Next: EARTH LEAKAGE CURRENT METER/MONITOR

EARTH LEAKAGE CIRCUIT BREAKER (ELCB)

Typical Number in Hospital: 50

Cost Bands: 1

References: 2

The earth wire in a three wire mains supply is to conduct away any small leakage currents, and also to provide a low resistance path to earth from the case of instrument and cause a fuse to blow if a short circuit should occur inside the equipment. The ELCB monitors the current flowing to earth, usually by measuring the difference between the currents flowing in the live and neutral wires. If this exceeds a preset limit a relay operates to disconnect the supply. The current limit is set to be well above the normal leakage current of the equipment but sufficiently low that the relay can disconnect the supply so quickly that electrocution is avoided.

Since the leakage current is not measured in the earth wire the same principle can be applied to a two-wire supply to a double insulated device. If a fault occurs so that current flows to earth (e.g. through the patient or operator) the supply is disconnected before any harm is done. An ELCB can be incorporated into a mains plug or lead, or may be permanently installed as part of the mains supply. These are coming into very common use now in hospitals and are sometimes called residual current circuit breakers.