PLT 302 ELECTRICAL INSTALLATION I Chapter 2 Final

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PLT 302 : ELECTRICAL INSTALLATION I Chapter 2: Final Circuit & Load Estimation

PLT 302 : ELECTRICAL INSTALLATION I Chapter 2: Final Circuit & Load Estimation

2. 1 Definition of Final Circuit A circuit connected directly to current using equipment,

2. 1 Definition of Final Circuit A circuit connected directly to current using equipment, or to a socket outlet or other points for connection of such equipment. An outlet is defined as the termination of fixed wiring feeding a luminaire, socket, or any current consuming appliance. From this it will be seen that a final circuit might consist of a pair of 1. 5 mm 2 cables feeding a few lights or a very 3 core cable feeding a large motor direct from a circuit breaker or main switchboard 2. 1. 1 Socket Outlet A device, provided with female contact which is intended to be installed with the fixed wiring, and intended to a receive plug. A luminaire track system is not regarded as a socket outlet system Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 2

2. 1 Definition of Final Circuit Figure 2. 1 : Schematic diagram of final

2. 1 Definition of Final Circuit Figure 2. 1 : Schematic diagram of final circuit Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 3

2. 2 Final Circuit Distribution Final circuit can be divided into the following types,

2. 2 Final Circuit Distribution Final circuit can be divided into the following types, all of which will need different treatment when planning the size of the conductors and the rating of the overcurrent devices. The general of final circuit are: 1. Final circuit feeding 13 A sockets to BS 1363 2. Final circuit feeding sockets to BS EN 60309 -2 (industrial type 16 A, 32 A, 63 A and 125 A) 3. Final circuit lighting 4. Final circuit motors 5. Final circuit cookers Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 4

2. 2. 1 Final Circuit Feeding 13 A sockets to BS 1363 The main

2. 2. 1 Final Circuit Feeding 13 A sockets to BS 1363 The main advantages of the 13 A socket with fused plug are that any appliance with a loading not exceeding 2. 99 k. W (13 A at 230 V) may be connected with perfect safety to any 13 A socket, and under certain conditions an unlimited number of socket may be connected to any one circuit. 13 A socket outlets circuits can be fed by; i. Radial circuits ii. Ring circuit Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 5

con’t Radial circuit arrangement Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 6

con’t Radial circuit arrangement Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 6

con’t Ring circuit arrangement A ring circuits utilises one additional conductor to loop back

con’t Ring circuit arrangement A ring circuits utilises one additional conductor to loop back to the sending end. Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 7

con’t IEE Standard Regulations for 13 A sockets These permit 13 A sockets to

con’t IEE Standard Regulations for 13 A sockets These permit 13 A sockets to be wired on the final circuits as follows (subject to any derating factors for ambient temperature, grouping or voltage drop): RADIAL CIRCUIT An unlimited number of socket outlets connected to a final circuit serving in floor area not exceeding 75 m 2 with 4 mm 2 PVC insulated cables on a radial circuit and protected by an overcurrent device of 30 A or 32 A rating. An unlimited number of sockets connected to a final circuit serving a floor area not exceeding 50 m 2 with 2. 5 mm 2 PVC insulated cables on a radial circuit and protected by an overcurrent device not exceeding 20 A. Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 8

con’t RING CIRCUIT An unlimited number of socket outlets connected to a final circuit

con’t RING CIRCUIT An unlimited number of socket outlets connected to a final circuit serving a floor area not exceeding 100 m 2 wired with 2. 5 mm 2 PVC insulated cables in the form of a ring, and protected by 30 A or 32 A overcurrent protective device. In actual practice, 10 number of socket outlets connected to a final circuit wired with 2. 5 mm 2 PVC insulated cables in the form of a ring. Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 9

2. 2. 1. 1 SPUR A spur is a branch cable connected to a

2. 2. 1. 1 SPUR A spur is a branch cable connected to a 13 A circuit. There are two type of spur in the market which are: i. Non fused spur ii. Fused spur Non Fused Spur The total number of non fused which may be connected to a 13 A circuit must not exceed the total number of sockets connected direct the circuit. Not more than one single or one twin socket outlet or one fixed appliance may be connected to any one spur. Non fused spurs may be looped from the terminals of the nearest sockets, or by means of a joint box in the circuit. The size of the cable feeding non fused spurs must be the same size as the circuit cable. Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 10

