Multiwire Branch Circuit?

[BigE]

I have some electrical plans coming up that will require 240v power so I took a look at the inside of my circuit panel to see what I'm working with. In doing so, I noticed a 15 amp double breaker installed, but not labeled. I followed the wires down to the bottom of the box (all other circuits go out the top). I found two 2-conductor cables exiting the box. There is a standard outlet immediately below the panel that was obviously a retrofit due to some poor drywall work and dark brown outlet (all others are your typical 80's almond). Each black wire connects to the terminals on the double breaker. Each white wire connects to the neutral bus bar. The ground wires are twisted together inside the box with only one of them extending all the way back to the ground bus bar. I'm not yet able to pull the outlet to verify due to access, but it appears that both of these cables go to that one standard outlet. I verified with my MM that both outlets have 122 volts. When I flip the 15A double breaker, that outlet drops to near zero. The curious thing is one of the outlets on the receptacle shows 2 Volts when the circuit breaker is off, but only one of them. The other shows fractions of a volt.

I've never seen anything like this before, but after some research, it sounds like it may be a multiwire branch circuit. However, I can't figure out why anyone would wire a standard outlet that way, especially so close to the panel. I wouldn't mind keeping that outlet location as it does come in handy. However, removing that double breaker will allow me to move forward with my 240v plans so I think it's going to have to go - or least be wired to a standard single 15A breaker.

All that being said, could anyone offer some suggestions as to why this might be wired this way? I want to go into this eyes wide open before I change anything and that's just not making any sense to me. Also, is there anything in particular I should verify when I remove it? Being so close to the panel, I'll pull the receptacle, wire and all so I won't need to cap anything off (I hope).

 

[JeepJohn62]

My guess is that the person wanted dedicated outlets for a freezer or other similar appliance.

I doubt this is a common configuration.

John

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[wyliesdiesels]

Someone didnt know what theyre doing.

A multi-wire branch circuit would need 1 3 cndr w/ ground cable. NOT 2x 2 cdr cables

 

[Colorado Squarebody]

Big E
On the receptacle there is a small tab that goes between both screws on each side of the receptacle. if that tab is cut then you would be able to put to separate circuits on one duplex receptacle. So each half of the receptacle would be a dedicated circuit. That would explain the breaker tie and the dual Neutrals.
I hope this helps
Landon

 

[sberry]

You need some pics and a little more hands on research. Not clear if its a tandem or 2 pole.

 

[dscheidt]

Someone didnt know what theyre doing.

A multi-wire branch circuit would need 1 3 cndr w/ ground cable. NOT 2x 2 cdr cables

There's nothing wrong with using two 2-conductor cables, instead of one 3-conductor one. It's very common to run a MWBC as a three wire circuit until the first device, or a branching point, and then run the two branches off in totally different directions on two two wire cables. It's goofy to have the split in the box, as one of the reasons they're used is to reduce the number of cables in the box.

the way this is done suggests the lack of 14/3 NM, not lack of knowledge.

 

[Citation]

You need some pics and a little more hands on research. Not clear if its a tandem or 2 pole.

This is what I was thinking. It would seem really odd to setup a MWBC with separate wires right out of the panel. I guess if there was some reason why you needed the outlets on different circuits but must have both powered off at the same time... for some reason other than being a MWBC.

 

[Terry D]

With the breaker on, put one of your meter leads in the hot side of the top half of the duplex and the other in the hot of the bottom half. If you read 240volt or close to it, then as already said, someone split the receptacle for 2 separate 15 amp circuits. They could have done it with a 14-3 wire going to it, but nothing bad will happen with they way they did it, there is just a extra white wire. The 2 volts that you are reading when the breaker is off is nothing to worry about. Its just picking up inductance.

If you don't read 240 volts, and read zero, with the breaker on, then only 120 volts is going to it and the other wire is feeding something else.

