Hello Everyone:
I have a question regarding replacing some existing panelboards.
While replacing 600A, 480/277V panels it was found that the panels have (2) sets-500 MCM conductors per phase, however, the neutral is only 1/0AWG per panel. The contractor claims this is an NEC code violation [NEC 310.10(H)(2) Section for parallel conductors] and he wants to pull 500KCMil for neutral feeders to make them code compliant. My understanding we can reduce the neutral conductor size based on the unbalance load, however, since they are parallel runs, the minimum size neutral shall not be less the #1/0 which what we have. Per the panel schedule, most the loads are 3-phase motors, transformers, UPS by pass and many unknown loads but all fed from 3-Pole breakers. Is this a code violation assuming we do not have a lot of 277V? I will ask the contractor to verify these unknown loads to ensure they don’t feed any 277V loads.
Thanks,
I have a question regarding replacing some existing panelboards.
While replacing 600A, 480/277V panels it was found that the panels have (2) sets-500 MCM conductors per phase, however, the neutral is only 1/0AWG per panel. The contractor claims this is an NEC code violation [NEC 310.10(H)(2) Section for parallel conductors] and he wants to pull 500KCMil for neutral feeders to make them code compliant. My understanding we can reduce the neutral conductor size based on the unbalance load, however, since they are parallel runs, the minimum size neutral shall not be less the #1/0 which what we have. Per the panel schedule, most the loads are 3-phase motors, transformers, UPS by pass and many unknown loads but all fed from 3-Pole breakers. Is this a code violation assuming we do not have a lot of 277V? I will ask the contractor to verify these unknown loads to ensure they don’t feed any 277V loads.
Thanks,