Con’t Fused Spur The cable forming a fused spur must be connected to the

Con’t Fused Spur The cable forming a fused spur must be connected to the ring circuit by means of fused connection unit or spurbox. The rating of the fuse in this unit shall not exceed the rating of the cable forming the spur and must not exceed 13 A Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 11

Malaysia Practice for 13 A Socket Outlet BS 1363 Types of 13 A Socket

Malaysia Practice for 13 A Socket Outlet BS 1363 Types of 13 A Socket Outlets Area 1. Single socket outlet 2. Malaysia Practices Size of wires Fuse/Circuit Breaker Rating 20 m 2 • 2. 5 mm 2 PVC cables 16 A Double socket outlet 20 m 2 • 2. 5 mm 2 PVC cables 20 A 3. Ring (10 Nos 13 A socket outlet provided they are all located within an area of not more than 1000 sq feet) 100 m 2 • 2. 5 mm 2 PVC cables 32 A 4. Radial (Max 6 Socket Outlets) 50 m 2 • 4 mm 2 cables 32 A PVC Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 12

2. 2. 2 Final circuit feeding sockets to BS EN 60309 -2 These socket

2. 2. 2 Final circuit feeding sockets to BS EN 60309 -2 These socket outlets are of the heavy industrial type, and are suitable for single or three phase with a scraping earth. Fuses are not fitted in the sockets or the plugs. Current ratings range from 16 A to 125 A (16 A, 32 A, 63 A & 125 A). The 16 A sockets whether single or three phase, may be wired only on radial circuits. The number of sockets connected to a circuit is unlimited, but the protective overcurrent device must not exceed 20 A. It is obvious that if these 16 A sockets are likely to be fully loaded then only one should be connected to any one circuit. The higher ratings will of course each be wired on a separate circuit. Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 13

2. 2. 3 Final circuit lighting Electric discharge lighting are divided into two groups:

2. 2. 3 Final circuit lighting Electric discharge lighting are divided into two groups: i. Operate in the 200 V/250 V range ii. High voltage type which may use voltage up to 5000 V to earth. The first group includes tubular fluorescent lamps which are available in rating 8 W to 125 W, sodium lamps which are rated from 35 W to 400 W, also high pressure mercury vapour lamps rated from 80 W to 1000 W, and other forms of discharge lighting. The second group includes neon signs and similar means of high voltage lighting. Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 14

2. 2. 3 Final circuit lighting Low voltage discharge lighting circuits: Regulations governing the

2. 2. 3 Final circuit lighting Low voltage discharge lighting circuits: Regulations governing the design of final circuits for this group are the same as those which apply to final circuits feeding tungsten lighting points. The current rating is based upon the ‘total steady current’ which includes the lamp, and any associated control gear, such as chokes or transformers, and also their harmonic currents. In absence of manufacturers’ data, this can be arrived at by multiplying the rated lamp power in watts by 1. 8, and is based on the assumption that the power factor is not less than 0. 85 lagging. Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 15

2. 2. 3 Final circuit lighting For low voltage discharge lighting: Based on assumption

2. 2. 3 Final circuit lighting For low voltage discharge lighting: Based on assumption that: The power factor, cos θ not less than 0. 85 lagging Total steady current which includes the lamp and any associated control gear such as chokes or transformers and their harmonic current For some fluorescent lamp circuit (especially the 125 W switch start type) Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 16

2. 2. 3 Final circuit lighting Circuit switches: Circuit switches controlling fluorescent circuits should

2. 2. 3 Final circuit lighting Circuit switches: Circuit switches controlling fluorescent circuits should be designed for purpose otherwise they should be rated at twice that of the design current in the circuit; quick-make and slow break switches must be used. Quick break switches must not be sued as they might break the circuit at the peak of its frequency wave, and cause a very high induced voltage might flash over to earth. Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 17

2. 2. 4 Final circuit motor Final circuit for motors need special consideration, although