Good point by Sberry, this could be a tandem breaker, which would change everything. Please post some pictures

 

[alfredeneuman]

There's nothing wrong with using two 2-conductor cables, instead of one 3-conductor one.

What about this?

NEC 300.3(B)
B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter,cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1)through(B)(4).

 

[slow]

Wouldn't this be 2 circuits, so technically not a violation?

 

[BigE]

It is a 2 pole circuit breaker as it is connected to separate busses and takes up 2 slots. I've got a dead vehicle limiting access to the outlet. I hope to be able to get it mobile tomorrow evening so I can take a closer look. Thanks for the replies and stay tuned for an update.

 

[nadogail]

I need a picture.

 

[wyliesdiesels]

There's nothing wrong with using two 2-conductor cables, instead of one 3-conductor one. It's very common to run a MWBC as a three wire circuit until the first device, or a branching point, and then run the two branches off in totally different directions on two two wire cables. It's goofy to have the split in the box, as one of the reasons they're used is to reduce the number of cables in the box.

the way this is done suggests the lack of 14/3 NM, not lack of knowledge.

Actually its a code violation as alfred pointed out above.

Wouldn't this be 2 circuits, so technically not a violation?

Nope. Its one circuit- multiwire branch circuit. Not circuits...

 

[alfredeneuman]

If the neutrals are tied together it's also a violation of the parallel conductor rule (minimum size of 1/0).

 

[Citation]

Not an electrician here so I'm asking as much as telling.

It appears that what the OP has described is one outlet where the individual receptacles have been isolated and fed by two different circuits.

So ignoring the receptacles on the end for the moment, this doesn't sound like a MWBC to me as it sounds like the hot and neutral wires are independent from the breaker to the receptacle. The only part where they share any common electrical path is the ground wire inside the box (the two are tied together before being tied to the ground bar). The other place would presumably be the receptacle ground.

While I understand receptacles have tabs that can be removed to isolate the outlets. This is common when say the top is attached to a light switch while the bottom is always live. However, I don't think I've seen that on different circuits/phases. Is it allowed to have a double receptacle fed by two breakers and/or lines?

Regardless of code, it seems that the person who put this in wanted to make sure both outlets were powered down at the same time.

I would presume the difference in voltages on the two lines would simply be phantom voltages.

 

[alfredeneuman]

While I understand receptacles have tabs that can be removed to isolate the outlets. This is common when say the top is attached to a light switch while the bottom is always live. However, I don't think I've seen that on different circuits/phases. Is it allowed to have a double receptacle fed by two breakers and/or lines? .

Yes. Separate circuits to 1 device yoke are required to have either a double pole breaker or listed handle ties, but they wouldn't qualify as a MWBC
Both receptacles of a 1/2 hot switched outlets are usually on the same circuit btw.

 

[Citation]

Yes. Separate circuits to 1 device yoke are required to have either a double pole breaker or listed handle ties, but they wouldn't qualify as a MWBC
Both receptacles of a 1/2 hot switched outlets are usually on the same circuit btw.

That all makes sense to me. I can't think of a time where I've ever seen a switched outlet not on the same breaker as the non-switched but I didn't know if this was because of code or simply because same circuit is the most obvious way to do it.

Thanks for the education!

 

[Terry D]

With out proper pictures, we cannot jump to the conclusion that this is a violation of the NEC. What we do know is that we have a 2-pole breaker feeding (2) 2-wire nm-b's going to one duplex receptacle. We know that the ungrounded conductor tab has been broken off, isolating the top and bottom . What we dont know is if the grounded conductor tab has also been broken off. If it has, then you have 2 seperate circuts each feeding 1 receptacle on a common yoke. There is no paralleling of the grounded conductor, since it is not shared . And since it is on a 2-pole breaker, it is completely legal, no violation. But without seeing it, we dont know if it is a violation or not




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[sberry]

I did one of these a while back because putting a ceiling fixture in was a real problem. I took a chunk of 12 3 conductor that day for just such animal.
This isnt related to the nature of mwbc but,,, since its ****** drywall dont be scared to open it up. I got in a kitchen counter the other day by cutting out for a 4x4 from an existing 2x4. Was super neat, the guy was impressed as there was no refinish for the new work, I could fish 2 new wires up. If a guy wants 2 new circuits i just as soon use un modified duplex, use 2, have done this every which possible way. Moved in a place and the kitchen was part of a general 15,, ****, 70 ft and simply use a 3 conductor, power 2 new duplex.
Dont be scared to fix or replace this, tear it out, see exactly what they did, if you wanna use it replace correctly.

