sizing feeder

[iwire]

Bob
so you really think we all have been doing it wrong prior to the 2002 code?

I think many areas have misinterpreted it since at least 96 and maybe 93.

In the 1990 NEC the section was shorter and basically said, you could use the table for feeders and services in dwelling units. So under the 1990 NEC I agree it could be used for sub panel feeder sizing.

I don''t have the 93, so I don't know what it said then but in the 1996 NEC I find the words "that serve as the main power feeder to a dwelling unit"


Once we get to the 99 NEC they added more explanation.

"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)."

If anyone has the ROPs for those code years we could get to the bottom of this. As far as I know those ROPs are not online so someone would have to have them at home on paper.

 

[Sierrasparky]

Bob,
I don't want to beat a dead horse.
I just don't understand what is meant by Feeders(S) panelboard (S) here and in earlier codes. Why the plural?
We use panels here without banch breakers outside due to large acumulations of snow. So any panel directly fed from panel with the Main breakers will be between the main and the" Branch Circuit/Lighting panelboard. "
I have yet to see multiple feeders other than parrallel that supply multiple panelboards and do not carry 100% of the load.

I don't think ther were thinking of a situation like this
Main- panelboard-feed through feeder -panelboard in this case the other rule would apply. this would make this whole thing redundant.
My take is that they just wanted to make Nm and SER have the same ratings.

I don't get why we have to size a Service entrance conductor properly but the POCO can reduce the size due to what the EC gives them is a load calc. The only time you get them to increase the size is if you call them on exessive flicker .

 

[Bjenks]

Iwire
I'm not selling this application either way. In the past we seem to have agreed with your reasoning. I happened, in this case, to read NEC 2005 310.15(B)(6) a little closer and quoted it as reading This portion of (6) seems to define the power feeder as
the FEEDER(S) between the main disconnect and the lighting and appliance branch circuit PANELBOARD(S).
If you except this definition, then dual feeders and dual panels should be accepted. It likely will lie with the inspection dept. I really do not see a technical reason for the change. Large homes do have more that one panel.
Iwire, what was the problem the CMP had with this type on installation?

It gets better defined in 2008... Now it says just panelboard instead of lighting and appliance panelboard. It also now says feeder instead of feeder(s), but it then adds a point of clarification and says "all loads that are part or associated with the dwelling unt."

In 2005 I went with the feeder that feeds 100% of a dwelling unit rule. Now it seems to say any feeder feeding part of the unit which to me means any multiple of feeders that are more than 100A.

BTW: several have mentioned only being able to use 60 degree wire, but I don't see any code reference for that requirement unless the terminals are rated at 60 degree. An I line panel and it breakers are rated at 75 degree and would assumre the 200A panels MLO would be too.