# Can you use 12 gauge wire on a 15 amp breaker?



## ponch37300 (Nov 27, 2007)

I'm doing some work in my basement and ran into something I wasn't sure of. The basement was finished and I'm just adding a couple lights and outlets. When it was wired they used 12 gauge wire from the switch to the can lights. When I located the breaker for this circuit it is a 15 amp breaker. I'm not sure why they used 12 gauge on a 15 amp breaker but have a couple questions.

First question is this alright to have 12 gauge wire on a 15 amp breaker instead of 14 gauge? Second, do I have to use 12 gauge wire if I want to add one more can light? Or can I use 14 gauge wire to go from an existing can light(currently wired with 12 gauge) to the new can light? Or is it a no no to mix wire gauges like this?


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## Jim Port (Sep 21, 2007)

The #12 is fine on a 15 amp breaker.

The #14 can be used on a 15 amp breaker. Some consider it confusing with mixed wire sizes.


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## AllanJ (Nov 24, 2007)

If all of the wiring (including branching off in different directions) for that circuit is #12 then you may upgrade the breaker to 20 amps. Adding onto the circuit using #14 wire erases (extinguishes) the chance of upgrading the breaker unless there was already some #14 wire on the circuit precluding the use of the larger amperage breaker.

For a long run, say, from the house to a backyard shed, a larger size (such as #12 instead of #14) may be needed to reduce voltage drop even if there are thinner (say, #14) wires in other shorter sub-branches of the same (say, 15 amp) circuit. 

Although it is suggested that the breaker reflect the usable capacity of the circuit, length, allowable voltage drop, and all, the only requirement is that the breaker size go with the wire size and, if applicable, maximum ampere ratings of wired-in (hard wired) appliances and receptacles.

Unlike with plumbing, the benefit of a thicker wire running the bulk of the distance (say, out to the shed) is not lost if the first several feet (from the panel ) is of a thinner wire. The more thicker wire in the aggregate along the long run, the less the voltage drop, all other things being equal.


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## dalepres (Mar 20, 2011)

I'm not a pro at all but I either wire with all 12 gauge everywhere or I maintain strict adherence to 12 gauge in 20 amp circuits and 14 gauge in 15 amp circuits. 

You don't ever want to assume that a circuit is a 20 amp circuit just because because you find 12 gauge wire, though.


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