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enter image description here enter image description here enter image description hereenter image description hereenter image description hereenter image description hereI was recently updating a couple light fixtures in my house and I discovered both are supplied with 14 gauge wires. The circuit for the lights runs off a 20A breaker and contains receptacles as well. The receptacles are rated 15A and are wired with 12 gauge. I want to replace the 20A breaker with a 15A breaker in order to protect the 14 gauge wire to the lights. Can this be done by simply swapping in a compatible 15A breaker? Or is there more to it?

It's the two inner breakers that I need to downgrade; the outer ones protect circuits for the washer and kitchen receptacles, respectively, so I need to keep them.

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  • I've added your pic linked in the comments below and the comment involved. This is a critical piece of information and changes everything. Also, I've updated my answer as it does not apply to your situation, though it's generally correct. I should have known better than to answer on partial info...
    – FreeMan
    Commented May 29, 2022 at 0:03
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    Thanks for your help. Sorry I didn’t mention the tandem breakers. Since the other two circuits need a higher level of protection, I’ll need to keep two of the four 20A breakers. And that certainly does complicate this scenario. My apologies. My question now is: is it ok to rearrange the hot wires so that the two circuits with 20A breaker requirements remain on one of the existing tandem breakers? Or should I preserve the sequence/positioning by replacing both tandems with new tandem (split 15A/20A) breakers?
    – Justin
    Commented May 29, 2022 at 0:45
  • @Justin can you post a photo of the label on the inside of the panel's door please? Commented May 29, 2022 at 18:04
  • Hi @ThreePhaseEel. Is the label you're referencing the one in the picture at the top of my original post? That's the only label I see, but maybe I missed something. The label says Class CTL panel.
    – Justin
    Commented May 29, 2022 at 18:12
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    @JimStewart Every light in the house (except one) is wired with 14 gauge. Fortunately, almost all of them are on just 3 circuits. One of the circuits is protected by a 15 amp breaker. The other 2 are the ones in question. There are 7 lighting fixtures total on these circuits and one of the fixtures is on a 3-way switch (in the hall). I was hoping to just swap the breaker and avoid having to re-wire all the lights.
    – Justin
    Commented May 31, 2022 at 2:00

2 Answers 2

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Wait. Did you say "INNER"?

There is a scheme called a "Multi-Wire Branch Circuit" or MWBC where /3 cable is used, and they share the neutral. This will overload the neutral (obviously!) ... unless the 2 hot wires are placed in a very particular way. Specifically, the 2 hot wires must be on opposite poles so they are 240V apart.

When you said "Inner", my thinking is that these might be a Multi-Wire Branch Circuit. If so, not only must you place the wires correctly, but you must also use a "Handle tied" breaker. In the tandem world, this is a "Quadplex" such as a BQ215220. (which has the 15's on the outer so you'd have to change that up).

Assuming they are in fact MWBCs, and I need you to check, the terrible thing would be to buy a 1515 tandem and move the two 20s to a single tandem and move the two 15's to the other tandem. That would result in 0V between the hot wires, and overloading of the neutral.

I'm not sure that's the case for you, but you should really find out!

Why do you think it is 15A wire?

I ask because until recently, all Romex cables were white. If you're looking at white jacketed romex and thinking "white = #14" that is incorrect. You need to read the labeling on the cable jacket.

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  • So, each breaker on my panel turns off a specific group of receptacles/switches independently. And no receptacle or switch requires two breakers to be shut off. If I understand the MWBC logic correctly, this means there are no MWBC circuits.
    – Justin
    Commented May 30, 2022 at 22:17
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    The 14 gauge wire is in the electrical boxes for my light switches. I verified it's size by comparing it with the (slightly larger) 12 gauge wire that exists elsewhere in my house. I had a spare piece of light blue 12/2 that I used for comparison. I also used a nickel and dime to verify the two sizes independently.
    – Justin
    Commented May 30, 2022 at 22:20
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    @Justin No, MWBCs do not work like that. They behave exactly like independent circuits, and you wouldn't know unless you opened all the boxes and saw where 2 hots were sharing a neutral - which might only be in 1 place! You have to follow the wires and see if the cable leaving the panel is a /3 cable (black and red and white). Commented May 30, 2022 at 22:24
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    @Justin Follow the hot wires from the breakers themselves to where they enter the edge of the panel from a cable or conduit. Make sure each hot has a partner neutral. Like I say, MWBCs can "mimic" regular circuits in all respects except for what I just said. Commented May 30, 2022 at 22:31
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    @Justin if you check in the panel (where the wire comes out of the cable) that is pretty much canonical. If you confirm independent neutrals there, you need look no further. Commented May 30, 2022 at 22:44
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Warning!

While this answer is generally correct, it is NOT correct for the OP's situation. The picture of the tandem breaker was added after this answer was written and up voted.



Yes, with the correct 15A breaker for your panel, you can simply swap a 15A for 20A breaker. If the existing breaker is AFCI and/or GFCI, it's highly recommended to replace it with a new breaker with identical functions, as there's likely a good reason for it to be there.

Be sure you're comfortable working with the cover off of the breaker panel - there's a lot of danger in there if you're not careful. I'd strongly recommend having someone there with you, just in case.

NOTE: If you're renting, this is NOT something you're legally allowed to do, nor is the property owner. It must be done by a licensed electrician. This is for both your protection and the landlord's.

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  • Thanks for the response. One of the fixtures is in the kitchen, but the receptacles and remaining fixture are in the family room. I also have an identical problem with a circuit that spans two bedrooms (7 receptacles, 3 light fixtures). I think the breakers are fairly old. Both belong to separate tandem sets (with 2 breakers in each slot.) I don’t see AFCI/GFCI listed on either breaker. Does the kitchen fixture require a GFCI breaker?
    – Justin
    Commented May 28, 2022 at 21:59
  • Kitchen receptacles should be gfci (either at the receptacle itself or at the breaker), but fixtures don't have to be gfci. Post a pic or two of your panel and you'll get information about the breakers. (Hint: some are bad.) Commented May 28, 2022 at 22:29
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    Additional tip: when you change breakers, it's a really good idea to use a torque screwdriver to tighten the wire down. If you can't find one to borrow, basic ones aren't terribly expensive. Commented May 28, 2022 at 22:31
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    @Justin I'm not sure if your links are valid or not or what they're pointing to, but if you've got pics of the breakers, please edit your original question then use the "sun & mountain" button above the text edit box to embed the pics into the original question. Also, please include a picture of the ID label (brand, model number, etc.) on the inside of the panel. It's always possible that the existing breaker doesn't belong in the panel, so the panel is the source of truth on what breakers belong.
    – FreeMan
    Commented May 28, 2022 at 23:30
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    OK, thanks. It looks like BD1520 are available at Lowe's (<$15). I watched a few videos on swapping breakers and it looks straightforward (shut off power to panel, remove cover, check for voltage, detach hot, pull and unhook the old breaker, hook and push the new breaker, reattach hot; etc.) I just need to make sure I know which breaker(s) to use; and I need to be certain I'm not overlooking anything critical. I noticed all the neutral wires in my panel are tied together, separate from the breakers, so I'm guessing the neutrals don't come into play, but I need to verify that, as well.
    – Justin
    Commented May 29, 2022 at 1:48

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