200% neutrals

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we have a 15 kva k rated transformer serving a 120/208volt 3 phase panel board with a 50/3 main circuit breaker. we know the unground phase conductors would be 3#8, but what size and how many grounded conductors(neutral) would be requires
 

RB1

Senior Member
Only one neutral is required. The ampacity should be 200% of the ungrounded conductors. Be careful though, when these conductors are derated per 310.15(B)(2) and 310.15(B)(4) the No. 8 will not be permitted to terminate a 50-amp circuit breaker per 240.21(C)(2).
 
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