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Bought a house a few weeks ago and I’m in the process of replacing all my receptacles to tamper proof models. Generally all circuits in the house are 20 amps or more and replacing all the 15 amp receptacles with 20 amp receptacles have been going well.

Today I came across one receptacle in a 20 amp circuit with a hot 12 AWG wire coming in to the receptacle and 14 AWG wire going out to light fixtures/switches. No other outlet is in this circuit.

A few questions:

  1. Do I need to replace the 20 amp breaker with a 15 amp one?
  2. Does this outlet have to be a 15 amp outlet even though 12 AWG wire is coming in?
  3. Why do you think 14 AWG wire was used for lighting if 12 AWG was going in? It’s fine to use 12 gauge wires for lighting / switches right?

Thanks for the help everyone.

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    How practical would it be to simply replace the culprit wire run?
    – ThreePhaseEel
    Commented Apr 8, 2020 at 11:39
  • not very practical, but it's also not an outlet that would be used very often, so if I had to switch out the circuit to a 15 amp breaker / receptacle, it wouldn't be a problem. Just want to do the right thing.
    – BlueGuy
    Commented Apr 8, 2020 at 16:30

2 Answers 2

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1) Your first question yes you should downgrade the circuit to 15Amps because the breaker protects the wires and if the breaker is rated for a higher current than the wires in the circuit can handle there is a fire risk.

2) If you were turn the one circuit into two circuits with a 20Amp circuit and a 15 Amp circuit with separate breakers then the outlet could be kept at 20Amps but otherwise no.

3) Maybe they ran out of the larger wire and that is just used what was around.

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    1. Downsizing the breaker is certainly the easiest path in most cases, unless replacing wire is practical. Breaker must be sized for the smallest wire in the circuit. 2. many things will run fine on a 15A outlet, particularly as it's the only outlet on the circuit. 3. Ignorance + "hey, it's just lights" but mostly ignorance.
    – Ecnerwal
    Commented Apr 8, 2020 at 12:18
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  1. Yes, I would change the breaker to a 15A. You could call your local electrical inspector to see if they are aware of any past or present locally adopted exception to the NEC that allows it. You might just annoy the inspector. (Also answer to question 3 has related information.)

  2. NEC 210.21(B)(3) and it's referenced table prohibits 20A receptacles on 15A circuits. #12 isn't prohibited on 15A circuits, but for various reasons the terminals on some receptacles won't accept #12. Most circumstances you can pigtail #14 from the receptacle to #12 on a 15A circuit. Carefully read the ratings embossed on the receptacle and installation instructions on the boxes, the instructions are part of the UL/ETL/CSA Listing.

  3. Using #12 is fine for lighting on 15 or 20A circuits. There were some jurisdictions that used to interpret earlier versions of what is now NEC 210.19(A)(4) to allow #14 taps single outlet lighting circuits. I never tried to argue the current or past version with an inspector. (But I have pondered how this could be any worse than plugging a #16 extension cord into a 20A receptacle circuit, but I don't build circuits I know I will need to argue.)

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    Answer on your (3) point is right on. the #14 to a lighting circuit (not outlet) that is hard wired. The #14 is going a switch and light with no branch. The reasoning is that no light fixture is going to draw >15 amps<br />
    – Programmer66
    Commented Apr 8, 2020 at 16:05
  • I would not change the circuit breaker, as all the outlets are wired with #12 wiring. Changing the breaker to 15 amps means changing all the outlets back to 15 amp outlets
    – Programmer66
    Commented Apr 8, 2020 at 16:12
  • Interesting, so because it would be highly unlikely for lights/switches to draw so much current, then leaving the breaker and receptacle with 20 amp versions should be fine? This may be a dumb question, but the circuit currently looks like: breaker (20 amp) --12 AWG--> outlet (20 amp) -- 14 AWG--> lights/switches: if I plug something into the outlet that draws > 15 amps, would the 14 AWG wires see that current, or because the receptacle is wired before the lights, they would never see the high current. Sorry if I'm explaining this poorly.
    – BlueGuy
    Commented Apr 8, 2020 at 16:22
  • Logic explanation or not, because of a lawsuit involving a house I sold with unknown non-compliant building code issues I certainly wouldn't advise any non-compliant installations.
    – NoSparksPlease
    Commented Apr 8, 2020 at 16:24
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    @BlueGuy "because it would be highly unlikely for lights/switches to draw so much current, then leaving the breaker and receptacle with 20 amp versions should be fine?" -- no, that contradicts the core philosophy of safety. If things were designed for what should happen, we wouldn't need breakers at all!
    – Harper - Reinstate Monica
    Commented Apr 8, 2020 at 20:06

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