Mixing different gauges of wire in a circuit


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Old 01-31-04, 12:43 PM
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Question Mixing different gauges of wire in a circuit

I had an licensed electrian upgrade the service to my house from 60 Amp with fuses to 100 Amp with circuit breakers. In doing so he mounted the new circuit breaker box next to the fuse box and essentially turned the old fuse box into a big junction box. For 15 Amp circuits he ran NM-B 14/2 AWG from the circuit breaker to the old fuse box and connected them to the original house wiring (50 yrs. old).

I want to replace those original wiring with new wires. Can I connect 12 AWG wiring to 14 AWG wiring on a 15 Amp circuit? From an electrical standpoint I understand that this isn't dangerous, but from a "best practices" standpoint, is this something that is not a good practice?

There are 2 reasons why I am using 12 AWG: 1) I had read somewhere that even though 14 AWG is minimum for 15 Amp circuit, that 12 AWG would be even better; 2) I will also be rewiring and adding some 20 Amp circuits and would rather just purchase bulk amount of one size of wire.

If I shouldn't connect the 12 AWG to 14 AWG, would it better to replace the 14 AWG with 12 AWG or should I just use 14 AWG on the 15 Amp circuits?
 
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Old 01-31-04, 12:57 PM
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Although not everyone would recommend it, there is no code that prohibits using 12-gauge wire on a 15-amp circuit. If you use all 12-gauge wire from the junction box on, it will be fairly easy to upgrade the circuit to a 20-amp circuit later.

The assertion that 12-gauge is "better" and 14-gauge has some validity, but is a weak argument.

The desire to just mess with one kind of wire is a fair argument.

Go for it!
 
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Old 01-31-04, 01:17 PM
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To me the point about only wanting to buy bulk of one size wire is your only valid one.
No, 12 is not better than 14. While 14 wire is only allowed to be put on a 15 amp breaker, do you know the actual ampacity of it? 20 amps. The code prohibits it's use on a 20 amp breaker but my point is 12 is NO safer or better.
It is bad practice to mix wire sizes IMO. If you need a 20 amp circuit, run 12 wire. If you need or want a 15 amp, run 14 wire.
 
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Old 01-31-04, 06:12 PM
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Personally, I run #14 on 15 amp circuits. The heavier 12ga wire is much stiffer and more difficult to work with. Run #12 if you need it, but it's a pain in the a$$ if you don't. Also, most residential outlets & switches are designed to work with #14. The "push in" connection holes on the back of the switches and outlets are sized for #14 and will not accept the larger #12 wire.
 
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Old 01-31-04, 07:06 PM
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Originally posted by Pilot Dane
..... The "push in" connection holes on the back of the switches and outlets are sized for #14 and will not accept the larger #12 wire.
Yes that is true, but a much better connection can be made by wrapping the wires around the side screws which will accept either # 12 or # 14 wire.
 
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Old 01-31-04, 07:36 PM
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Yes, nothing beats a good screw...
 
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Old 01-31-04, 07:36 PM
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Hotarc makes a very valid point.
Backstab connections are strongly discouraged by most seasoned electricians.
 
 

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