12 gauge wire on 15 amp circuit?

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  #1  
Old 10-26-05, 02:24 PM
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12 gauge wire on 15 amp circuit?

I know that it is unacceptable to have 14 wire on a 20 amp circuit, but I noticed that someone who worked on my house at some point in the past had run 12 gauge stranded THHN/TWHN in a conduit in the cellar as part of a 15 amp circuit.

My sense is that there is no problem with this (in that the 15 amp breaker would trip long before a 12 gauge wire was in any jeopardy) and that this is perhaps an odd case of overkill.

But, just in case:

1. Is there any reason anyone can think as to why this 12 wire is situated in a 15 amp circuit (the rest of which is all 14/2).

2. Is there any problem/danger associated with using 12 on a 15 amp circuit?

Thanks in advance
 
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  #2  
Old 10-26-05, 02:32 PM
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The only danger of 12-gauge wire on a 15-amp circuit is one of possible future confusion. There is no current danger.

So why would somebody put #12 on a 15-amp circuit?
  • They happened to have some #12 lying around and no #14.
  • The run was really long and they were trying to reduce voltage drop.
  • They wanted to allow for an upgrade to a 20-amp breaker later (although most people would say that if this case applies to you, just put in the 20-amp breaker to begin with).
  • They like to overengineer things.
 
  #3  
Old 10-26-05, 03:09 PM
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There is nothing 'wrong' with using 12 ga on a 15 amp circuit, but it makes for some confusion when trying to find the breaker if you assume that 12 ga means it's a 20 amp circuit. I went in and out of a crawlspace more than a dozen times at my in-laws' lake place because of this.
 
  #4  
Old 10-26-05, 09:00 PM
Whitey55
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Nothing wrong at all. I have this in my house. I found out that the "homerun" to the breaker was 12awg but additional devices on the same circuit had 14awg on them, so don't assume you could change it in the future without knowing what is all on that circuit.
 
  #5  
Old 11-01-05, 09:55 AM
coffeebrk
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12ga. on 15amp circuit...with 15a-125v outlet

Hello,

This thread was useful to me also. I have a similar situation with a 15 amp circuit and 12ga. wire used to wire recessed lights and outlets, but I wanted to add an additional 15 amp outlet that specifies use 14ga. wire only.

Should I worry that the other outlets need to be converted to 14ga. wire?

Thanks for the help.
 
  #6  
Old 11-01-05, 10:12 AM
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If you have a 20 amp receptacle on a 15 amp breaker then you have a issue that needs to be corrected. You need to address this issue without regard to whether or not you add anything to this circuit.

If you truly have all 12 gage copper wire (each and every piece), I would suggest that you stick with 12 gage wire regardless of what you are adding to the circuit. Go ahead and use a 15 amp receptacle if you want (assuming you aren't in Canada), but go with 12 gage wire.
 
  #7  
Old 11-01-05, 10:22 AM
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15 amp outlet that specifies use 14ga. wire only
That's unusual. Can you provide more details? I hope you're not talking about backstab connectors, which you shouldn't be using anyway.
 
  #8  
Old 11-01-05, 12:56 PM
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Via PM:
Hi John,

Thanks for the reply. The outlet I am using is a Leviton 2-pole, 3 wire grounding Duplex Outlet, side wire screws and Quickwire (straight into the back).

The circuit is on a 15 amp breaker but the wiring is 12/2 solid w/ground wire. I just noticed that the Leviton outlet instructions read "use 14ga. wire only" for Quickwire connection. For 20 amp circuits use side wire screws.

So is it OK to continue using 12/2 wire in the 15amp circuit and connect to the outlet via the side wire screws?

Thanks.
Yes. Never use the quickwire connections. Always use the screws.
 
  #9  
Old 11-01-05, 01:14 PM
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The reason that we suggest not using the quick wire or back stab connectors is because they have a tendency to fail. Yes, they work for a while, sometimes for a long, long time, but other times, especially under load they just fail. Many a homeowner has had to spend time tracking down an "open hot" or "open neutral", only to find that the culprit is a failed back stab connection.

Yes, it takes a little longer to bend the wire to go around the screw and to tighten the screw, but you will realize just how much time you have saved when you have to spend time even once finding and fixing an open connection.
 
  #10  
Old 11-04-05, 02:09 AM
MKISSEL
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Lightbulb

ALWAYS USE THE SIDE SCREW CONNECTION AND BY CODE WRAP THE WIRE CLOCKWISE AROUND THE SCREWS, SO THAT WHEN YOU TIGHTEN THE SCREW THE WIRES WILL TIGHTEN WITH IT. I'VE SEEN ALOT OF COUNTER CLOCKWISE CONNECTIONS AND IT JUST BOTHERS ME, CAUSE THEY CAN COME LOOSE.
 
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