innersurffer
Member
Which chart should be used in the following situation? 310.15(B)(6) or 310.16?
I installed a 35Kw (146.5 amp) generator with a 175 amp breaker on the generator. The generator goes to a ATS that is connected by a main disconnect that is fed from the meter. The generator was installed at a single family home and the estimator (commercial and residential) used 310.15(B)(6) to size the wire at 1/0 AWG copper. The NEC Code Handbook ( i know, just use the code book) says:
....one-family...the reduced conductor size permitted by 310.15(B)(6) is applicable to the service-entrance conductors, service-lateral conductors, or any feeder conductors that supply the main power feeder to a dwelling unit (i.e. the generator becomes the main power feeder).
My head Commercial manager says we should have used 310.16 and the lug temperature rating (which i am more acclimated with) and in this case with the 75 degree lugs would have been 2/0 AWG copper.
I understand where both are coming from and have more of a background in commercial. The residential chart does have the ability to be used for reduced conductor size and seems to throw out the lug temperature (usually the weakest point) out the window. On the other hand, this house will never see 175 amps considering the generator will never produce more that 146.5 amps. Some experienced EC want to help another EC figure this one out? What if I really needed all 175amps or had to rate this to its potential to produce based on the breaker? Please clarify these charts. Give code references if possible.
I installed a 35Kw (146.5 amp) generator with a 175 amp breaker on the generator. The generator goes to a ATS that is connected by a main disconnect that is fed from the meter. The generator was installed at a single family home and the estimator (commercial and residential) used 310.15(B)(6) to size the wire at 1/0 AWG copper. The NEC Code Handbook ( i know, just use the code book) says:
....one-family...the reduced conductor size permitted by 310.15(B)(6) is applicable to the service-entrance conductors, service-lateral conductors, or any feeder conductors that supply the main power feeder to a dwelling unit (i.e. the generator becomes the main power feeder).
My head Commercial manager says we should have used 310.16 and the lug temperature rating (which i am more acclimated with) and in this case with the 75 degree lugs would have been 2/0 AWG copper.
I understand where both are coming from and have more of a background in commercial. The residential chart does have the ability to be used for reduced conductor size and seems to throw out the lug temperature (usually the weakest point) out the window. On the other hand, this house will never see 175 amps considering the generator will never produce more that 146.5 amps. Some experienced EC want to help another EC figure this one out? What if I really needed all 175amps or had to rate this to its potential to produce based on the breaker? Please clarify these charts. Give code references if possible.