Is a 100 subpanel the right choice

rjs625December 22, 2011

Hey was hoping someone could help,

I purchased a two unit house a little over a year ago and am looking to completely rewire the house. Currently I have a 100A box in the basement that has 3-4 large lines coming upstairs and then branching to multiple outlets and lights.

I want to put a 100A panel upstairs in a utility room that will be about 30ft directly above the panel in the basement. My father, who is not an electrician but very handy and wired his house as he remodeled, suggests feeding a 100A panel using a 100A breaker in the box that's in the basement. This would allow us to run new circuits off the upstairs box and abandon the corresponding circuits in the basement; eventually leaving the downstairs panel with only the feed coming in and then going out to the upstairs box.

From the upstairs box I could run new circuits up the the attic and then down to each room as I remodel (if going through attic is ok with code).

My questions:

Is this plan alright for code?

What size/type of wire should I use to feed the 100A sub panel?

Should this feed be run in the interior wall cavity or back outside and then back inside upstairs?

Is there a "more correct" way to keep the current circuits supplied and install a new panel upstairs that I can use for wiring new circuits?

Thanks in advance.


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Ron Natalie

This is fine. You will need to run cable (or conductors in conduit) of the appropriate ampacity. This will need to be on the order of #2 wire, but it will vary depending on the type of wire used. You will need to run two hots, a neutral, and a separate ground. The upstairs sub panel will need to have the grounds and neutrals separated (how this is done depends on the manufacturer of the panel).

How you want to run it is up to you. I'd be reticent to run things outside the house but it is technically legal as long as the wiring method used is approved for such.

    Bookmark   December 23, 2011 at 12:01PM
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Before you start anything, really need to check with the local authorities to see if you are legally allowed to do this work. Your post says that it is "2 units" and in most areas the owner is not legally allowed to do electrical work in rental units.

    Bookmark   December 27, 2011 at 9:25AM
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Thanks, seems like I'm on the rigth track then. The house is owner occupied so I don't think that is a problem. I occupy the upstairs and my brother the down stairs (we both own it).

    Bookmark   December 27, 2011 at 6:13PM
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Ron Natalie

Multiunit buildings regardless of who owns what units are generally NOT subject to the exemptions to allow homeowners to do their own wiring.

    Bookmark   December 28, 2011 at 12:25PM
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You should definitely consult your local authority about what type of work you are allowed to do in your situation and you definitely need a permit.

Beyond that, if you are doing a major rewire, you should look forward a bit. 100 amp service for a multifamily dwelling is way below modern standards and you should look at upgrading that. Also, if the building really is 2 units, you should consider wiring them as such. eg each unit on separate panel that they can access. You might not plan on them being rentals now but plans can change or you might want to sell.

    Bookmark   December 28, 2011 at 1:26PM
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I will look into the laws regarding if I can do the work myself. However, to clarify, both units DO have separate meters and panels. All of the work I am talking about doing involves only the 100A panel that is for the second floor. The first floor has a 150A main breaker in the basement and my brother plans on keeping it and rewiring each circuit as we remodel.

Thanks for all the info.

    Bookmark   January 2, 2012 at 12:15AM
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