I am installing a 150 amp sub panel in a customer's house. I am working on sizing the conductors for this. This may be a dumb question but I do mostly commercial and i have always use tbl 310.16 to size conductors. As I looking though the code book I came across table 310.15. So my question is which table do I look at for this sub panel. I know I should know the answer but I just want to be sure I am thinking of using table 310.16 thanks for any help.
Question about a residential sub panel
- Thread starter jm1470
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- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Imo if the feeder to the sub panel carries the entire load of the house then I would say you can use 310.15 otherwise it is 310.16
bobserrano
Member
- Location
- Silicon Valley, California
Table 310.15(b)(6) is used for dwelling services and feeders. Since the subpanel is served by a feeder, (see definition of feeder in article 100), 310.15(b)(6) is the correct table to use.
triplstep
Member
- Location
- Aurora, Illinois
Agree, it is the correct table to use, if feeding the main panelboard,
Table 310.15(B)(6), shall be permitted as 120/240-volt, 3-wire.......feeder conductors that serve as the main power feeder to each dwelling unit ........ the main power feeder shall be the feeder(s) between the main disconnect and the lighting and appliance branch-circuit panelboards(s).
Table 310.15(B)(6), shall be permitted as 120/240-volt, 3-wire.......feeder conductors that serve as the main power feeder to each dwelling unit ........ the main power feeder shall be the feeder(s) between the main disconnect and the lighting and appliance branch-circuit panelboards(s).
As metioned earlier, 310.15(B)(6) can only be used if the panel is the Main Panel, (not to be confused with the Main Disconnect)
310.15(B)(6) can not be used for all sub-panels in a residential application.
Roger
Mvillines
Senior Member
- Location
- Western KY on the Ohio River
Correct 310.15(B)(6) can not be used in sizing conductors serving sub-panels where the sub-panel does not serve the entire load of the house, however, a sentence from 310.15(B)(6) “The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity greater than their service-entrance conductors.” first showed up in the 96 code cycle because of be penalize were the feeder conductors could be larger than the service conductors.
If you had a 200 amp service panel serving house loads and a 150 amp OCPD serving the sub-panel table 310.16 would be the one to use. If you had a 150 amp service panel and the service entrance conductors are sized by 310.15(B)(6) there would be no requirement to up size the feeder conductors to table 310.16. So you are not really using table 310.15(B)(6) but complying with the text of 310.(B)(6). This applies whether the feeder supplies the entire load or not.
If you had a 200 amp service panel serving house loads and a 150 amp OCPD serving the sub-panel table 310.16 would be the one to use. If you had a 150 amp service panel and the service entrance conductors are sized by 310.15(B)(6) there would be no requirement to up size the feeder conductors to table 310.16. So you are not really using table 310.15(B)(6) but complying with the text of 310.(B)(6). This applies whether the feeder supplies the entire load or not.
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