Is it against NEC code to use 12/2 gauge wire for receptacles and 14/3 light fixtures in California?

Question

I've been searching for answers but most of the questions involve using two separate gauges for the same circuit.
I'm in the process of upgrading to a 200 amp service and I changed out all the receptacles for a 12 gauge circuit with a 15 amp breaker as a preventative measure to upgrade to 20A later in the future.
The problem is the cost of 12/3 is double the cost of 12/2. My light fixtures are going to be run using 14/3 on a separate 15A circuit.
I've read the NEC2017 book and understand that you need at least 14 gauge minimum to run anything with 15A. So my question is, will I fail inspection if I am using 14/3 gauge wire on a separate 15A breaker for my light fixtures/switches but a 12/2 gauge wire on another separate 15A for my receptacles?

Jim Stewart · Accepted Answer

Since the OP is a software engineer he might well be interested in the fact that there is an alternative way to wire a pair of what we in the US call "3-way" switches. The traditional way in the US is called 2-wire control, and the new alternative is called 3-wire control.
To implement 2-wire control there needs to be a /3 cable between the two switches and to implement 3-wire control there needs to be a /4 cable between the two switches.
AFIK the advantage of the 3-wire control is that there is a continuing line hot in both switch boxes whereas with 2-wire control the line hot in one switch box is interrupted during the process of switching at the other box. AFIK this would only be important if there was an active device in that box that required a constant line hot.
One thing though would that if later you wanted to put a receptacle near that switch box, you would be able to get an unswitched line hot and neutral from that switch box.
EDIT
Another feature of 3-wire control is that the same wire between the switches is always the line hot in both boxes. With 2-wire control the hot switches from one traveler to the other when the "line switch" is flipped.
With 2-wire control one switch is the "line switch" (common connected to the line hot) and the other switch is the "load switch" (common connected to the load).
But with 3-wire control both switches are hard connected to the line hot, and both switches are hard connected to the load. Any active device that will work in one switch box will work in the other. The arrangement is symmetrical.

Ecnerwal · Answer

15A (duplex) receptacles are fine on a 15A or 20A circuit. The only
place you MUST have a 20A outlet is if it's the only outlet (simplex,
and only one of it) on a 20A circuit. You can have more 20A outlets,
but you don't need them. They are rated for the use (and usually if
you see some sort of 15A only language molded in, you will see that
it's about using the backstab connections, which you should not use
anyway, and they don't fit 12Ga wire)
12Ga wire is fine on a 15 or 20A circuit.
14Ga wire is ONLY fine on a 15A circuit.

In modern practice where you must supply neutral to switch locations:
Typically, you only need /3 wire for "what would have been a switch loop" (I suppose it still is, just less confusing to neophytes than the hot white version) and between 3-way switches unless doing a Multi-Wire Branch Circuit (MWBC) - which you don't mention.
So, if power runs to the light switch, and then power runs to the lights, /2 is fine everywhere on that light circuit. If power runs to a light, and then a single cable runs to a switch location, that cable needs to be /3. Or you can run two cables to the switch location (depending on the relative price of buying /3 cable .vs. the hassle of running two cables.) If you have a 3-way switch setup, you need /3 between the two switches.
Or perhaps you are confused about wire gauges? 12 Ga is LARGER than 14Ga. so 14Ga minimum, means not a larger number (smaller wire) than 14Ga.

Harper - Reinstate Monica · Answer

Cost wise I would be more worried about having to buy many spools  of wire.  Cheaper to buy 250’ of #12 than 100’ of #12 and 150’ of #14.  Price it.
All your 15A circuits must be laid with wire that is at least 14 AWG copper. You are always allowed to use bigger wire anywhere you want. (although it can be confusing if the wire going into the panel is #12 and wires farther down the circuit are #14).
All your 20A circuits must use 12 AWG wire or larger. You can use larger wire anywhere you want.
15A receptacles are allowed on 20A circuits as long as the circuit has at least 2 sockets (any duplex recep will suffice).
A circuit with all #12 wire and all 15A receps, can be characterized as either a 15A circuit or a 20A circuit at your discretion.

Is it against NEC code to use 12/2 gauge wire for receptacles and 14/3 light fixtures in California?

3 Answers

Add your own answers!

Ask a Question