Thecable bringing the mains electricity supply into a house contains twowire – live and neutral. The neutral wire is earthed at the localtransformer substation, so it is at earth potential. At someconvenient place inside the house the service cable enters a sealedbox where the live wire is joined to the Electricity Board's fuse.
The supply is controlled at the intake by a Consumer's ServiceUnit, which consists of a large main double pole switch combined witha single pole fuse or an earth leakage contact breaker for each ofthe lighting circuit, cooker circuit, water heater circuit and ringcircuit.
In modern domestic installations the power circuits are tapped offa ring circuit. This is a cable which passes through the variousrooms of the house and has both pairs of conductors connected to onefuse. There are therefore two paths to any particular circuit. Eachappliance in the circuit is fitted with a fuse.
All fuses are placed in the live side of the supply ensuring thatif a fuse blows the circuit is dead and it is not possible to receivean electric shock.