In single-phase motor installations, the branch-circuit protection is based on NEC Table 430.52 as a percentage of full-load current. (Note: Full-load current referred to here is the Code book value.) The full-load current is listed in Table 430.248 for single-phase motors. If using a typical inverse time breaker, the percentage for single-phase motors is 250% of the Code book value for the size of the motor at the connected voltage. Briefly explain why this high percentage is allowed.
What will be an ideal response?
This high percentage is allowed so that the breaker does not trip every time the motor starts, as the motor draws many times the rated current as it starts. The high percentage is considered proper to protect the wiring from short circuit, and faults to ground in the branch circuit conductors.
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