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NOTE: This is an unformatted excerpt from our online fire protection training library.

General Requirements in the NEC

Short-Circuit Current Ratings

More on Faults

To prevent extensive damage from short circuits and ground faults, it is necessary to determine how much current could possibly flow in a circuit, based on the capacity of the source and the amount of impedance in the circuit up to the point of the fault.

Based on how much current is actually available, equipment can be selected that is capable of interrupting that much fault current, such as a circuit breaker or a fuse. This type of equipment would be required if the intention is to interrupt current at fault levels.

Short circuits and ground faults typically occur because of some kind of damage to a conductor that keeps the insulation from working properly. In either case, a very high current results, because the impedance of the circuit is dramatically lowered.

Overcurrent protective devices (such as fuses and circuit breakers) should be selected to ensure that the short-circuit current rating of the system components is not exceeded should a short circuit or high-level ground fault occur.

NOTE: This is an unformatted excerpt from our online fire protection training library.

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