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Circuit Breakers Earth Leakage

If you live in an area where the power is supplied by overhead cables, then your earthing will probably be connected to an earth electrode, a copper coated steel road driven into the ground outside your home or office.

Used on its own, however, it is rarely effective. This because of its inability to pass large currents into the soil, particularly during dry weather when the resistance of the soil is very high.

It must be used, therefore, in conjunction with an earth leakage circuit breaker. This device, which is wired to the consumer unit, automatically cuts off any circuit where an earth leakage occurs.

Of the two types of E.L.C.B current and voltage operated it is the current operated one which is generally recommended.. It works on the current balance principle that current flowing into a circuit should be equal to the current flowing out of it. If there is an imbalance, such as occurs when current leaks into the earthing system, then E.L.C.B immediately becomes activated.

Although all E.L.C.B.s operate with great speed and efficiency, not all would provide adequate protection if you touched a live wire while in contact with the ground. Only the high sensitivity E.L.C.B which should be fitted as additional protection to socket outlet circuits, would give some protection in those circumstances.

A current operated type, it can detect just 30 milliamps of earth current and cut the supply within 30 milliseconds which is enough to help prevent a fatal shock to a person touching 240 volt live connection.

A disadvantage of the high sensitivity version is its proneness to nuisance tripping due to small earth leakage currents which may not be dangerous. It is used therefore in circuits supplying power tools and other operated appliances where the risk of electrical shock is high and occasional nuisance tripping does not matter.