What Is the Intent of NEC 110.9 and 110.10

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The Answer is The student must understand the intent of NEC 110.9 and 110.10.That is, ensure that the fuses and/or circuit breakers selected for an installation are capable of interrupting the current at the rated voltage under any condition (overload, short circuit, or ground fault) with complete safety to personnel and without damage to the panel, load center, switch, or electrical equipment in which the protective devices are installed.
An overloaded condition resulting from a miscalculation of load currents will cause a fuse to open or a circuit breaker to trip in a normal manner.However, a miscalculation, a guess, or ignorance of the magnitude of the available short-circuit currents may result in the installation of breakers or fuses having inadequate interrupting ratings.Such a situation can occur even though the load currents in the circuit are checked carefully.Breakers or fuses having inadequate interrupting ratings need only be subjected to a short circuit to cause them to explode, resulting in injury to personnel and serious damage to the electrical equipment.The interrupting rating of an overcurrent device is its maximum rating and must not be exceeded.

What Is the Intent of NEC 110.9 and 110.10

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