Previous: EARTH LEAKAGE CURRENT METER/MONITOR

EARTH LOOP TESTER

Typical Number in Hospital: 3

Cost Bands: 3

References:

In many countries the mains electricity supply is earth referenced. This produces a live conductor which is at a high voltage (e.g. 240 V) above earth potential, and a neutral, which is actually connected to earth at the local substation. The potential on this lead may be a few volts caused by the ohmic loss between the delivery point and the substation. A third conductor is also provided which is connected to earth within the building. The main purpose of the earth conductor is to carry away the large currents which may flow in the event of the live conductor making electrical connection with the metal enclosure of electrical apparatus. The earthing must be of sufficient quality to carry currents well in excess of the fuse capacity to guarantee rapid disconnection of the live supply during faults.

An earth loop tester verifies the integrity of the supply at the substation and within the building by passing a large current (usually 25 A) up the earth lead and back down the neutral lead. This produces a resistance figure for the circuit which will demonstrate whether the earth circuit is capable of blowing the fuses in the live conductor.

Earth loop testers are used by electricians to test the electrical supply installation.