12 awg wire 40 amp breaker - ECN Electrical Forums

I bought a new house with a garage that is wired using 12-2 awg wire on a 40 amp breaker. Is that right? What is the max amps 12-2 wire can handle? Thanks!

No, unless it is a branch circuit feeding an A/C unit or a motor. 12-2 NMB ampacity is 20 Amps.

Hi, the 12-2 on 40 amp breaker is what is powering my whole garage. So you say this is wrong?

If you in fact have 12-2 Type NM cable supplying a general purpose (lights and receptacles) branch circuit connected to a 40Amp circuit breaker then you have a NEC violation as well as a potentially dangerous situation. You say this is a new home. I would contact the builder and ask him to have an electrician inspect this. Maybe also contact the local electrical inspectors office. It should not have passed inspection.

I bought the house this year, had it inspected but the wiring to the garage wasn't caught. I'm calling an Electrian today. From what I read I need about an Awg wire.

What you need is a 20 amp breaker protecting the existing circuit, assuming that no factors exist in your house which would force derating of the circuit to 15 amps. If you need more than a single 20-amp circuit in the garage, discuss that with the electrician and (s)he can look at what the cost would be to install additional circuits.

You might also consider having the electrician do a safety check on the garage and your wiring installation. Are the receptacles in the garage GFCI-protected? Are there other safety issues that were missed in the earlier inspection?

I have 4 lights plus 8 15 amp plugs and yes one gfci running on the 12-2 wire. Would it be enough to simply change the breaker to a 20amp. Or will the 20 amp on 12-2 still be overloaded? Thanks for taking your time to answer!

Ok I just took a look at my breaker box. I have a double pole 20 amp breaker on the 12-2awg wire. Is my garage safe?

Jane,

12 gauge wire is properly protected by a 20 amp breaker. More than that we cannot tell from here. If you really do have 12-2 wire and a 2 pole breaker there may be a problem.

Please have an Electrician look closely at your situation to be sure.

[This message has been edited by Webmaster (edited 05-11-2004).]