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How do I size the circuit breaker for a generator to comply with NEC 695.4(B)?

NEC 695.4(B) points back to NEC 430.62 for sizing the overcurrent device for the generator fed fire pump. Remember that if the fire pump is fed by a service, the breaker is sized to carry locked rotor (approx 6 times FLC) indefinitely. Where a generator serves the fire pump, NEC 430.62 permits you to use the values in Table 430.52 instead of setting the breaker at locked rotor (Approx 6 times FLC). Table 430.52 sizes the breaker at a maximum of 250 percent of the largest motor. Then I must add the FLC of all the other motors (jockey pumps) that are being fed by the generator. The NEC does NOT permit using an instantaneous-only circuit breaker such as the Mag-Gard. ALAN MANCHE


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