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Mixing 12-ga and 14-ga wire?

CVBReno | Posted in Construction Techniques on October 10, 2006 08:03am

A question for you Sparkies…

I’m re-wiring about 1/3 of my house for a major remodel.  I am finding that the existing 20-amp outlet circuits use 12-2 wires as they should, but on several of these circuits there are lighting circuits branching off (ahead of the outlets).  The 12-2 hot line from the main breaker box goes into a switch box to power a light circuit, and ties into another 12-2 line going back out to the plugs — but the wiring for the light circuit branch is usually 14-2 (or 14-3 for three-way switches). 

These light circuit branches are not pulling more than 15 amps, and there are no “downstream” plugs on the same branches, just lights.  From a technical standpoint it doesn’t seem like it would be a safety hazard to do this, but I read that it’s not recommended to mix lighting and outlet circuits in this way.  And is this mixing of wire sizes OK by the code?  If not, is it likely that the building inspector will make me re-wire the whole house, or just the circuits involved in the remodel?

Thanks for your help!

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Replies

  1. User avater
    BillHartmann | Oct 10, 2006 08:19pm | #1

    "but I read that it's not recommended to mix lighting and outlet circuits in this way."

    With minor exception there is no code against having lighting and receptacles on the same circuit. The exceptions are the kitchen small appliacne circuits and the the bathroom circuit if it feeds more than one bathroom

    One reason for keeping them separate is that if you overload and pop a breaker then you lose will be in the dark. But if you have a reasonable number of circuits and have updated the circuits that is rare.

    Another advantage is that you can work on the receptacles in a room and still have lights. Or work on the lights and still have receptacles for lighting. But you can run an extension cord from another room when you need to do that.

    "And is this mixing of wire sizes OK by the code? If not, is it likely that the building inspector will make me re-wire the whole house, or just the circuits involved in the remodel?"

    Just the circuit envolved. Or you can downgrade the circuits (except a bathroom) and replace the breaker with a 15 amp one.

    If you do the dowmgrade I would point out the inspector what you did rather than him finding the different wiring on one circuit and them questioning everything until he finds out (if he does) that it is on a 15 amp circuit.

  2. User avater
    Soultrain | Oct 10, 2006 09:04pm | #2

    I've wondered about that before, but the problem comes in if there is a short or something.  Suppose it's not a dead short, but causes a draw > 15A.  In your scenario, it would be trouble since the breaker is 20.

    Mixing 12 & 14 wouldn't be an issue as long as the breaker was used for the wiring with the lowest Amp rating - then again, you could still run into problems down the line if someone decides to up the breaker after noticing the #12, but not the #14

    1. CVBReno | Oct 10, 2006 09:35pm | #3

      Good point about the "partial short" drawing between 15 and 20A.

      Sounds like I should use 12-ga wire for any new lighting branches on circuits like this wherever I can, and replace the 20-amp breakers with 15-amps on the others when I find them.

      I'm finding a lot of not-totally-kosher stuff in this house, both plumbing and electrical.  For example, I found a three-gang light switch that was relocated by about 2 feet, apparently before the drywall was installed.  There were nine cables spliced with twist-on wire ties inside the wall, not even taped.  It might have happened after the inspection but before the drywall, I don't know.  That one is all fixed now.

      More joys of remodeling!

      1. DanH | Oct 10, 2006 10:53pm | #5

        > That one is all fixed now.You taped them up? (VBG)

        If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison

        1. CVBReno | Oct 10, 2006 11:14pm | #6

          Taped them up?  Gee, that would have been a whole lot easier! ;-)

          I got rid of the "extensions" (a total of 35 wire nuts in the wall space) and temporarily re-attached the box, but at the moment it's all hanging loose from the ceiling because I removed the wall it was in.  I have to  move the switches to other locations and re-wire that whole room, but keep the lights functional in the meantime.  

          Sometimes this whole experience of remodeling while living in the house seems like overhauling a car engine while driving!

           

          1. DanH | Oct 10, 2006 11:41pm | #7

            More like changing the tire.
            If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison

          2. BryanSayer | Oct 10, 2006 11:59pm | #8

            All four tires. Blindfolded. Simultaneously. With one hand tied behind your back.

          3. DonK | Oct 11, 2006 12:47am | #9

            Sometimes this whole experience of remodeling while living in the house seems like overhauling a car engine while driving!

            I love that analogy!!!

            Don K.

            EJG Homes     Renovations - New Construction - Rentals

  3. DanH | Oct 10, 2006 10:51pm | #4

    No one's been able to identify a general restriction against mixing wire sizes on a circuit, but some inspectors may not allow it, and it's not generally wise (especially if the heavier wire feeds from the panel).

    With a few specific exceptions, though, it's a fairly blatent violation of code to have #14 wire on a 20A breaker, even if it's only feeding fixed lighting loads.

    If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
  4. JohnSprung | Oct 11, 2006 01:07am | #10

    Absolutely no way can you have a breaker greater than 15 Amps feeding a circuit that has any #14 wire anywhere on it.  That's a great way to get loads of attention from your building inspector. 

    On a house like this, what I always recommend is taking a weekend to do a complete electrical system tune-up.  Start early on a Saturday morning, so you'll have light to see by.  Turn all the breakers off.  Open all the boxes.  Check and correct all the splices, missing grounds, back-stab devices, broken devices, etc. Pull the breakers out and check for signs of arcing.  Clean up and replace as needed. Turn circuits back on one by one, make yourself a map of what's on each circuit as you go. 

    On a really messy system, it's more cost effective and takes less time to take a complete look at the whole thing rather than to try to solve mysteries as they arise. 

     

     

    -- J.S.

     

  5. renosteinke | Oct 11, 2006 02:33am | #11

    The first thing you must realize,,electricians are NOT plumbers! That, is, we do not reduce our wire size as we proceed "downstream" of appliances.

    No matter what the anticipated loads on a circuit may be, the ONLY thing that limits the amount of short circuit current available is the size of the circuit breaker. The tables you see, listing different wire sizes with different size breakers, are based in part upon the amount of fault current the wires can handle without damage to the insulation.

    Yes, the code does have exceptions to the basic rule of 20 amp = #12 or larger rule. But, that's what they are- exceptions.

    If you have #14 anywhere in the circuit, you are limited to a 15 amp breaker.

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