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Thread: Wire size question

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  1. #1
    Automotive Locksmith jparrie's Avatar
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    Default Wire size question

    If I have a circuit with 14 guage wire and a 15 amp breaker, can I tee off or extend that circuit using 12 guage wire? It seems that as long as the breaker is sized at 15 amps, the smallest wire size (14) would be adequately protected, and the 12 would be over protected.

    Of course that's just me. I have someone telling me that you can never do such a thing. So the question is:

    1. is it a code violation?
    2. if it is, what is the theory behind it.

    Thanks

  2. #2
    Plumber jimbo's Avatar
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    OK, this is a plumber talking, not an electrician. I have just enough knowledge about electricity and codes to be dangerous, as they say!

    I don't think it would be a code violation, as long as you did not run that 12 guage to a 20 amp receptacle.

    Let's wait for speedey or bob for your official answer. The rationale for NOT doing it, code or not, would be that in the future, someone might just see that 12ga. somewhere, and assume that they could upgrade the BREAKER to 20 amp. That would be a problem!

  3. #3

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    No, you can not mix wire sizes on the same branch circuit.

    The reason is someone may install a larger breaker thinking that all the wire in that circuit is the larger size.

    In your case, some future do-it-yourself owner of your home may measure the wire size at the outlet, then assume all the wire is that size, then not even look at the wire size in the panel and then install a larger breaker.

    Best that everything be straight forward and consistent.

    Also if you sell your home in the future, a home inspector might catch this. If they see some things like this not done to code, then they will look very closely at everything else, then report these things to the potential buyer. Might kill the sale!

  4. #4
    Moderator & Master Plumber hj's Avatar
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    Default wire

    Rational reply, but;
    1. What inspector is going to remove an outlet to check wire sizes, especially since he would have to remove ALL of them to verify any discrepencies.
    2. If the user knows enough to check an outlet for wire size, and is smart enough to find which breaker feeds it, the assumption would be that he is also smart enough to recognize the breaker wire size.

  5. #5

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    Quote Originally Posted by hj View Post
    Rational reply, but;
    1. What inspector is going to remove an outlet to check wire sizes, especially since he would have to remove ALL of them to verify any discrepencies.
    2. If the user knows enough to check an outlet for wire size, and is smart enough to find which breaker feeds it, the assumption would be that he is also smart enough to recognize the breaker wire size.
    Actually home inspectors find all sorts of "handiwork" done by do-it-your-selfers all the time. Some of them do remove outlet covers to peek inside, although mostly they are looking for a two wire no ground going to a 3 prong outlet with a jumper from neutral to ground on the outlet (a no no). Or no box installed (outlet just placed in wall).

    So far as using larger wire for the entire circuit, that is ok. It is MIXING wire sizes on the same branch circuit which is the problem.

    As to people doing dumb things, you would not believe what people can do to their electrical wiring...

    Here is one from a home inspector's forum where someone replaced the fuses with copper pipe!
    http://www.inspectorsjournal.com/For...?TOPIC_ID=7705

    Here is one from the same forum where a home inspector found a neutral to ground wire on an outlet (clue was he removed the breaker panel cover and noticed there were no ground wires)...
    http://www.inspectorsjournal.com/For...?TOPIC_ID=7501

  6. #6
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by Billy_Bob View Post
    So far as using larger wire for the entire circuit, that is ok. It is MIXING wire sizes on the same branch circuit which is the problem.
    Why do you feel that this is a problem?

  7. #7
    In the Trades Bob NH's Avatar
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    Quote Originally Posted by Billy_Bob View Post
    No, you can not mix wire sizes on the same branch circuit.

    . . . . .

    So far as using larger wire for the entire circuit, that is ok. It is MIXING wire sizes on the same branch circuit which is the problem.
    Billy_Bob; please cite the National Electrical Code paragraph to support the statements from two of your posts as quoted above; or acknowledge that there is no code to cite.

  8. #8
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by Billy_Bob View Post
    No, you can not mix wire sizes on the same branch circuit.

    The reason is someone may install a larger breaker thinking that all the wire in that circuit is the larger size.
    This is incorrect. Larger sized conductors are installed all the time to confiscate for voltage drop in such things as well pumps and the like.

    Quote Originally Posted by Billy_Bob View Post
    In your case, some future do-it-yourself owner of your home may measure the wire size at the outlet, then assume all the wire is that size, then not even look at the wire size in the panel and then install a larger breaker.
    In this case it would be the idiot that was doing the work at that time that would be making the mistake not the original installation.

    Quote Originally Posted by Billy_Bob View Post
    Best that everything be straight forward and consistent.
    So how would you wire a well pump that is 200 feet in the ground and 200 feet away from the house?

    Quote Originally Posted by Billy_Bob View Post
    Also if you sell your home in the future, a home inspector might catch this. If they see some things like this not done to code, then they will look very closely at everything else, then report these things to the potential buyer. Might kill the sale!
    If a Home Inspector wrote an installation up as being incorrect as outlined in the original post then the Home Inspector should be reported as not knowing how to properly do his job.

    The bottom line is the installation as outlined is perfectly legal and compliant.

  9. #9
    Electrician Johnny C's Avatar
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    Default Wire Size Quest.

    The NEC does NOT prohibit properly connecting a number 12 awg Cu conductor to a number 14 awg Cu conductor that has overcurrent protection rated at 15 amperes. This is no different than connecting number 12 awg Cu directly to a 15 ampere overcurrent device. In some instances a conductor sized based in accordance with the load and overcurrent device might terminate in a junction box, and due to a lengthy circuit or feeder, the conductor size is increased to compensate for voltage drop. However, due to the terminal size, the larger conductor would not fit in the terminal, and the smaller size conductor was used to connect to the fuse or CB.

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