cdcengineer
Senior Member
I have a question, let's hope I can verbally describe this adequately for the sake of this discussion.
The distribution is 208Y/120V, 3-phase, 4-wire and the conduit contains conductors to serve (4) 20A, 120 receptacles and (4) 50A, 208V receptacles. Because the 50A receptacles are 3-wire served from a 3-phase system, I must consider the grounded or neutral conductors as current carrying when applying the demand from table 310.15(B)(3)(a) per NEC 310.15(B)(5).
Therefore, I have underground PVC-sch 40 conduit with (16) current carrying conductors derated 50%. I am specifying THWN-2 copper conductors. Do I apply the demand of 50% to the ampacity of the 90 deg C column of table 310.15(B)(16)? And if so, (without considering voltage drop) would I need a minimum of #10 AWG CU for the 20A and #3 AWG CU for the 50A receptacles respectively?
Thanks for your input.
The distribution is 208Y/120V, 3-phase, 4-wire and the conduit contains conductors to serve (4) 20A, 120 receptacles and (4) 50A, 208V receptacles. Because the 50A receptacles are 3-wire served from a 3-phase system, I must consider the grounded or neutral conductors as current carrying when applying the demand from table 310.15(B)(3)(a) per NEC 310.15(B)(5).
Therefore, I have underground PVC-sch 40 conduit with (16) current carrying conductors derated 50%. I am specifying THWN-2 copper conductors. Do I apply the demand of 50% to the ampacity of the 90 deg C column of table 310.15(B)(16)? And if so, (without considering voltage drop) would I need a minimum of #10 AWG CU for the 20A and #3 AWG CU for the 50A receptacles respectively?
Thanks for your input.