = 10*800watts/circuit = 8000 watts •Total no. of power circuits = 6 nos. = 6*3000 watts/circuit = 18000 watts •Total load estimated as per given number of circuits = 26kWatts. •Select 3 phase supply •Accessories required per resident Incoming: Outgoing: Downloaded from Ktunotes.in
- 51. Fig. shows the plan of a small flat. The position of light and fan points and switch board have been shown. a) Decide the no.of subcircuits and show these in the installation plan. b) Calculate the size and length of the wire required for wiring. c) Estimate the quantity of material. Downloaded from Ktunotes.in
- 56. Design an electrical schematic for the residential building with following details. Locate the positions of meter board, Main Switch board, DB, switch boards. Downloaded from Ktunotes.in
- 57. A single storied residential building with two bedrooms with attached toilets, one dining room, one living room, kitchen, and sit out. Decide the required number of light points, fan points, 5A socket outlet, 15A socket outlet. Decide the number of sub circuits required. Determine the connected load, type of supply required, sub circuits required, maximum demand. Downloaded from Ktunotes.in
- 58. •The plan layout of a two bed room domestic building is shown in figure. Locate the light, fan, socket points etc., required for the electrification of the building as per NEC requirements. Calculate (a) Connected load of the building (b) Maximum demand in kW (c) Type of supply required (d) Number of light and power circuits (e) Details of the distribution board Downloaded from Ktunotes.in
- 59. A rest house has four air-conditioned bed rooms with attached toilets, dining hall and kitchen. Prepare the room wise list of electrical materials for the installation. Draw the schematic diagram showing the ratings of MCBs and sub circuits. Design is based on the NEC guide lines. Assume all required data. Downloaded from Ktunotes.in
- 60. Precommissioning Test • It is a necessary prerequisites under statutory provisions. This is done in accordance with IS-732. It ensures • that the installations satisfies all the safety regulations. • Good material and workmanship have gone into the work • Installation is good in working condition • Faults if any in the installation are located and remedial measures are suggested before energising. Precommissioning test includes:- • Visual Inspection:-This is necessary to verify the installation is In compliance with Indian standard specifications Correctly erected in accordance with the relevant code No visual damage is seen outside. Downloaded from Ktunotes.in
- 61. Testing :- testing is done in the following sequence 1. Continuity of the final circuit conductors. :- It is carried out in all final circuits to make sure that there is no discontinuity in the circuit. The most common and basic way of performing a continuity test is with the help of a multimeter. Connect one lead to phase wire and other to neutral wire. The device will give a beep when there is continuity. 2. Continuity of protective conductors All protective conductors should be tested separately to make sure that they are electrically sound and are correctly connected. Downloaded from Ktunotes.in
- 62. 3. Insulation resistance It is measured between the live conductors and earth and between live conductors. For larger installation this is done by dividing the installation into smaller units, each containing not less than 50 outlets. The test voltage applied for insulation measurement is For voltages upto 250V 500 V 250 to 500 V 1000V Above 500 V 2500V Downloaded from Ktunotes.in
- 63. The following steps are involved in the measurement of insulation between live conductors and earth. • Main switch is in OFF position. •All fuses, MCBs are ON • All lamps and other accessories are in place. •Phase and neutral conductor are connected together near the main switch. •The insulation resistance between conductor and earth is measured using a megohm meter of appropriate voltage class. • Measured value shall not be less than 1 Megaohm. Downloaded from Ktunotes.in
- 64. The following steps are involved in the measurement of insulation resistance between conductors Steps involved are 1) The main switch is placed in the OFF position 2) The phase and neutral conductors are not connected together. 3) All switches are placed in the ON position. 4) All lamps and accessories are removed. 5) All fuses/MCBs beyond the main switch on the consumer side are ON. 6) The insulation resistance between any two phases are recorded using a megaohm meter. Measured value shall not be less than 1 Megaohm. Downloaded from Ktunotes.in
- 65. 3. Polarity Test This test will verify that all the switches installed in the system are connected in current carrying conductor and not in neutral. Steps involved in Polarity Test are • All equipment are disconnected. •All switch covers are open. •Use a test lamp with long leads. •Touch one end of the lead to the neutral point. • Touch the other lead to the input terminal of the switch. If the lamp burns ,the polarity is correct. Downloaded from Ktunotes.in
- 66. 4. Earth electrode resistance test •Earth electrode–It is the conductive part which may be embedded in the soil. • Earth electrode resistance–It is the resistance of an earth electrode to Earth. •The purpose of this test is to establish that the resistance of the soil surrounding an earth electrode is suitable and that the electrode makes contact with the soil. •Two auxiliary earth electrodes, besides the test electrode, are placed at suitable distance from the test earth electrode (see Fig). A measured current is passed between the earth electrode to be tested and an auxiliary current electrode ‘C’, and the potential difference between the electrode earth electrodec and auxiliary electrode ‘P’ is measured. Measured voltage and current values are used to calculate the electrode resistance. Downloaded from Ktunotes.in