2. 2. 4 Final circuit motor Final circuit for motors need special consideration, although in many respects they are governed by the regulations which apply to other types of final circuits. The current rating cables in a circuit feeding a motor must be based upon the full load current of the motors, although the effect of the starting current will need to be considered if frequent starting is anticipated. IEE Regulation 552 -1 -1 states all equipment, including cable, of every circuit carrying the starting, accelerating and load current of a motor shall be suitable for current at least equal to the full load current of the motor when rated in accordance with appropriate British Standard. Where the motor is intended for intermittent duty and for frequent starting and stopping, account shall be taken of any cumulative effects of the starting or braking current upon the temperature rise of the equipment of the circuit. Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 18

2. 2. 4 Final circuit motor Need for isolator • Every electric motor exceeding

2. 2. 4 Final circuit motor Need for isolator • Every electric motor exceeding 0. 37 k. W shall be provided with control equipment incorporating protection against overload of the motor. Several motors not exceeding 0. 37 k. W each can be supplied by one circuit, providing protection is provided at each motor. • All isolators must be ‘suitably placed’ which means they must be near the starter, but if the motor is remote and out of sight of the starter then an additional isolator must be provided near the motor. All isolators, of whatever kind, should be labelled to indicate which motor they control. • The cutting off of voltage does not include the neutral ins systems where the neutral is connected to earth. For the purposes of mechanical maintenance, isolators enable the person carrying out maintenance to ensure that all voltage is cut off from the machine and the control gear being worked upon, and to be certain that it is not possible for someone else to switch it on again inadvertently. Where isolators are located remote from the machine, they should have removable or lockable handles to prevent this occurrence. Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 19

2. 2. 4 Final circuit motor Motor starters • It is necessary that each

2. 2. 4 Final circuit motor Motor starters • It is necessary that each motor be provided with a means of starting and stopping, and so placed as to be easily worked by the person in charged of the motor. • The starter controlling every motor must incorporate means of ensuring that in the event of a drop in voltage or failure of supply, the motor does not start automatically on the restoration of supply, where unexpected re-starting could cause danger. Starters should be fitted with undervoltage trips, which have to be manually reset after having tripped. • Every motor having a rating exceeding 0. 37 k. W (1/2 hp) must also be controlled by a starter which incorporates an overcurrent device with a suitable time lag to look after starting current (IEE Regulation 552 -1 -2). • These starters are generally fitted with thermal overloads which have an inherent time lag, or with the magnetic type usually have oil dashpot time lags. These time lags can usually be adjusted, and are normally set to operate at 10% above full load current. Electronic protective relays are also available now and these provide a fine degree of protection. Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 20

2. 2. 4 Final circuit motor Rating of protective device IEE Regulation 433 -2

2. 2. 4 Final circuit motor Rating of protective device IEE Regulation 433 -2 -2 states that the overcurrent protective device may be placed along the run of the conductors (providing no branch circuits are installed), therefore the overcurrent protective device could be the one incorporated in the starter, and need not be duplicated at the commencement of the circuit. • Short circuit protection must be provided to protect the circuit, and shall be placed where a reduction occurs in the value of the current carrying capacity of the conductors of the installation (i. e such as in a distribution board). The device may, however, be placed on the load side of a circuit providing the conductors between the point where the value of current carrying capacity is reduced and the position of the protective device do not exceed 3 m length and providing the risk of fault current, fire and danger to persons is reduced to a minimum (IEE Regulation 433 -2 -2). Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 21

2. 2. 4 Final circuit motor • When motors take very heavy and prolonged

2. 2. 4 Final circuit motor • When motors take very heavy and prolonged starting currents it may well be that fuses will not be sufficient to handle the starting current of the motor, and it may be necessary to install an overcurrent device with the necessary time delay characteristic, or to install larger cables. • With three phase motors, if fuses protecting the circuit are not large enough to carry the starting current for a sufficient time, it is possible that one may operate, thus causing the motor to run on two phases. This could cause serious damage to the motor, although most motor starters have inherent safeguards against this occurrence. • The ideal arrangement is to back up the overcurrent device in the motor starter with HBC fuselinks which have discriminating characteristics which will carry heavy starting currents for longer periods than the overload device. If there is a short circuit, the HBC fuses will operate and clear the short circuit before the short circuit k. VA reaches dangerous proportions. Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 22

