Wiring outbuilding

[HorneTD]

Bob nailed it so see his answer.

-- Tom Horne

[Bob Vaughan]

IIRC, the minimum size for feeders is 30A, which means that the #12 cable is undersized, and the installation cannot meet code with the subpanel in place.

You need to either remove the subpanel, and turn this into a multiwire branch circuit, or replace the feeder cable with a minimum of 10/3 UF. Given the distance involved, I would use at least #8 to compensate for voltage drop, if not #6.

[HorneTD]

You did say you were working from memory but I would be interested to know what national code language sets a minimum size for a feeder. If it is a local amendment or code I'm not interested.

-- Tom Horne

[zxcvbob]

215-2(a)

Feeders smaller than 30A might not make any sense, but I can't think of anything inherently unsafe about them, so this might be one of those cases where the NEC has a solution in search of a problem. I wouldn't dig up a buried cable just to satisfy this part of the code unless an inspector told me I had to. (I might dig it up because I realized too late that 20A wasn't big enough, or because the voltage drop is unacceptable, but not just to satisfy this point in the code.)

Bob

[HorneTD]

You're right! There it is in 215-2(a)(2) in plain black and white. I really appreciate your taking the time to find that reference. I was obviously unfamiliar with it. Now there is absolutely no good reason that the OP would want to keep that panel in the out building. If he combines both circuits in the out building into one branch circuit he could then supply it with the twelve gage two wire feeder but what would be the point of that. His best course of action is to remove the panel from the out building and substitute a large J box with a switch mounted in a raised cover to function as the building disconnecting means. That switch should be rated for the entire ampacity of the twenty ampere circuit. At least then he will not be obliged to install a grounding electrode system.

-- Tom Horne