Electrical Wiring means to connect the electric load to the supply mains, according to the Electricity rules.
The electrical energy is used in houses for lighting and other purposes whereas in industries it is used for power and lighting purposes. So the wiring is either single phase or three phase.
AC single phase or DC wiring. This wiring is used in houses for lighting and power purposes. It can be A.C. single phase or D.C. wiring. In case of D.C. wiring there are two wires positive and negative. The load is connected across these wires through proper controllings and safety devices. In A.C. single phase the phase and neutral are connected to the load through proper controlling and safely accessories. The third wire is an important wire i.e. earth wire in both A.C. or D.C. systems. The earth wire is connected to the all metallic portions of the wiring and appliances except the current carrying conductors.
Three phase wiring. The three phase wiring is used for three phase power load and for single phase loads also. In A.C. single phase loads to be connected on three phase system, every individual phase is connected across three independent circuits, the total load is divided into three balanced circuits, generally three phase four wire system is used. In case of three phase power loads the line voltage is 400/440 volts. The three phase load may be in star or in delta. The single phase circuit is connected across 220/230 volts, across one phase and neutral.
A simple arrangement is shown in Fig. 14.1. The supply is taken from the distribution line through service mains. A pole fuse is provided, the function of which is to protect the service line against over loading. The supply is directly fed to the energy meter and after the energy meter a service fuse, which is generally an iron clad fuse. is provided for the safety purpose. The iron-clad cutout and energy meter are the property of the supplier. So both are sealed by the supplier. The mains are taken from the energy meter and are controlled by means of neutral linked I.C.D.P. main switch. If the load is more and has to be divided into a number of circuits, the distribution boards and boxes, depending upon the circuits required are used e.g. two ways, three ways, four ways etc. One phase and one neutral is taken for independent circuits. If it is required, depending upon the load, the sub-distribution boxes may be used. Thus in this arrangement the pole fuses, distribution boards, earth wire are the essential elements which are illustrated in Fig. 14.1. The earth continuity is maintained throughout the installation.
Fig. 14.1. Method of supply.
What are the methods of installing the service mains?
Ans. There are two methods of installing the service mains:
(a) Overhead service line system.
(b) Underground service line system.
(a) Overhead service line system. In this case the service mains runs over the height. Depending upon the prevailing conditions the over head lines are:
(i) For double and multistoried buildings. In this case a bracket is embedded into the wall on a suitable height and then the line is installed and taken to the energy meter. Generally weather proof wire or PVC. cable is used for this installation, this cable is known as service cable. The G.I. pipe is bend back to prevent the unwanted water entry into the pipe.
(ii) Single storeyed building. In this case a G.I. pipe is raised above the roof to a suitable height and fixed with wall with clamps. Similarly the pipe is bend back to prevent the water entry into the pipe. From the service bracket the service cable is taken to the meter.
(iii) Weather proof cable and p. V.C. cable method. In this method the service main is not of the bare conductors as described in method I and Il, but are insulated weather proof or P.V.C. cables. It is used for high buildings, road crossing etc. In this case an 8 S.W.G. G.I. wire is stretched from the service pole to an eye bolt fixed to the wall. The insulated cable is clipped to this G.I. wire by means of clips or binding wires.
(b) Underground cable. In this system the supply is taken through the U.G. cable and is taken to the energy meter through trench. Cable is held on the pole by means of the pole clamps. The cable box is used to concept the underground cable to the distribution line. The trench starts from the pole and terminates vertically below the service board.
What are the different systems of wiring distribution?
There are the following main systems of wiring (connections) system:
(a) Tree system.
(b) Distribution board system.
(a) Tree system. Figure 14.2 shows an arrangement of this system. In this system the main supply line runs along the building. A number of tappings are taken from the main line for different circuits.
There are the following advantages and disadvantages:
Advantages: It is less costly.
Disadvantages:
(i) The voltage across the appliances does not remain constant. The voltage near the supply main circuit will have more voltage than the voltage at a far circuit.
(ii) The fuses of the different circuits are at different places.
(iii) The tappings can be loose and fault location is not easy.
(iv) The main supply wire are bigger size. This system is not used generally.
Fig. 14.2. Tree system.
Fig. 14.3. Distribution system.
(b) Distribution board system. This system is mostly used at present. In this system all the appliances etc. are connected across the same voltage. The leads from the main switch are taken to the copper strip in a main distribution board. There are a number of fuse provided in the box, from where the different circuits can be drawn. If the load is more, then the sub-distribution boxes are also used. The line goes from the main to sub-distribution box and then to the individual load circuits as shown in Fig. 14.3. Nowadays, instead Of fuse cutouts the MCB are preferred. The fuse is being replaced by MCB and neutral is connected with the neutral link. Thus separate cireuits one drawn and all are controlled independently by the individual MCB. There are the following advantages and disadvantages Of this method:
Advantages:
(i) All the loads are connected across the same voltage.
(ii) Fault location is easy.
(iii) The fuses are at one places.
(iv) Appearance is good.
(v) Extension is easy.
Disadvantages:
(i) Costly than the tree system.
(ii) Skilled labour is required.
What are the different methods of connections to the accessories?
Ans. There are the following two methods of connections:
(a) T-connections.
(b) Looping in system.
T-Connections. In this system the connectors, joints cut-outs, three plate ceiling rose etc. are used as shown in Fig. 14.4.
There are the following advantages and disadvantages:
Advantages:
(i) Less wire is required.
(ii) Less cost.
(iii) Less voltage drop in the wires and less power loss in the wiring.
Disadvantages:
(i) A number of joints are is the wiring. The joint is the weakest point of the installation.
(ii) The joint may be loose and so the faults are frequent and the fault location is not so easy.
(b) Looping is system. In this system the connector etc. are not used but the connections are made as shown in Fig. 14.5 from the switches or batten holders.
There are the following advantages and disadvantages:
Advantages:
(i) There are less number of joints.
(ii) Good insulation resistance of the wiring.
(iii) Appearance is good.
Disadvantages:
(i) A greater length is required.
(ii) It is costly than the tree system.
(iii) More voltage drop and power loss in the installation.
(iv) Because of more wires in the conduit or casing and capping etc. The fault location is not so easy.
(v) Looping in switches and holders terminals is usually difficult.
Fig. 14.5. Looping in system.
