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Subject - Residential Feeders
David Hyatt Article 310.15(6) How do you interpret this article? I see that any feeder to a branch circuit panel, whether or not, its a main disconnect or sub-feed panel will be sized by TBL 310.15. Is this true? Are they any exceptions?
JimmyDee (6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders. For dwelling units, conductors, as listed in Table 310.15(B)(6), shall be permitted as 120/240-volt, 3-wire, single-phase service-entrance conductors, service lateral conductors, and feeder conductors that serve as the main power feeder to a dwelling unit and are installed in raceway or cable with or without an equipment grounding conductor. For application of this section, the main power feeder shall be the feeder(s) between the main disconnect and the lighting and appliance branch-circuit panelboard(s). The feeder conductors to a dwelling unit shall not be required to be larger than their service-entrance conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.22, and 230.42 are met.
May be wrong but I don't see this as a feeder that is a sub feed off from a main service panel. I see this as a feeder that is feeding a main lighting panel for a dwelling unit. Sub panels would be required to be fed by wire that complied to 310.16
Jim
David Hyatt Thats what I am not sure about, Jim. Say you have a main panel with various breakers in it and are sub feeding a lighting panel. It seems to me you could size with TBL 310.15.
When I wire a trailer 200amp 8 circuit main with feed through lugs the wire I used to feed the trailer is sized from that TBL. This is an unclear subject and over the years this section has been reworded, but still not clear. I look forward to hearing all input on this subject. Also if you have to use TBL 310.16 for 200amp sub-feed the wires would be larger than the service conductors. 310.15 (6) says that they are not required to be larger than the service entrance conductors. I think they worded it this way to included sub-feeds?
JimmyDee
quote:
310.15 (6) says that they are not required to be larger than the service entrance conductors.

This statement is my clue that you have to use 310.16 because why would they say "not required to be larger than the service entrance conductors" if they were not talking about a different standard for sub panel feeders?
Jim
Dave Nix Hi Jimmy,

This drawing from the NEC Handbook will help.
quote:
Service-Entrance Conductors, Overhead System. The service conductors between the terminals of the service equipment and a point usually outside the building, clear of building walls, where joined by tap or splice to the service drop.

JimmyDee Dave,
I'm not sure what you are referring to in your post. I can assume it is a picture of the service conductors? It is my understanding that the service conductors start at the service drop splice point and enc at the main service disconnect.
The service conductors are allowed to be reduced in size (probably because of demand) but the point I was making if a sub panel feed were to come off from a panel and it was the same ampacity as the feeding panel, the wire size of the sub panel would not have to be full sized, it could be sized the same as 310-15 (6).
Jim
Dave Nix Hi Jimmy,

Yes, you are correct. I am agreeing with you!
When looking at the drawing, be sure and see the difference in the wires with the arrows describing which is which.
JimmyDee I know this one well because one of the multiple guess questions on a test I give is is "What is a service drop?" and one of the answer choices is "when the power company drops your service for non payment" It is surprising the number that go for this answer.
Jim
Dave Nix Good one Jimmy!