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Refeed existing sub panel

Posted by fotostat (My Page) on
Thu, Nov 12, 09 at 22:21

I have a sub panel in my attic that feeds the upstairs lights and receptacles. That sub panel is fed with a piece of 10-2 BX. They used a jumper to make the other bus hot (there are no 240V loads up there, so it works fine). Is that in any way legal?

I'd like to refeed it, my plan was to change out the 30A single pole breaker with a 40A two pole breaker and run a piece of 8-3 romex up there, should be pretty straight forward.

40 amps should be more than enough since 30 amps has been fine and there is no possibility to expand the upstairs or anything like that. The AC unit in the attic is fed from the main panel.

My questions, is 40A too much?

Is using romex the best option, or should I use a different type of cable for some reason?

Follow-Up Postings:

RE: Refeed existing sub panel

I'm not a code expert, but I see nothing wrong with feeding both panel busses from a single hot leg. You would not have to replace the 30A breaker.

If you have been getting along with 30 A single hot leg, then 40A with two hot legs is as much total power as 80A from a single leg and considerable overkill.

You should be just fine with either 30A or 40A at 120V. You could also use 20A 120/240V on 12-3 which increases your total capacity, unless there is some 120V load that needs more than 20A by itself.

RE: Refeed existing sub panel


The power to your subpanel is limited by the breaker in the feeding panel, which in this case would be a single pole 40A circuit. Feeding that wire to both legs of the subpanel wouldn't provide any additional power, but I suppose would give you additional slots for breakers. Regardless of code violations, I wouldn't do it because if someone installed a double pole breaker for use in a multiwire circuit, it would overload the neutral. Very dangerous.

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