 

[AntonLargiader]

If the guy who wired it was just going from the panel to a recep below it, I can totally see him not sweating the 12/2 vs. 12/3 thing. May not be legal but I just don't see it as a big deal. The wiring will be obvious to anyone who is there. Just put them both on one breaker to free up the slot you need, and all will be well. You can probably even pull the extra wire out.

 

[BigE]

Here's a picture of the panel and of the outlet. The 15 amp 2-pole breaker directly under the main (brown lever) is the one in question. As you can see in the outlet picture, it is wired with 2 nm cables. You can also see that the bridge that was mentioned by someone earlier has not been cut.

I also caught my neighbor as he was walking up the street and asked him about it. He's lived next door since before this house was built and has known every occupant, including his own kids. He didn't know anything about the outlet specifically, but he knew the people. No one but the first owner back in the 80's would have attempted this. Looking at the wiring, the blocking and the drywall, he had no idea what he was doing. I think he assumed that every terminal needed a wire so he hooked up 2 wires. My neighbor's recollection of him reinforces that conclusion.

With the mystery solved, I'm going to completely reverse it. Breaker, wiring, blocking, and outlet are all coming out and I'll repair the drywall. The panel could use a good vacuuming as well. Thanks for all the feedback as I worked to figure this out.

 

[wyliesdiesels]

so the receptacle was done wrong then

you should replace those 2 double pole GE breakers on the upper right, as well. That is a bryant panel and those are not listed for use in Bryant panels

 

[BigE]

so the receptacle was done wrong then

you should replace those 2 double pole GE breakers on the upper right, as well. That is a bryant panel and those are not listed for use in Bryant panels

Thanks, Wylie. I noticed that as well. The upper breaker will be removed entirely as part of the de-****-ification of the previous work. The lower one will be replaced with the correct Eaton BR breaker.

Interestingly enough, that was originally a 40 amp breaker when I was buying the house. My inspector noted that the A/C unit it powers required a 30 amp. The A/C system had just been replaced a few months earlier so the owner called the company back to fix it. Unfortunately, it wasn't reinspected afterward so no one caught the incorrect type breaker.

 

[sberry]

How is this not tripping the breaker?
Just curious as to how the inspector determined the AC breaker? He look on the data plate or at the wire?

 

[Terry D]

How is this not tripping the breaker?
Just curious as to how the inspector determined the AC breaker? He look on the data plate or at the wire?

Even though it doesn't show it, the hot tab has obviously been broke off, separating the top and bottom. If not, it would be a leg to leg short and trip the breaker.


Edit: if you were talking about the AC breaker, disregard
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[Bad Habit]

I bet there's more outlets fed by those 2 romexs. If the bridge wasn't broken on the receptacle, there would be a dead short, no way around it. The extra set of wires is just feeding to another receptacle or ?? somewhere, same with the 2nd romex.

 

[sberry]

No, I meant the recept. It has to be open between them if the breaker was ever turned on.

 

[Terry D]

No, I meant the recept. It has to be open between them if the breaker was ever turned on.

Correct, if both the hots coming off that 2-pole breaker just go to that receptacle, the hot tab has to have been broke off, separating the top and bottom.

