Can I run a 12-3 wire from a 14-2 wire (15amp breaker)?

15 years ago

Want to install a 3 way dimmer. Existing switch is powered from a 14-2 wire. I have 12-3 wire that I can run to the new dimmer switch. Is it OK to use 12-3 for this or do I have to use 14-3? all circuits are on a 15 amp breaker.

thanks.

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Comments (6)

wayne440
15 years ago
The 12-3 should be OK.
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bigbird_1
15 years ago
You can use any NM or even AC90 or THHN/THWN wire that is 14 ga or thicker. The 15A breaker demands a minimum of 14 ga but there is nothing wrong code wise with going with a thicker wire except for convenience of working with it and the price. In the future if someone saw 12 ga wire they might assume a 20A breaker. It's not best practice to mix wire sizes on a cc't, but it is code compliant.
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It is always ok to use bigger wire, which is indicated by a smaller guage number (isn't the world logical?). I.e., the #14 extension cord is bigger than #16 and so is more capable of carrying the current drawn by a load. The load (microwave) basically draws as much as it needs regardless of the wire, and too small a wire size would overheat. The circuit breaker should trip if the load tries to draw too much. Manufacturers are allowed to use #16 when they design and test equipment to make sure it is safe, so it is ok if they installed #16 coming out of the microwave The smallest wire allowed to be put in house walls is #14, in order to avoid overheating with maximum loads on a 15 amp circuit breaker. It is a good idea to use heavy extension cords when they are needed for temporary situations. Code prohibits "permanent" use of extension cords in place of fixed wiring.
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all the lights in my house are on 12/2, heck there ain't a 15 amp breaker anywhere in teh panel. but i promise you i WISH there was at times! week before last i decided to put up secutiry lights since we were going out of town and the lady house sitting for us did not like how dark it was around the house(plus my wife has been asking me to do it for 3+ years). anyway i decide to put the switch right next to the back porch light switch and use that circuit to feed the lights. well, turns out that the reason they used 12/2 is that 1/3 of the lights are on 1 20A ciruit, 1/3 on another, and roughly 1/3 on another. only the bathrooms have dedicated lights! the way teh panel is in the wall will require that i rip open the sheetrock to pull new feeds, so that will be saved for later this summer when we redo the cabinets in there anyway. back to my point, 12/2 is great in that you can have more load per circuit, but i really sucks when you are trying to stuff three 12/2 feeds back in a box behind 2 switches! and yes, i use the largest box i can for ease of use and wirefill.
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Brickeyee is right thats how my last house was wired, dw and gd on a 20 amp together but mine were not cord plugged. putting both on separate breakers is overkill but can do no harm. if you were using 12/3 and two breakers the neutral is shared by both circuits. normally neutral is not connected to a single pole switch which would control the GD it will continue on to the recptical. since you are going to be splitting it so half is switched the neutral is shared and has to connect to both halves. I think you could just not break the tab on the side your white wires connect. the black will go to the switch and then to the GD's outlet (top gold screw with separation tab broken off on the hot side) The red wire would go to be in to the switch's box in the wall and just be spliced to the same going out to the bottom outlet's gold screw for the DW. red would not be connected to the switch it would just be spliced with wire nuts and placed behind the switch in the box. be sure you ground everything as required.
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bppark
15 years ago
Most professionals would consider it unprofessional, but if you already have the cable, there's no technical or safety reason why you can't use it, as long as the whole circuit stays on a 15-amp breaker. The only danger with this sort of thing is that some clueless person might come along later to make modifications, get confused, and do something stupid.
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perel
15 years ago
If you do use 12ga wire, it's good practice (and courteous to the next person working on that circuit) to put a clear note in the box and on the wire "14GA UPSTREAM IN CIRCUIT" or something along those lines so they'll know that the 15A breaker is there for a reason..
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billhart
15 years ago
I would call that DOWNSTREAM, but wholeheartedly endorse the idea of attaching a label to the wire.
0
bigbird_1
15 years ago
Perel wants to put the note in the device box, not the panel, so there is indeed 14ga cable upstream of the device box.
0

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Can I run a 12-3 wire from a 14-2 wire (15amp breaker)?

Comments (6)

wayne440

bigbird_1

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