mixed wire guage

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  #1  
Old 01-08-06, 09:17 AM
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mixed wire guage

Can I run #12 wire from a single pole 15amp breaker and connect the #12 wire to #14 wire in a junction box? I was told that this is ok but not sure. i know you can use #12 wire on a 15 amp breaker and it is evcen code some places, but not sure if you can connect #12 to #14.
 
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  #2  
Old 01-08-06, 09:25 AM
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14 AWG may carry a maximum of 20 Amps in free air, or 15 Amps as part of a 3 conductor cable. 12 AWG may carry a maximum of 25 Amps in free air, or 20 Amps as part of a 3 conductor cable. So long as what you are wiring in will not pull more amps than what a 14 AWG can handle there will be no problem.
 
  #3  
Old 01-08-06, 10:11 AM
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Bloodstone's post could be misleading. #12 can never be protected by more than a 20-amp breaker, and #14 can never be protected by more than a 15-amp breaker. The discussion of the ampacity of the wire in free air is meaningless, because, even in free air, you can't use larger than these breaker sizes. This is an example of the misinterpretations you can make by getting information from just one section of the code. The code must be taken as a whole (all 750 pages). For these reasons, it is usually recommended that DIYers not try to get their information from the NEC, unless you are willing to study all 750 pages.

None of the above has anything to do with the original question, but I felt compelled to respond to potentially misleading information.

... Now, back to the original question.

The answer is that "yes", you can do it, but "no", you should not do it. Although code allows #12 wire to be used on a 15-amp circuit, it is bad form because it could fool some person into believing that it would be safe to change the breaker to a 20-amp breaker. And even though the code allows it, some inspectors may reject it as bad workmanship.

In rare instances, you might need a larger wire size than the breaker requires, usually because the run is very long (say, significantly longer than 150 feet). In this case, you should be sure to note this situation in the panel where it will be obvious to anyone who looks at in the future.
 
  #4  
Old 01-08-06, 10:47 AM
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John's right - you can do this, but don't. I wasted most of an afternoon and made more than a dozen trips in an out of a crawlspace once because of the confusion 12 ga wire on a 15 amp circuit can cause.
 
  #5  
Old 01-09-06, 09:45 AM
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[QUOTE=John Nelson]

The answer is that "yes", you can do it, but "no", you should not do it. Although code allows #12 wire to be used on a 15-amp circuit, it is bad form because it could fool some person into believing that it would be safe to change the breaker to a 20-amp breaker. And even though the code allows it, some inspectors may reject it as bad workmanship.
QUOTE]

Is there anything wrong with using #12 wire on a 15-amp circuit if the entire wire is #12?
 
  #6  
Old 01-09-06, 09:51 AM
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Originally Posted by Tyger52
Is there anything wrong with using #12 wire on a 15-amp circuit if the entire wire is #12?
With the exception of voltage drop or aluminum wiring, why would you do this?
 
  #7  
Old 01-09-06, 09:09 PM
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Cauldwell's advice

Originally Posted by racraft
With the exception of voltage drop or aluminum wiring, why would you do this?
In Rex Cauldwell's book, somewhere, he says he would rather have all #12, even to lights or other circuits that can safely use #14. In fact, that has been stated on this forum, but I am not sure who wrote it. I am just trying to go above code. The only reason I would use the 15 amp breaker is that I already have a few of them and it seems like a waste to not use them. On the other hand, I might mark my panel with a note that all wiring is #12 to avoid the confusion of someone besides myself doing work on the system.
 
  #8  
Old 01-09-06, 09:24 PM
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If you use all #12 on a circuit, then just use a 20-amp breaker. The cost of 20-amp breakers is exactly the same as the cost of 15-amp breakers. Save your extra 15-amp breakers for some other application.

Note that using #12 on a 15-amp circuit increases the work in pulling the wire. You may not care about this. But it also increases the crowding in the boxes.

But if you still really want to use 15-amp breakers on a circuit with all #12 wire, you certainly can.
 
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