Fire Pump Grounding

[timm333]

What should be the conductor size to ground 100HP 208V fire pump? The fire pump is fed directly from the 208V secondary of the transformer. There is no overcurrent protection in between transformer secondary and fire pump. However there is 30A circuit breaker on the primary side (12.47kV) of the transformer.


The 30A at 12.47kV equals 1800A at 208V. So if we size the ground conductor using NEC table 250.122, the required ground conductor size will be 250MCM. Is it correct?

 

[waross]

My code is based on the ampacity of the largest ungrounded conductor or equivalent for multiple parallel conductors.
250 MCM is good for grounding ampacities up to 2000 Amps. More than that and you have to use 350 MCM.

Bill
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