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I just finished installing seven LED recessed lights in my master bedroom. I had to fish wiring through the ceiling and through the wall to an existing switch. I'm changing the one gang switch box to a two gang switch box. I got everything put in and as I prepared to wire the lights in, realized I had run 14 gauge wire, while the existing circuit was 12 gauge, because it has a 20 amp breaker. This circuit is the LED lights I just installed, a ceiling fan with LED light, and ~5 outlets in the master bedroom. The largest load I would ever put on this circuit is a vacuum cleaner.

Should I

  1. swap out the 20 amp breaker with a 15 amp breaker and make a note on the panel that there is 14 gauge wire, or
  2. bite the bullet and rewire with 12 gauge?

I'm obviously tempted to throw in a 15 amp breaker, but want to make sure I'm not missing something here.

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    The best solution is to break the circuit up into 2, because (while not against code) best practice is to separate overhead lighting from outlets in the same room. Otherwise 15 amp breaker is fine, no need for label.
    – Glen Yates
    Jul 13 at 15:08
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    @GlenYates: If the wire that attaches to the breaker is 12ga, but there is 14ga wire elsewhere on the circuit (as I understand the situation to be), I would definitely regard a tag on the wire as a good idea. Otherwise, I wonder if putting a subpanel in the bedroom might not be a bad idea, with one 15A breaker for the lights and one for everything else, all fed from the 20A main circuit? A moderate overload from the receptacles would be likely to trip the subpanel breaker before the main breaker, and thus not kill the lights.
    – supercat
    Jul 13 at 23:33
  • @supercat - Right, I missed that, I thought he had 14ga everywhere. Good catch.
    – Glen Yates
    Jul 14 at 2:27
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    In the future, would you have to remove wall cladding to rewire this? If the wall lining is already open right now, then right now is the time to do it.
    – Criggie
    Jul 14 at 9:26

2 Answers 2

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There are certain places in a house that require 20A circuits:

  • Kitchen (2 small appliance circuits)
  • Bathroom (receptacles or receptacles + lights, lights by themselves are OK on 15A)
  • Laundry Room (one required circuit)
  • Any appliance that specifically requires a 20A circuit
  • Any circuit that has 20A receptacles.

Other than that (or any other similar specific circuits), general lighting and receptacle circuits can be 15A or 20A.

Existing circuits are grandfathered if valid at the time of original installation. That includes 15A in kitchen or bathroom where 20A is required today (i.e., for any new circuits). But you can't make things worse. So, for example, if your problem circuit actually includes a kitchen receptacle (which would be grandfathered with respect to "kitchen/dining area only") then you can't downgrade it from 20A to 15A.

Most homes only have 15A receptacles, except where required for specific equipment (e.g., in a basement turned into a serious workshop), even on 20A circuits. Code allows for that: As long as you have at least two receptacles, 15A receptacles are OK on 20A circuits. And in fact most kitchens and bathrooms use the familiar 15A receptacles even when they are on 20A circuits. (Anecdotally, 20A receptacles are very common in commercial buildings, at least in my area.)

So as long as:

  • There are no kitchen or bathroom receptacles on this circuit (shouldn't be, but it happens in old houses)
  • There are no 20A receptacles, which look like this Leviton from Amazon:

Leviton 5-20

go ahead and swap the breaker. A lot easier than running new cable/wires.

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    If you're going to put in a new breaker anyway, why not make it one with arc-fault interruption? Isn't the bedroom an area requiring AFCI according to current code?
    – Armand
    Jul 13 at 17:23
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    @Armand Depends on local code adoption as to whether that's needed or not. Complication is that it isn't a new circuit but it is an expansion of an existing circuit as opposed to just straight replacement of receptacles (which usually does not require breaker upgrades). Jul 13 at 17:40
  • It may not be required given local rules - it just seems like a no-brainer good idea from what I've read (no expert on this certainly).
    – Armand
    Jul 13 at 23:56
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    @Armand Depends who you ask. There are two key concerns: cost and False Positives (a.k.a., nuisance trips). With a GFCI the cost is generally lower (because you can install it with a receptacle for ~ $20 a piece, vs. $40 or more for a GFCI breaker (and more for an AFCI breaker!), but that's not generally an option for AFCI), plus while GFCI and AFCI both have quite a bit added for self-test and other features, a GFCI at its essence is extremely simply compared to an AFCI, which results in more issues of nuisance trips due to motor loads and other stuff. And the direct benefit of GFCI is Jul 14 at 1:38
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    extremely clear - life safety around any water - where AFCI is more of a fire prevention issue, which is important but not as "no-brainer" as GFCI. Jul 14 at 1:39
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One or the other must you do.

A bedroom I would go with the 15 amp breaker.

If the wires are easy to change, you can do that also, and keep the 20 amp breaker.

A breaker change, maybe a five minute job. A wire change is much longer, without any gain.

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