Service Neutral Sizing

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I am designing a 1600 amp service for a waste water treatment plant. The service entrance conductors consist of four sets of 3#600Kcmil, 1#? Neutral and 1 #4/0 gnd from a utility pad mounted transformer. The neutral load consists of the imbalance associated with 277V LED lighting and four small 277V heat pump motors. The connected (not unbalanced) load for these 277V loads is approximately 55 amps. Most of the loads are balanced three phase motor loads with more than half of the motor load being driven by VFD's. All other 480V loads are three phase serving 480 to 120/208 three phase transformers generally feeding single phase loads. I don't think I need a fully rated (600KCMIL) neutral and I don't see anything in the code that stipulates a neutral size except for maybe 250.24 C2 which says the grounded service conductor cannot be any smaller than 1/0. Any opinions?
 

david

Senior Member
Location
Pennsylvania
I am designing a 1600 amp service for a waste water treatment plant. The service entrance conductors consist of four sets of 3#600Kcmil, 1#? Neutral and 1 #4/0 gnd from a utility pad mounted transformer. The neutral load consists of the imbalance associated with 277V LED lighting and four small 277V heat pump motors. The connected (not unbalanced) load for these 277V loads is approximately 55 amps. Most of the loads are balanced three phase motor loads with more than half of the motor load being driven by VFD's. All other 480V loads are three phase serving 480 to 120/208 three phase transformers generally feeding single phase loads. I don't think I need a fully rated (600KCMIL) neutral and I don't see anything in the code that stipulates a neutral size except for maybe 250.24 C2 which says the grounded service conductor cannot be any smaller than 1/0. Any opinions?

....................... and 1 #4/0 gnd from a utility pad mounted transformer...........................

What is the #4/0 being used for, how are they connected at both ends?
 
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