Just verifying if it is OK to use 12 ga wire on a 15 amp circuit.
I bought a roll of 12 ga to do some outlets on a 20a circuit in my garage. Rather than buy some 14 ga wire to do the lighting as well, I thought it would be OK to use the 12 ga.
Any issues I might need to consider?
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Replies
The only issue is the difficulty of working with the #12, and the increased difficulty of connecting the very light gauge lamp wire to heavier wire. Sometimes the wirenuts don't work as well as when all wires are similar in size. But it's done all the time.
box size
There is another issue on this: the electrical code limits the number of wires in a given size of box. The larger the wire size, the fewer wires can be in the box. A friend of mine got caught on this back in the late '80s and had to replace most of the boxes in the house he was building. Most plastic boxes have the number of wires allowed embossed in the inside of the box; metal boxes do not (you have to deduct two wires for any switch or outlet installed in the box from those numbers). The purpose of this is to reduce the chance of a box being overcrowded causing shorts and fires.
So you not only have the extra stiffness working with 12 gauge, you have the need for larger boxes or more boxes to provide adequate room for wires. There is also the extra cost of using the larger size of a metal that has become much more expensive (I've been hearing this idea of using only no. 12 for over 30 years, and it was not a new idea then!).
As far as capacity: In 1987 the Code upgraded the required insulation on wires in NM cable. Technically the newer14 gauge copper wire can carry 25 amps without danger. They left the limit of 15 amps on the circuit because there were so many houses wired with the old cables. This insulation upgrade extended to all types and sizes of wire, but the smallest sizes for branch circuits were left at 15, 20 and 30 amp breaker requirements. The real issue is heat buildup: all wire warms up from carrying electrical current, depending on size, amperage and length. The older insulations could not take as much heat. Even the heavy wires for utility distribution can carry more or less current depending on whether they are strung separately in "free air" as the Code Tables call it, or placed in conduit or buried.
My own practice? I use #12 when the Code requires it for 20 amp circuits. If I have a really long run on a 15 amp circuit, I use #12 (I did this recently when wiring a well pump on a rural job); with a long run you can have a problem with voltage drop--there are tables that tell you how long a given size can carry a given amperage). If I'm extending a 15 amp circuit to one more box and all I have handy is 12-2 w/g, I'll use it unless it causes a box problem. But in general, I'll use the smallest size wire that is adequate and legal for the job.
Except for the simplest situation I always use the largest/deepest box that will fit the location -- it's a real PITA trying to jam eight wires into a box that's supposedly "legal" for exactly eight.
Dan, I mostly use the larger boxes, too. Over the years I've done a lot of "old work" wiring, and it's a royal pain when you're trying to replace a dead switch or receptacle and find some moron ran five cables into one of the old slope-shouldered switch boxes. Too many guys in the trades in the last century did not think about the next guy who would have to deal with their work.
Some clueless inspectors have a conniption about it, while in other areas 12 is actually required for 15A circuits.
It's fine, other than the stiffness factor.
Seems 14 ga is a thing of the past around here. just make sure your outlets are 15a and not 20a.
14 ga makes perfect sense IMO. With lighting efficiencies and other electronics increasing, you can do a lot w/ a 15a circuit. Only need 20 a for the heavier duty circuits like I'm putting in the garage ... boy sure is a difference in cost w/ the 20a and 15a outlets and switches!! 20a costs like 4x what the 15a does. You fill a house w/ 20a outlets/switches and you're spending a LOT more on your electrical.
That seems strange to me. 15a/14ga makes great sense IMO for so many reasons. In this day and age of energy efficient everything (lighting, electronics, etc.), using 20a circuits for many applications makes little sense. And have you priced 20a switches and outlets?! Outlets are like $2.00 + for 20a and for 15 a they are like 70 cents. The wire is much easier to handle, too (and cheaper).
Assuming you will load up a 15a circuit w/ too much use in this day and age seems arcaic, really. While our lives are filled with all kinds of electronics and electrical devices, many of them sip tiny bits of electricity. My builder convinced me to do most of my wiring in 14ga and I'm glad I did. It really makes sense and it saves dollars!!
There is a time and place for everything, but using 12ga routinely makes as much sense as old fashioned framing techniques.
15A outlets can be used on a 20A circuit. Virtually all outlets made are rated for connecting to a 20A circuit.
And 20A outlets are only more expensive because you can't buy the super-cheap ones in 20A size most places. When you do an apples-to-apples comparison of the same quality outlet the prices are pretty much the same. (And I'd rather pay the premium for back-wired outlets, vs wrangling with a cheapie. My time saved is well worth the cost difference.)
I assumed that if it has a 15a label [embossed] on it, it couldn't be used in a 20a application.
If you look closely it will indicate it has a 20A "pass thru" rating. And, truth be told, the contacts will handle 20A. It's just that you can't plug a 20A plug (when was the last time you saw one of those?) into the outlet.
That be the case, I got ripped buying a bunch of 20a for my garage!! I'll have to check it out. I don't recall EVER seeing a 20a plug on anything. But there's a lot I don't recall sometimes. :)
It should be noted that it's a no-no to have #12 coming out of the breaker panel and then splice it into #14, even if it is a 15A circuit. There's too much of a chance than someone down the road will see the 12 in the panel and sub in a 20A breaker, assuming the entire circuit is 12.
Recently I did a job that had 14 for some of the lighting circuits but used 12 wire for the homeruns The inspector said it's OK as long as the #12 was clearly and permanently labled that it was to be used with a 15a breaker only.
Yeah, I don't think it's a violation of code (though some inspectors may flag it). It's just not a good idea (unless, as in the case you cite, the wire is clearly and permanently labeled in some fashion).
perfectly appropriate
I haven't used 14ga in residential since 1995. 12ga is my standard for 15 or 20A circuits.
15 amp only label
What exactly does one use to label the wire "15 amp circuit only"? My electrical inspector said it was OK to feed 14 gauge wiring with a 12 gauge cable from the panel, as long as the wire in the panel was labeled "15 amp circuit only".
Wire labels
Brother makes a suitable cartridge for their lablelers, and I'm sure the other manufacturers have similar tape cartridges.
You may also find wire labels preprinted at a supply house.
You can also use clear shrink wrap tube, over paper labels.
Sparky I worked with would take pieces of romex insulation, neatly letter the necessary stuff on them with an extra-sharp Sharpie, and slide them onto the loose wires. I know it sounds kinda flaky, but it looked exceptionally neat when he was done, and the labels stuck out (visually) fairly well.