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General Requirements in the NEC

Interrupting Ratings

Interrupting Ratings

Section 110.9

Section 110.9 is a more specific requirement than the previous sections. It addresses interrupting ratings, which are the ratings of equipment intended to interrupt current at fault levels, as opposed to a switch or other device that is only intended to turn a piece of equipment on or off under normal load currents.

The definition of interrupting rating is found in Article 100.

Interrupting Rating. The highest current at rated voltage that a device is identified to interrupt under standard test conditions.

Informational Note: Equipment intended to interrupt current at other than fault levels may have its interrupting rating implied in other ratings, such as horsepower or locked rotor current.

Fuses or circuit breakers that do not have adequate interrupting ratings could rupture while attempting to clear a short circuit. Interrupting ratings should not be confused with short-circuit current ratings, which are further explained in Section 110.10.

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

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