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Size sub panel for each apartment in a 3 family house

Posted by fotostat (My Page) on
Wed, Nov 18, 09 at 11:04

In a 3 family house there are three main panels in the basement, one for each apartment. Some circuits are taken out of those panels, but there is also a sub panel inside of each apartment that the rest of the circuits are taken out of.

Is there any calculation that needs to be done to determine the size of that sub panel?

Right now the panels are fed with a 12-2 (that's right, single leg) and there has never been a problem.

The panels need to be upgraded, would it be alright to refeed them with 10-3, which should be more than enough ampacity for them? Or should it be bumped up to 8-3 just to be safe?


Follow-Up Postings:

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RE: Size sub panel for each apartment in a 3 family house

Just so you know all (or at least the vast majority of) municipalities prohibit unlicensed persons from doing electrical work in multi-family dwellings. You really need to hire a licensed electrician who could answer your questions and ensure the work is done safely and to code.


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RE: Size sub panel for each apartment in a 3 family house

Thanks for the info, but my area of PA doesn't require contractor licensing.

FWIW, I am an electrician, but I do commercial work and unfortunately, as an IBEW member, our apprenticeship and continued work doesn't deal with the code all that much. Most of the code issues are dealt with by the engineers, very little is left for us to decide, some people call us "electrical installers" which is true to a point.

On an issue like this thread topic, I'd be happy to learn if people could help by citing the code or giving opinions.


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RE: Size sub panel for each apartment in a 3 family house

There's a table in Article 220.49 that might help with the load calculations. Properly sized feeders is covered in Article 215.2 and you can find wire ampacity tables Article 310.16.

Hope this helps!


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RE: Size sub panel for each apartment in a 3 family house

220.49? I don't see that in 05 or 08.

In 310.16 where is NM listed?


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RE: Size sub panel for each apartment in a 3 family house

Bump...


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RE: Size sub panel for each apartment in a 3 family house

220.49? I don't see that in 05 or 08

Maybe Mike meant Table 220.42 ??

In 310.16 where is NM listed?

Cable types aren't listed, only wire sizes. See 334.80 which says to use the 60C columns in 310.16 for NM to select wire ampacity. (In other words size NM the same as TW, UF.)


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