The only drawback is increased cost for the thicker wire. Plus, it's a little more difficult to work with, and box capacity may become an issue in some cases.

Benefits include less voltage drop, but this only comes into play with a long run.

You can mix wire sizes, as long as the overcurrent protection (fuse or breaker) is sized for the smallest wire on the circuit. In the case of mixed wire sizes, place a note on the panel indicating that there is 14AWG on the circuit. This will prevent someone from putting in a 20A fuse or breaker later, when they see 12AWG in the panel. I prefer NOT to mix wire sizes. I would run all 12AWG and protect the circuit at 20A, unless there is some reason it is not possible.

Thanks....did not think about the potential future issue with the breaker...I will complete with 12 AWG and break with 20 AMP....that will avoid any future problems.

Again, thanks for the advice AND quick reply.

In most places it's permissible to mix wire sizes. IMO it's poor workmanship to do so.

If you wanted a ckt like this: 20A CB - 20A Recp - 20A Recp - 3 Way SW - 150W Light - 150W Light - 3 Way SW. Would it would be poor workmanship to run 12-2 to the recps, then change to 14-3 for the lights?

I don't know about poor workmanship. Workmanship to me imlpies that it is either messy, negligent, or corners were cut. I see it as only being a waste of money on the 12/2, and the possibility that someone other than you might see #12 wire and assume the whole cc't was wired #12. They then might replace the 15A breaker with a 20A. That would be a problem.

If you wanted a ckt like this: 20A CB - 20A Recp - 20A Recp - 3 Way SW - 150W Light - 150W Light - 3 Way SW. Would it would be poor workmanship to run 12-2 to the recps, then change to 14-3 for the lights?

Davey, you cannot change to 14 ga wire on a lighting/receptacle circuit protected by a 20 amp breaker. It's not about workmanship. It's about code and safety.

I ran into this kind of situation when doing an addition. The GC used 14 ga wire in some sections of say a room, say for the lighting but used 12 ga from the panel to to the room. the inspector didn't have a problem with it on the rough inspection. Several weeks (months) go by and you are ready for the final electrical....guess what: The walls are now covered up with drywall, the inspector sees 12 gauge at the panel with 20 amp breakers!!! It's OK!! the inspector does not remember that there is some 14 gauge on the circuit. A second contractor pointed this out to us and we checked with the inspection dept. and they were very surprised....they never thought of this possibility. The inspection process has a flaw. We de-rated some of the circuits. The GC doing the wiring has wired several houses like this, basically installing bigger breakers than allowed. A lot of electricians just use 12ga wire throughout. Then there is no question. That is what I would do.

My juridiction has the answer...they don't allow any 15 amp circuits. And with the wire now being color coded it's pretty easy to spot that 15 amp stuff.

the cost difference between 12/2 and 14/2 isnt that much, i would just spend the extra... btw (and this is not a sales pitch for them, i do not work for them) i got a 250' roll of 12/2 on ebay for $60 including shipping... there are alot of wholesalers selling there and alot of people who buy say 100' and only use 50' and sell the rest. get some decent prices there.

Very simply, we do not mix wire sizes on the same circuit. If we are running a 20 amp circuit, everything on that circuit is wired with 12/2. When we are running 15 amp circuits we use 14/2. As an example, all receptacles in a kitchen are run on a 20 amp circuit. Lights and under-counter lighting are usualy run on a seperate 15 amp circuit. I recently did a service call at a new home where everything in the entire house was run on 20 amp circuits. Nothing wrong with this but I think it is over-kill. Problem was a GFCI in the laundry that kept trippping. Was loose connections. Found that the two outlets in the laundry that were protected by the GFCI also protected and outside receptacle which is a major no-no. Indoor and outdoor receptacles should not be on the same circuit. Found dishwasher, disposer, GFCI protected counter outlets and overhead lights on the same circuit. So, you look at the panel and notice that the entire house is on 20 amp breakers and run with 12/2 but then you follow circuits which are wired very strangly.

"Indoor and outdoor receptacles should not be on the same circuit."

Can you site the code for this? I've read that as long as it's not
kitchen counter, bath, laundry this is permitted.

Thanks
Chris

There is no restriction on mixing indoor and outdoor receptacles, as long the outdoor receptacles are not extensions of the kitchen c/t, dining/pantry, bath, or laundry.

Biggest problem with using 12ga on lighting circuits is the mess you get with multi-gang switches. It is SO much easier to use 14ga when working with multiple switches.

I believe I told you the GFCIs were in a laundry that also included and outside receptacle. The front porch lights are also on the dining room circuit. The home owners are personal friends but live in an area where we do not work as a normal rule. These folks recently built a very nice home and had hired an "electrician", and older man, who lives about 100 miles away so he was not available to handle any problems. Understand he is around 80 and I don't know where they found him. As a result, I looked into their GFCI problems as a favor. He had not labeled the breakers so it was in the process of finding the breaker for the laundry GFCI that I began to unravel some of the strange wiring.

Now, regarding wiring with 12/2, I have said before that I can wire 2 or 3 14/2 receptacles in the time taken to wire one in 12/2. Also, it would be a real job to wire a multi-gang switch box in 12/2. Commercial jobs are another story.

I just had some wiring done in my garage. There are 7 duplex receptacles on one 20-amp circuit with 12-2 wire protected with a GFCI. The electrician installed 15 amp receptacles rather than 20 amp receptacles. I did not expressly request 20 amp devices--doh! Can I install a few 20-amp receptacles without causing problems? If I do, does the GFCI have to be 20 amp?

If you are in the US, you may have 15A receptacles (and GFCIs) on a 20A circuit, as long as you have more than one receptacle (you do). There is no need to spend the extra money for 20A receptacles (same insides, different front). If you have an appliance or tool that has a 20A plug, then you should run a dedicated circuit.

Hi .. To save on circuit breakers in a panel ,electricians often feed lighting circuits from receptacles and connect a switch .So if it is incorrect to mix wire gauges ,how is this problem solved if the receptacles have to be 20 amp with 12 gauge ?..If separate circuits are used for everything ,there are no slots left in a new panel for the future...Thank you for a response . Frank.

I have no idea what you are saying frankiedon. There's no code reason to mix wire gauges as long as the breaker is sized for the ampacity of the smallest gauge.

There are rules for the size of receptacles and the circuit ampacity (both the wiring and the breaker). It's not the case that the receptacle configuration has to have exactly the same ampacity as the circuit. Some cases it is. Some cases it is allowed to be smaller. In the case of 15A receptales, as long as you have more than one (which includes a single duplex recpetacle), you can put it on a 20A circuit. A 20A circuit may not EVER have 14g wire in it anywhere.

Ron,

>> In the case of 15A receptales, as long as you have more than one
(which includes a single duplex recpetacle), you can put it on a 20A
circuit. <<

For my understanding... If I have a 20 amp circuit and I only want to put one receptacle on it, can I use a 15 amp duplex receptacle? Or does it need to be a 20 amp duplex?

It may be a 15A duplex. A duplex receptacle is TWO receptacles.