According to Ohm’s Law, the current flowing during a fault is equal to the supply voltage divided by the total impedance of the fault loop (I = V / Z). If the loop impedance is too high, the fault current will be too low. A low fault current might not trip a circuit breaker or blow a fuse quickly—or at all. This is dangerous because the metal casing of a faulty appliance could remain live indefinitely, waiting for someone to touch it.
. The simplified formula for calculating the required impedance to ensure safety is:
If the impedance is too high, the fault current will be too low. This is dangerous because:
