Guarding implies the use of an added low impedance conductor, maintained at the same potential as the high impedance circuit, which will intercept any interfering voltage or current.

The short circuit current calculation is required for choosing equipment and current carrying conductor, setting of the rely and automation, confirmation of the short circuit current limiting method.

Acknowledge and in time effective protection of power semiconductors from fault current is of utmost importance for the reliable operation of AC equipment on electric locomotive.