<P> In an electric power system, a fault or fault current is any abnormal electric current . For example, a short circuit is a fault in which current bypasses the normal load . An open - circuit fault occurs if a circuit is interrupted by some failure . In three - phase systems, a fault may involve one or more phases and ground, or may occur only between phases . In a "ground fault" or "earth fault", current flows into the earth . The prospective short - circuit current of a predictable fault can be calculated for most situations . In power systems, protective devices can detect fault conditions and operate circuit breakers and other devices to limit the loss of service due to a failure . </P> <P> In a polyphase system, a fault may affect all phases equally which is a "symmetrical fault". If only some phases are affected, the resulting "asymmetrical fault" becomes more complicated to analyse . The analysis of these types of faults is often simplified by using methods such as symmetrical components . </P>

What is meant by fault in power system