Maximum Phase Fault Current Calculation

The total impedance is the sum of the impedances of the conductors from the origin of the installation to the circuit under consideration. For single phase circuits, the maximum fault current is between the phase and the neutral and in three phase circuits it is when all phases are shorted (symmetrical current). The total impedance is that with operating temperature 20οC (lower temperature means lower resistance).

In particular:

For single phase circuits:

For three phase circuits:


the phase to neutral voltage

the impedance corrected at 20 oC

the impedance of the phase conductor

the impedance of the neutral conductor

the external impedance (from the starting point of the circuit up to the origin of the installation)

The voltage factor Cmax is to take into account the worst case voltage variations conditions in a low voltage installation, specified in BS EN 60909 as 1.1 (optional factor)

Protective Device Breaking Capacity Check

The software acts according to regulation (434.5.1), to check the Breaking Capacity of the protective device: