Can I add 14-3 to a 12ga branch circuit


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Old 03-14-04, 08:23 PM
rdswartz
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Question Can I add 14-3 to a 12ga branch circuit

I am remodeling a master bedroom and re-wiring the entire room. I have used 12-2 for a dedicated circuit for a room A/C (until C/A is added) and used 12-3 for receptacle outlets on another circuit (3 switched and 2 unswitched). I wanted to have another branch in the box with the switched outlets for a ceiling fan and light and was wondering if this could be done in 14-3, powered from the receptacle circuit that has 12-3 cable. If I use 14-3 for the ceiling fan/light, does the entire branch circuit need to be 15amp? Does this meet NEC if I limit the circuit to 15 amp? I realize the possibility of confusion and potential for someone to later replace the breaker with a 20 amp OPD. It does seem somewhat ridiculous to have to run this last leg of the circuit in 12 ga since I will be connecting to 16 ga wire in the fan/light fixture. It is unlikely someone is going to add onto the ceiling box with a continuation of the circuit later. I do not want to have a lengthy discussion with the electrical inspector, and I realize the simplicity of just running everything in 12 ga, but sometimes the route can be a little tight and 14 ga is still easier to pull through a tight spot! Thanks for your help and suggstions!
 
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Old 03-14-04, 08:56 PM
J
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Most people do not recommend mixing wire sizes, but it is not a code violation to do so. You must, however, protect the circuit for the smallest wire on the circuit. So it there is any 14-gauge wire, the breaker must be 15 amps.

Since you don't want a lengthy discussion, I won't give you one. Use 12-gauge wire.
 
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Old 03-14-04, 08:58 PM
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I think you know the answer already. Do you want soemone to tell you "Aw, go ahead" to make you feel better?

The real answer is don't do it.
Unless you change the breaker and make a note on the wire why the non-standard breaker is installed.
Really there is no reason to change wire sizes in the middle of a branch circuit.
 
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Old 03-14-04, 09:19 PM
W
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As you may have noted, the wires on the fixture itself are much smaller than the 12 ga wire that feeds the fixture.

There are rules for so called 'tap conductors'. These are conductors which are large enough to carry current for the load served, but smaller than the current rating of the overcurrent protection. Basically a tap conductor is 'protected' from overload by having a fixed load served, and the circuit breaker only provides short circuit protection. Because tap conductors are not protected from overload by the circuit breaker, there are strict restrictions on the length of the tap conductors and how they may be used.

For example fixture wires are permitted _inside_ the fixture, where the fixture itself could contain combustion in the event of overload. The fixture wires have an amp capability sufficient for the lamp, but not sufficient for the full circuit current.

For residential applications, the difficulty of figuring out how to use the tap rules, and the extremely limited utility (very short lengths) basically mean that you simply don't use taps. Use 12ga for 20A circuits and 14ga for 15A circuits, and don't worry if you could actually get be to code if you used 14ga in the last couple of inches of the circuit.

-Jon
 
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Old 03-15-04, 02:35 PM
rdswartz
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Thanks for your help! I think I'll play it safe and just change the fan/light circuit to 12-3 that way there is no danger if the breaker gets changed to 20 amp for some reason. I really appreciate the response. This is a great service to DIY's.

I realize many who try or think they can DIY are in over their head and while it is one thing to fix a leaky pipe because you didn't know how to solder a joint, DIY wiring can have more serious implications. In some parts of the country though, it is difficult to hire a professional that is dependable and at a reasonable cost. In northern NJ, there are many outstanding contractors and most are very, very busy. The better ones are next to impossible to get and difficult to schedule if you are lucky enough. That leaves open the opportunity for others who are not so reputable. That creates a need for DIY to undertake many aspects of home remodeling and I want to thank you guys for helping us do the job right!

Darin Swartz
 
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Old 03-16-04, 08:07 AM
W
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I noticed an error in my comment above. I wrote it on the assumption that the '12ga circuit' was protected at 20A. In this case the use of wires smaller than 12ga is limited by very strict and somewhat confusing rules, and it is better (IMHO) to simply use 12ga wire for the entire circuit. I just sort of went off on the fact that one _can_ do this in _very_ limited circumstances.

The general rule is that the entire circuit needs to be protected for the smallest wire in the circuit, (with exceptions...if you are interested, then buy a copy of the NEC). There is no specific rule preventing you from using _larger_ wire than required. This means that if you mix 12ga wire and 14ga wire, and then you protect with a 15A breaker, then you are code compliant. Mixing wire gauge can be confusing, and that is why people are recommending against it. But if a situation comes up where it actually seems the right way to go, then it is code compliant.

One situation where it is appropriate to use larger wire mixed with smaller wire is an extremely long 'home run' where voltage drop could be an issue. In this case, you would use the larger wire for the bulk of the run between the circuit breaker and the first junction box, and then switch to smaller wire. While it might be less confusing to simply used the same size wire for the entire circuit, larger wire is harder to work with and takes up more space in boxes, can be difficult to attach to devices, etc. For example, you may find with a circuit that goes a long way from the box that you need to use 10ga wire to get acceptable voltage drop. But working with 10ga wire is a pain, and if the circuit is protected at 15A, then it probably makes sense to use 10ga wire for the long run, but then 14ga wire for all of the connections at the locating being served. If you do this, it probably pays to make a note of this on the circuit directory.

-Jon
 
 

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