Page 928 - Basic Electrical Engineering

Electricity distribution authorities supply power to the consumers at the
following two voltages. Single-phase supply: 230 V, 50 Hz, two-wire, three-
phase supply: 415 V, 50 HZ, four-wire. In a two-wire single-phase supply

there is one phase or live wire and the other is called the neutral wire. Single-
phase supply is required for electrical appliances like fan, tube light, lamp,

washing machine, refrigerator, electric iron, room heater, room air-
conditioner, kitchen electrical appliances like mixer, grinder, microwave

oven, etc.
In a four-wire, three-phase supply, power is supplied through three live

wires and a neutral wire. The neutral wire is normally at zero potential and is
earthed at the substation. Three-phase loads like three-phase induction motors
used for water lifting are supplied with three-phase supply. In such a case all

the phases get equally loaded. Three-phase supply can also be used to feed
single-phase loads as shown in Fig. 13.10. Single-phase electrical loads are

connected between the phase or live wires and the neutral wire in such a way
that all the phases are equally loaded.

As shown in Fig. 13.10, supply from the secondary of a three-phase
transformer is taken through feeder wires to the busbars (busbars are thick

copper strips). From the busbars both single-phase supply and three-phase
supply are taken out and are connected to the loads.

13.9.1 Service Connection

Electricity supply authorities supply power to the domestic loads, i.e.,

residential houses through a low-voltage three-phase four-wire distribution
system. The distribution system is formed either through overhead lines or

through underground cables. In modern cities, only underground cables are
used for electric power distribution system. From the electricity supplier’s

distribution system, power is brought to the premises of the consumer
through a cable called the service line or service connection. The service line

is normally an underground PVC cable. The service cable is brought to the
consumer’s distribution board.