2. 2. 5 Final circuit cookers A cooker is regarded as a piece of

2. 2. 5 Final circuit cookers A cooker is regarded as a piece of fixed equipment unless it is a small table-mounted type fed from a plug by a flexible cord. Such equipment must be under the control of a local switch, usually in the form of a cooker control unit. This switch may control two cookers, provided both are within 2 m of it. In many cases this control unit incorporates a socket outlet, although often such a socket is not in the safest position for use to supply portable appliances, whose flexible cords may be burned by the hotplates. It is often considered safer to control the cooker with a switch and to provide a separate socket circuit. The protective device is often the most highly rated in a installation, particularly in a domestic situation, so there is a need to ensure that diversity has been properly calculated. Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 23

2. 2. 5 Final circuit cookers The diversity applicable to the current demand for

2. 2. 5 Final circuit cookers The diversity applicable to the current demand for a cooker is shown as 10 A plus 30% of the remainder of the total connected load, plus 5 A if the control unit includes a socket outlet. A little thought will show that whilst this calculation will give satisfactory results under most circumstances, there is a danger of triggering the protective device under some circumstances. Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 24

2. 3 Loading, maximum demand diversity 2. 3. 1 Connected Load Connected load or

2. 3 Loading, maximum demand diversity 2. 3. 1 Connected Load Connected load or Total Connected Load(TCL) is taken to be sum of all loads in the installation. 2. 3. 2 Diversity Factor Diversity factor, DF is the ratio of the sum of the maximum power demands of the subdivisions, parts of a system, to the maximum demand of the whole system or part of the system under consideration. 2. 3. 3 Maximum Demand Maximum demand (often referred to as MD) is the highest rate at which power is consumed. Alternatively expressed, it is the highest average rate at which electrical is consumed. Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 25

2. 3 Loading, maximum demand diversity Purposes of final circuit fed from conductors or

2. 3 Loading, maximum demand diversity Purposes of final circuit fed from conductors or switchgear to which diversity applies Individual household installations, including individual dwellings of a block Type of premises Small shops, stores, offices and Small hotels, boarding business premises houses, guess houses, etc 1. Lighting 66% of total current demand 90% of total current demand 2. Heating and power (but see 3 and 8 below) 100% of total current demand up to 10 amperes + 50% of any current demand in excess of 10 amperes 100% f. l of largest appliance + 100% f. l of largest appliance 75% f. l of remaining appliances + 80% f. l of second largest appliance + 60% f. l of remaining appliances 3. Cooking appliances 10 amperes + 30% f. l of connected cooking appliances in excess of 10 amperes + 5 amperes if socket outlet incorporated in unit 100% f. l of largest appliance + 80% f. l of second largest appliance + 60% f. l of remaining appliances 4. Motors (other than lift motors which are subject to special consideration) 5. Water-heaters (instantaneous type)* 75% of total current demand 100% f. l of largest appliance + 80% f. l of second largest appliance + 60% f. l of remaining appliances 100% f. l of largest motor + 80% 100% f. l of largest motor + f. l of second largest motor + 50% f. l of remaining motors 60% of f. l of remaining motors 100% f. l of largest appliance + 100% f. l of second largest appliance + 25% f. l of remaining appliances Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 26

2. 3 Loading, maximum demand diversity Purposes of final circuit fed from conductors or

2. 3 Loading, maximum demand diversity Purposes of final circuit fed from conductors or switchgear to which diversity applies Individual household installations, including individual dwellings of a block Type of premises Small shops, stores, offices and business premises 6. Water-heaters (thermostatically controlled) No diversity allowable** 7. Floor warming installations No diversity allowable** 8. Thermal storage space heating installations No diversity allowable** 9. Standard arrangements of final circuits in accordance with Appendix 5 10. Socket-outlets other than those in included in 9 above and stationary equipment other than those listed above 100% of current demand of largest circuit + 40% of current demand of every other circuit 100% of current demand of largest point of utilisation + 40% of current demand of every other point of utilisation Small hotels, boarding houses, guess houses, etc 100% of current demand of largest circuit + 50% of current demand of every other circuits 100% of current demand of largest point of utilisation + 75% of current demand of every other point of utilisation 100% of current demand of largest point of utilisation + 75% of current demand of every point in main rooms (dining rooms, etc) + 40% of current demand of every other point of utilisation Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 27

