amp vs awg


Old 05-14-04, 08:51 AM
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amp vs awg

Am I able to use 12 awg wire on a 15 amp breaker. I know it will work but is it ok by code and if so where can I find that info. thanks
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Old 05-14-04, 09:23 AM
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
Yes, you can use 12 gauge wire on a 15 amp breaker. In fact, there are certain situations where this is necessary to get the appropriate voltage at the destination. If so, I recommend 12 gauge wire for the entire circuit, rather than mixing 12 gauge and 14 gauge on the same circuit.

The problem with using 12 gauge wire on a 15 amp circuit is that someone may make an incorrect assumption later on and either change the breaker to 20 amp, or try to draw 15 amps or more through the circuit.
Old 05-14-04, 08:16 PM
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Another problem that I encountered with 12 guage is that it's much harder to work with than 14 guage. Especially if you are using EMT conduit.

I began using 12 guage in a basement remodel because I began with a 20 amp bathroom circuit and a 20 amp circuit for a workshop.

From pulling, to negotiating inside 90's, to connecting to fixtures(switches, receptacles, etc) was difficult.

I then used 14 guage on the 15 amp circuits (voltage drop was not a problem),and my life became much easier.

My reply is based upon using individual reels of THNN.
Old 05-19-04, 09:08 AM
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Using 12GA wire

In residential, I always like to use 12ga wire because then you always have the capicity to increase the load safely. If you were buying, lets say a boat, and a 20 footer cost a couple more dollars more than than 16 footer what would you choose? Now if you are wiring a hotel and you need a couple millon feet of wire that would be a different story. I don't see much of a price break between 14ga and 12ga wire and 15amp circuit breakers and 20amp circuit breakers that it makes any sense to run 15 amp circuits. As for wirenut 3/4 conduit is as easy to run as 1/2 conduit. By code you can only put so many conductors in a conduit before derating anyway.
Happy wiring and be safe.
Old 05-19-04, 09:22 AM
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reply to racraft

12 ga wire is rated for 20 amp load (NEC 1999) So you should not worry if someone would exchange a 15 amp breaker for a 20. I suggest no one ever do that unless they are 100 percent sure of all down stream wiring conditions.
Old 05-19-04, 07:25 PM
Join Date: Apr 2003
Location: Eastern PA
Posts: 354
two comments on this.
One: I tried to run 12 ga where I could but in a 100 year old house the real problem became getting a box in the wall big enough to meet BOX FILL requirements. So I ended up with a lot of 14 ga. circuits where I had hoped for 12 ga.

Two: I completely agree that running 12 ga. wherever possible makes for good common sense but that does not mean you should protect the circuit at 20 amps. If you have a dedicated circuit for lighting, computer, fridge or whatever that you know is never going to use more than six or seven amps then protect the circuit at 10 or 15 amps. The only thing you have done by using the 20 amp breaker on that type of circuit is increase your chances of really blowing the top of something if there is a problem.
If you need more current at a later time then you can pop in a 20 amp breaker with no rewiring required.
Old 05-20-04, 05:46 AM
Join Date: Sep 2003
Location: Central New York State
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You do not understand my point. I am well aware of the current capacity of wires. My concern is in mixing 12 and 14 gauge wires on a single circuit.

If someone wires an entire circuit with 12 gauge wire but uses a 15 amp breaker, it would be okay in the future to swap in the 20 amp breaker. However, if someone mixes 12 and 14 gauge wire on the same circuit, someone later on may not look at the entire circuit. They may see 12 gauge wire at the panel and assume that the whole circuit is 12 gauge, and simply replace the 15 amp breaker with a 20 amp on, whoich would be a real problem if part of the circuit was 14 gauge wireing.

I thought I could get away without stating the above. Obviously I couldn't. Next time I will be more explicit in my posts.

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