5.3What is a residual current device?#

An RCD is a ‘mechanical switching device designed to make, carry and break currents under normal service conditions and to cause the opening of contacts when IΔ (the residual current) attains a given value under specified conditions’ (AS/NZS 3190). In other words, the RCD is a circuit breaker that senses when the active and neutral currents in a circuit are not equal and, when that inequality reaches a predetermined value for a predetermined time, opens the breaker contacts. These devices have also been called ‘safety switches’ and ‘earth leakage circuit breakers’.