Introduction
In the presence of an insulation fault, the fault current ld is only limited by the impedance of the fault loop cables. For 230/400 V networks, this voltage of the order of
(if
) is hazardous as greater than the limit safety voltage, even in dry environments (
= 50 V). It is then necessary to ensure automatic and immediate de-energising of the installation or part of the installation. As the insulation fault is similar to a phase-to-neutral short-circuit, breaking is achieved by the overcurrent limiting devices.
The calculation of a short circuit current can be complicated.
In fact it is the combination of Direct, Inverse and homopolar vector currents.
Three simplified method exist to calculate the value of the short circuit.
