My son hired an electrician (freelance) to add outlets in his living room. One of the outlets was to be a dedicated service to an (10k btu) a/c unit. I provided him with 250’ of 12/2 Romex. The wire run was less than 40’in the basement and to the panel box. When the guy finished he had 12/2 connected to a 20amp breaker to a junction box (just below where the proposed outlet is in the basement) where he changed the wire to 10/2 fed it out the basement wall sil-plate, under the covered porch and fed (About 20”) it back into the house on the 1st floor.(my guess is that it would be difficult to fish the wire through the floor/wall) I am not an electrician but I was under the assumption that the breaker amp should fit the wire. Any thoughts on why he changed the wire gauge? Are there restrictions about wire running outside? Should the breaker be 30 amp?

1 Answer 1


Probably had 10/2 UF (needed to go outside - gray insulation jacket) on the truck. NM/B (Romex) can't go outside or in any wet location.

Breaker needs to protect the SMALLEST wire in the circuit. Larger wire is always fine. Since there is 12Ga in the circuit, 20A is the maximum breaker size.

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    And I looked up a 10k btu a/c at random - ~ 8 amps - so a 15 or 20 circuit is appropriate. Commented Jul 7, 2021 at 1:46

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