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In my panel I found a 2 pole 20amp breaker connected to 12/3. When I trace this circuit, it begins to power outlets in my dining room.

At outlet 1, the 12/3 comes in with the Red leg powering the first outlet. The Black leg enters the box, and then leaves that box to the other 4 outlets in the room. All Neutral and Grounds are connected properly.

So here's the question: It appears that this was the start of some kind of a branch circuit that got removed at some point. But since the red leg is powering exactly 1 outlet, and the black legs are powering 4 outlets and nothing else: Would it make sense to not use the red leg, put that outlet on the black leg for a total of 5, then replace the breaker with a single pole 15amp breaker? Wire nut the red in the panel and only connect the black into the 15amp single pole.

Eventually I want to replace that entire wire with 14/2 but I'd have to remove the basement ceiling.

Just seems pointless to power 1 outlet as a dedicated 20amp leg, and then 4 more on a separate leg of the 2 pole breaker. Thoughts?

EDIT: Sorry, the part I didn't mention is that leaving that first box is all 12/2 to the second outlet, and then the other outlets are wired in 14/2. So: 1 outlet on red leg 12/3. 1 outlet on black leg 12/2. 3 outlets on black 14/2 from previous outlet.

My concern with the 'double toaster' theory (which I hadn't considered, thank you!) would be that if you plugged in a heavy load in one of the 3 other outlets, you could cause an issue because 14ga shouldn't have more than 15 amps, but the breaker would be fine with it.

That's my reasoning for removing the wire and dropping down to 15 amp and 14/2. If copper prices come down I could feed that leg in 12/2, but I'll cross that bridge in the future.

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    "Eventually I want to replace that entire wire (12/3) with 14/2" - This is silly. If the extra wire bothers you that much then at least use 12/2 which is perfectly fine on either a 15 or 20 amp circuit. I believe standard procedure is to cut back the unused wire as far back in the box as possible so that it's unusable; ditto inside the panel.
    – MonkeyZeus
    Nov 30 '21 at 20:06
  • Can think of that outlet as being two different circuits. You can plug in two toasters at the same time and not trip the breater.
    – crip659
    Nov 30 '21 at 20:06
  • @crip659 If one trips then the other trips as well. Maybe the previous owner had a specific use-case for such a setup.
    – MonkeyZeus
    Nov 30 '21 at 20:07
  • I don't agree. Is #14 cheaper for a builder who buys the stuff by the mile? Of course. But for low volume DIYers, no way. You have to own #12. The upfront cost of also buying spools of #14 way, way, way exceed any per-foot savings you'll get on the smaller wire. So I just don't own any... and won't. And I buy #12 in big spools since it serves all my needs, and big spools are way cheaper by the foot. Nov 30 '21 at 22:40
  • Reducing the breaker to 15A for the circuit is good to protect the 15A wire, but NEC 210.52(B)(3) requires dining area circuits to be considered small appliance circuits, and are required to be 20A, so further work would be necessary to bring it up to code. Dec 1 '21 at 6:21
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What you have there is called a Multi-Wire Branch Circuit or MWBC

It is 1 circuit. However it provides the effect of 2 complete circuits, with only one cable.

There is nothing wrong with an MWBC. They are completely legitimate even though they are "new to you". (though they have fallen out of favor, because they are more difficult to put GFCI and AFCI protection on).

Due to Code requirements, the two breakers are handle-tied, to protect maintainers from only turning off half the circuit and then getting nailed by the other half. Use of a 2-pole 240V breaker is an acceptable way to get a handle-tie; this provides common trip which MWBCs do not need unless they also serve 240V loads. (which they can do!!)

If you are crunched for breaker spaces in your panel, and need to free up a space (a bad situation we don't like to see people in), then yes, you can downgrade it to a simple circuit. There's no need to even re-wire the circuit at all, simply land both the red and black on a 1-pole breaker. (assuming the breaker's labeling authorizes two wires per terminal; if not simply pigtail).

Or, by all means, feel free to upgrade the MWBC to its full glory. Have the red phase power additional outlets, and even attach 240V loads if you desire.

