mixing 14-gauge NM and 12-gauge

I told my son in-law not to mix 14-gauge NM and 12-gauge NM backed with a 15amp breaker; but I still think he thinks I am blowing smoke. I can not find reinforcement on the net or in my Michigan Code book Help! d:-[

 

both 14 and 12 gauge will be protected by a 15A breaker. Code states that 14Ga will be protected by an overcurrent device of not more than 15A and 12GA by 20A.

 

Thanks Scott for the reply 14 backed by 15 amp and 12 backed by 20 amp is a given.

But in Michigan and my guess in most states you cannot mix the two together even if the breaker is for the smaller wire.
The code is written to protect the unwise not the wise. With only the above knowledge the next home owner would think that if he found a 12 gauge wire it would be good for 20 amps. I do believe there is a heat transfer problem to the breaker also mixing 14 and 12. I had an inspector make me yank it on my first remodel.
Trust me DON'T DO IT.
Scott you sound just like my Son In-Law, and I like him to.

 

14 and 12 are both ok behind a 15amp breaker, but you must use one or the other and not both. Mixing 12 and 14 on a single breaker will not pass inspection here in PA. I know someone who decided to run 14 for light switches on circuits fed by 12... did not pass and were told to pull and replace.

 

Thank you you and anyone from any other state.
Does anyone have a code # in reference to not mixing 14/12?
I have the national code numbers for the amp to gauge rule but could not find the one about not mixing.
Thank you all again.

DGifford d:-}

 

On a 15 amp breaker, you can certainly use #12 wire. There is nothing wrong with this. You may want to use the #12 for voltage drop reasons or inventory purposes.
If you feed your lights with #14 off of a #12 which is fed from a 15 amp breaker there should be no problem. If the inspector balks at this, ask him for a Code reference. If he can't provide it, which he can;'t, then he has no case. And he MUST be able to provide a Code referene for any violation.
There is a point about a future homeowner becoming confused and automatically thinking that #12 means "Ah-ha = #12 must mean a 20 amp circuit, but then fools shouldn't mess with wiring.
~Peter

 

Peter, if assuming someone used the same wire size on a whole circuit makes you a fool, what exactly does that make an engineer?

 

Does anyone have a code # in reference to mixing 14/12?

 

Thanks I hope we will find this out; this is the very reason why I posted it. (I would love to here from some inspectors)

You are sill in the trades it sounds like so I have a question on this long 12g run with 14g at the end......... If the 14g line gets overheated how long will it take this long 12g wire to heat up at the breaker?
Next Question if you had this long of a run that you feel you need to run a 12g to feed it should you not run even a larger gauge to a small sub panel? I wonder why they use GFIs for lighting circuits above a sink is John Q dumb enough to stand in the sink bare footer to change a light bulb. (Not really a question)

Don’t you think this has turned out to be a good posting?

IS THERE ANY INSPECTORS OUT THERE

 

John, the problem I see with the example in your previous post (a long run of 12 gauge from 15 amp breaker to a distant room, then 14 gauge used to wire the room) is that the next home owner, upon repeatedly tripping the breaker on that circuit (from running a large air conditioner, perhaps?), will open the breaker panel, see 12 gauge wire attached to the blown breaker, and immediately assume that it is ok the replace the 15 amp breaker with a 20 amp breaker, because the breaker is feeding a 12 gauge wire.

Mixing 12 and 14 gauge in the manner suggested sounds like a reciep for a future electric fire.

Now, if you start with a 14 gauge wire at the breaker, then switch to 12 gauge somewhere down the line, this is not as dangerous as vice-versa, but this should still not be done. Because wire is so cheap, there really is no logical reaosn that I can see to mix gauges on the same circuit.

dgifford, here's a suggestion: Buy your son-in-law some of the correct gauge wire, and tell him that if he wants to see any inheritance, he'll make the circuit all the same gauge.

 

Thats a great ideal

 

Some times we read to fast. "If you keep your fishing worms cold they live longer"

 

So whats the current status of this project?

