Testing prospective fault current (regulation 612.11)
In some installations prospective fault currents can be tens of thousands of amps. Needless to say, many protective devices would be damaged by such high currents and may even fail catastrophically, putting the premises in danger. People need to be able to establish a value for the maximum fault current that could be present at each protective device and verify that the device is suitably rated to cope with this current. The prospective fault current is measured at the origin of the installation because this is where the maximum fault current will occur. As one moves downstream within the installation the prospective fault current will get less. It is also usual to measure the prospective fault current at each distribution board to verify that the protective devices are capable of handling this current. There is often much confusion about the terms used to describe prospective fault current.