I can see someone having installed a MWBC just like that if that window was a suitable place for an air conditioner. Back in the day when air conditioners had a SEER rating of about 2, it was common to have window air conditioners that either were 240V, or completely maxed out a 120V circuit. That would allow you to go either way: a 240V air conditioner that shared with 120V receptacles, or a 120V air conditioner that used the entire red phase.

Nowadays we see SEER ratings as high as 22, so a lot of BTUs takes only a little power. (SEER = BTU/hr per watt).

Correcting the #14 flaw

You say half your MWBC (the black half) is wired with 12/3 up to the split, and then 14/2 on just the black phase.

MWBCs can do that.

Remember what I said about handle-ties and 2-pole breakers? You can use a 20A breaker for the red, and a 15A breaker for the black, and then use a listed handle-tie to tie the breakers together for common maintenance shutoff.

At that point, you lose common trip which means the circuit can no longer mix 240V and 120V loads.

If you want to do the "downgrade to a simple circuit" strategy, you need to land both hots on a 15A breaker not 20A, because the #14 wire is the lowest common denominator.

It's quite possible the original installer did it correctly, and some goober came along later, saw a 15A breaker on #12 wire and said "that can be 20A" without fully investigating the circuit.

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  • I saw a youtube video before about having two 120 outlets on different phases so you could have 240 power. I am not sure if this is just a bad youtube hack or something that is/was allowed?
    – crip659
    Nov 30 '21 at 21:04
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    Same principle but being approached from the other direction, which makes it safe. There's a gold standard for what is safe/legal called the National Electrical Code. Almost any advice you get here will conform to that. Youtube can't say the same LOL... that's what happens when you promote based on clickbait instead of quality. Nov 30 '21 at 21:18
  • @Harper-ReinstateMonica Agreed (AGAIN!) on your comments / answer...why rip out 12 ga ???? and replace with cable of lower capacity? What's the OP going to do with the ripped out wire? Sell it to a tweakers who will sell it to some shady metal recycling outfit? Sorry for the rant, but some of these questions just don't make sense. Nov 30 '21 at 21:49
  • Not ripping out the 12ga in the walls, the poorly secured feeder that leaves from the box. It needs secured, but I can't secure the entire thing because of a basement ceiling. So since it was bad craftsmanship in the install, I'm assuming it's bad in places I can't see. The plan was to replace (but leave in place) that wire by running a new run of 14 from the box since it's the smallest conductor in the wall and cheapest, but I'd probably run new 12. But instead I'm going in a different direction by changing the breaker. The question doesn't make sense when you don't have the facts.
    – Jason
    Nov 30 '21 at 22:14
  • @Jason depending on what you mean by "poorly secured", there is a perfectly reasonable possibility. Cables that are run after the walls have been closed up (old work) do not have to be secured to anything other than the boxes they terminate in. Plastic old-work boxes have tabs that you break free at one end, then push the cable from the wall, through the tab and into the box. The tab, attached at one end acts as the cable clamp. Metal old-work boxes have a screw down clamp that does the same thing. If this is what you're concerned about, there's nothing to be concerned about...
    – FreeMan
    Dec 1 '21 at 15:38
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It's a Multi-Wire Branch Circuit or MWBC. Nothing to get excited about. Ripping out the wire is a complete and utter waste of effort.

It's safe as is, leave it alone.

After the post was edited to mention 14Ga wire:

It's safe if you replace the 20A double breaker with a 15A double breaker since there is 14Ga on the circuit. There's no need to remove the 12Ga.

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  • Thanks for the help. I won't replace the 12ga in the walls, but feeding that circuit is 12/3 wire that is just being held up with a few random bent nails, so I'm pretty sure somebody added this and it's not safe. It's loosely hanging from the main beam in my basement and is not secured to anything in any meaningful way.
    – Jason
    Nov 30 '21 at 21:14
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    Add a few staples. The cable is not "unsafe" becasue it was poorly secured. Secure it. Double-check the connections if you think the support is a sign of sloppiness. If the cable is not actively damaged, it's just as safe as if it was stapled every 4 feet; and you can secure it, rather than replace it.
    – Ecnerwal
    Nov 30 '21 at 21:17
  • @Jason a bag of wire staples will cost you far less than any quantity of copper wiring available in the store today (or just about any day).
    – FreeMan
    Dec 1 '21 at 15:40

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