I'll ask the advice of a friend that does Resi work every day. (probably the only person I would trust to wire the bedroom I sleep in other than myself, I went to school with him for electrical)
I would avoid mixing, but it is very circumstantial.
Discretion is the best tool for these situations.
I think some inspectors simply like to maku up their own rules which seem 'logical' and would provide additional protection to a unknowlegable person, which is commonly not fully-baked, inducing additional problems and risks that otherwise would not exist if the codes (both NEC and local were followed word for word. Even worse is parts of the country (esp. rural) where code enforcement is minimal, and most work is DIY.

gj

 

You guys are just asking for problems. In our screwed up society of today, mixing wires types as you claim, you will get yourself in a lawsuit. I don't care how about the 'fool' 'ignorant' etc people who see 12 at the breaker and assume. You did the original work, now someone else modified it assuming you did it the right way. I have yet to work with an electician who switches wire sizes in the middle of a run in the 15years i have worked in a commercial setting. If a fixture has a different wiresize, thats one thing, pulling mixed matched wires is sloppy in my opinion.

 

YEESSSS! Sounds like a Pro. Consumers will work on their home wiring and if they look at any information (including DoItYourSelf.com) it will tell them 12 is good for 20amp and 15 is good for 15amp and they will not look any further than that. Thanks for the common sense reply support

 

Interesting discussion, because I happen to have a neighbor wiring three 8' double flourescent fixtures in his garage/workshop for two 3-way switches right now with 12/2wg and is planning to run a single insulated 14 as the third wire.
I'm not a pro electrician, and I don't know what size breaker he's using, but I told him not to do that in any case. I highly doubt that it will pass even our rural county inspection.
Talk about mixing 12 and 14. That has got to be against code everywhere, I would think.

 

Wise electricians know how to wire correctly.

The fools doing wiring is the reason we have Codes.

 

Actually the reason we have codes is so enginers have a bible to quote from..

 

Good one Hellrazor!
And ours for guidance, esp. for lost souls in the elec. arena.
It has similarity to an encyclopedia, it is updated every 3 years.
gj

 

There are several different questions that have been asked in this post.
First off, let's make it clear that it is legal and acceptable to mix wire sizes. When I say that I mean that it is ok to mix a 14/2 romex with a 12/2 romex. I am not saying, as in one post, that it is acceptable to run a single 14 conductor with existing 12 guage cable.
There are many instances where we connect larger wires to smaller wires. This is usually done to avoid a potential voltage drop. I myself have tied #6 conductors to a pair of # 12 conductors coming out of the panel. This is usually done in places like parking lots where you are running the wires to the parking lot lights and they have to travel long distances. The use of the number six wire eliminates the voltage drop and the circuit is protected by a 20 amp breaker so those conductors terminate with a pair of #12's which are tied to the breaker.
There is NO article in the NEC which prohibits the mixing of sizes of wire!! The only thing that you must remember is that your overcurrent protection must be sized to the smallest wire. If this is done then it won't matter who comes along later and how much knowledge they have as the circuit will be protected for the worst case scenario. For example: if you mix a #12 and a #14 cable this is fine as long as you use a 15 amp circuit breaker to protect the entire circuit. It is perfectly acceptable to use a wire size that is larger than the breaker protecting the circuit will allow, it is however, not acceptable to use a wire size that is smaller than the breaker protecting the circuit, this is where you would run the risk of a fire.
The other consideration when doing this is to make sure that the devices or fixture or whatever it is that you are installing is capable of accepting the size of the wire that you are using. Most receptacles are rated for #'s 12 and 14 and in that case it would not be acceptable to terminate a #10 conductor on that device.
Hope this helps!

 

I suppose if you were building a new house and money was not tight, you could run all #12 wire and 20 amp rated outlets, switches, and fixtures, but use 15 amp breakers. This would be a bit of overkill, but would help insure that the wires don't overheat and start a fire in event of a short.

 

Actually, there are several studies that have been done on the subject of "upsizing" the wiring run in a typical home. The studies have shown that the use of #12 in place of the #14 would reduce the "minimal' voltage drop that occurs on the #14 thus saving the homeowner money in the longrun.

 

Actually, there are several studies that have been done on the subject of "upsizing" the wiring run in a typical home. The studies have shown that the use of #12 in place of the #14 would reduce the "minimal' voltage drop that occurs on the #14 thus saving the homeowner money in the longrun.
When running #12 wire it is not necessary that the receptacles be rated at 20 amps. The NEC allows the use of a 15 amp receptacle on a 20 amp circuit.

 

You're right. I saw it on this site the other day that you can go 15 amp outlets on a 20 amp circuit provided there are two or more outlets (one duplex). Still, I would be inclined to go 20 amp rated switches on a 20 amp circuit because I want to be sure teh fuze really is the weakest link and much weaker than the others.

Thanks