ISOLATING TRANSFORMER

The mains electricity supply has a neutral conductor which is in fact earthed at the local substation, and a live conductor which is approximately 250 V above earth (in Europe). This presents a hazard during accidental contact with the live conductor if a route to earth is provided through the body. A partial solution to this problem can be provided for situations where equipment must be opened while connected to the mains by the inclusion of an isolating transformer in the mains supply. This creates a new mains supply which has neither conductor connected to earth so that risk of electrocution only occurs if both conductors are touched simultaneously. The transformer has two identical but isolated windings.

Isolating transformers are often used on benches where electrical or electronic equipment is serviced. They are less used now since the introduction of earth leakage circuit breakers (ELCBs) or residual current circuit breakers (RCCBs) which detect the difference in current in the two supply leads and disconnect the supply if this exceeds preset limits.

Content and Design Copyright 2000 Dr. Malcolm C Brown.  See Title Page for more details