Example 1 A shop has the following single-phase loads, which are balanced as evenly

Example 1 A shop has the following single-phase loads, which are balanced as evenly as possible across the 400 V three-phase supply. 2 x 6 k. W and 7 x 3 k. W thermostatically controlled water heaters 2 x 3 k. W instantaneous water heaters 2 x 6 k. W and 1 x 4 k. W cookers 12 k. W of discharge lighting (Sum of tube ratings) 8 x 30 A ring circuits feeding 13 A sockets. Calculate the total demand of the system, assuming that diversity can be applied and the power factor is 0. 9. Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 28

Solution The single-phase voltage for a 400 V three-phase system is All loads with

Solution The single-phase voltage for a 400 V three-phase system is All loads with the exception of the discharge lighting can be assumed to be at 0. 9 power factor, so current is calculated as; Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 29

Solution Water heaters (thermostatic) 2 x 6 k. W and 7 x 3 k.

Solution Water heaters (thermostatic) 2 x 6 k. W and 7 x 3 k. W thermostatically controlled water heaters No diversity is allowable, so the total load will be: This gives a total single-phase current of Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 30

Solution Water heaters (instantaneous) 2 x 3 k. W instantaneous water heaters 100% of

Solution Water heaters (instantaneous) 2 x 3 k. W instantaneous water heaters 100% of largest plus 100% of next means that in effect there is no allowable diversity. Single-phase current Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 31

Solution • Cookers 2 x 6 k. W and 1 x 4 k. W

Solution • Cookers 2 x 6 k. W and 1 x 4 k. W cookers 100% of largest 29. 0 A 80% of second 23. 2 A 60% of remainder 11. 6 A Total for cookers 63. 8 A Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 32

Solution Discharge lighting 12 k. W of discharge lighting (Sum of tube ratings) 90%

Solution Discharge lighting 12 k. W of discharge lighting (Sum of tube ratings) 90% of total which must be increased to allow for power factor and control gear losses. Lighting current Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 33

Solution Ring circuits 8 x 30 A ring circuits feeding 13 A sockets. First

Solution Ring circuits 8 x 30 A ring circuits feeding 13 A sockets. First circuit 100%, so current is 30 A 75% of remainder Total current demand for ring circuits = 187. 5 A Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 34

Solution Total single phase current demand = 533. 62 A Since a perfect balance

Solution Total single phase current demand = 533. 62 A Since a perfect balance is assumed, three phase line current Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 35

Example 2 A 240 V domestic cooker has the following connected loads: top oven

Example 2 A 240 V domestic cooker has the following connected loads: top oven 1. 5 k. W main oven 2. 5 k. W grill 2. 0 k. W four hotplates 2. 0 k. W each The cooker control unit includes a 13 A socket outlet. Calculate a suitable rating for the protective device. Calculate the total demand of the system, assuming that diversity can be applied. Assume the power factor, pf is 0. 9. Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 36

Solution The total cooker load is 1. 5 + 2. 0 + (4 x

Solution The total cooker load is 1. 5 + 2. 0 + (4 x 2. 0) k. W = 14 k. W Total current Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 37

Solution The total cooker load is 1. 5 + 2. 0 + (4 x

Solution The total cooker load is 1. 5 + 2. 0 + (4 x 2. 0) k. W = 14 k. W Total current The demand is made up of: the first 10 A 10 A + 30% of remainder + allowance socket outlet Total for 17. 3 A 5 A 32. 3 A Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 38

Exercise 1 The 3 phase supply with 0. 85 pf supply to the small

Exercise 1 The 3 phase supply with 0. 85 pf supply to the small hotel which consist: 3 instantaneous water heater ( 1 – 3 k. W, 2 – 2. 5 k. W) 4 cooker ( 1 – 6 k. W, 2 - 4. 5 k. W, 1 – 2 k. W) 5 florescent (2 – 36 W, 3 – 18 W) 10 downlight 12 W. Calculate the: i. ii. Total Connected Load Current Faculty of Engineering Technology Sept 2014 Universiti Malaysia Perlis 39