 

[sberry]

Yes, I posted it in the context regarding the op,, he mentioned it wasn't split but it has to be. It would be worth looking closer.
We get a lot of how too with complicated ideas here. There is a fascination with 4x4 with me bc. I use them on occasion and have done them with cable when I over think things,,, used to do it more but really avoid it in most residential if it's practical and have really made it a practice to use 1 circuit to a box and rarely even use a recpt switch in the same one if they not on the same circuit.

 

[wyliesdiesels]

How is this not tripping the breaker?
Just curious as to how the inspector determined the AC breaker? He look on the data plate or at the wire?

The tab on the hot side of the outlet is broken

The AC breaker size is determined by nameplate listing

 

[sberry]

I know this, it was really a question for the op, was wondering how they came to the conclusion. Did the inspector simply look in the panel and look at the wire or did he follow up and look at the tag

 

[BigE]

I know this, it was really a question for the op, was wondering how they came to the conclusion. Did the inspector simply look in the panel and look at the wire or did he follow up and look at the tag

Yes, the inspector looked at the outdoor unit ID plate to determine the correct breaker size.

Regarding the outlet, some of the mystery has been solved. I pulled it out today and opened up the drywall. The guy had no clue what he was doing. He covered the hot side with black tape, but once I removed that, I found that the bridge had been cut as many had predicted. However, the neutral bridge was still intact. So that's how it was working in this odd configuration. There's still no explanation for why it was done this way rather than just running a single 15 amp breaker and a single Romex cable like any other outlet.

Thank you all for your comments and feedback trying to help me figure out what was going on here.

 

[CJ7VFR]

...There's still no explanation for why it was done this way rather than just running a single 15 amp breaker and a single Romex cable like any other outlet....

Maybe the original owner was using two high draw tools/items in that location at the same time, and he needed more than just a single 15 amp circuit to run them due to tripping a single circuit.

Jim

 

[slow]

Maybe the original owner was using two high draw tools/items in that location at the same time, and he needed more than just a single 15 amp circuit to run them due to tripping a single circuit.

Jim

Exactly why I would have done that, but it would have been fed with 12/3 OR a square box with 2 duplex receptacles on their own circuit.

 

[Citation]

For what little it's worth I would prefer the idea of two separate duplex receptacles. I don't like the idea of flipping a breaker not killing the power to both receptacles. In the case of two duplex receptacles I would label each to make it clear they are on different circuits.

 

[wyliesdiesels]

For what little it's worth I would prefer the idea of two separate duplex receptacles. I don't like the idea of flipping a breaker not killing the power to both receptacles. In the case of two duplex receptacles I would label each to make it clear they are on different circuits.

Ummm the breaker would need to be handle-tied since they share the same yoke.

 

[Citation]

Ummm the breaker would need to be handle-tied since they share the same yoke.

OK, what constitutes a single yoke? A web search (which is not the same as "code says" suggests the frame that holds the individual outlets in a duplex outlet is the yoke.
https://diy.stackexchange.com/questions/133104/what-is-a-yoke-in-nec-electrician-parlance
If I put two duplex outlets
https://www.homedepot.com/p/Leviton...-Outlet-White-10-Pack-M24-05320-WMP/100055784
in a plastic 2 gang box does that make all four outlets part of the same yoke? What if I the two duplex outlets in a metal box
Plastic box
https://www.homedepot.com/p/Carlon-...rical-Switch-and-Outlet-Box-B232ACP/202065285
metal
https://www.homedepot.com/p/Steel-C...re-Handy-Box-Case-of-8-2G4DV1234-8R/202590014

What I proposed was basically two duplex outlets in a common 2 gang box. If the box is the yoke then yes, these are a common yoke. If not then these are separate. I could certainly see why everything in a multi-gang box should be powered down at the same time.

My description however was ambiguous. It would have applied to the case where two single gang boxes were placed near one another which would them make them normal, independent circuits.

 

[alfredeneuman]

OK, what constitutes a single yoke?

The yoke is the (usually metal, sometimes plastic) strap (where the screws go in) of 1 outlet or switch.

 

[Terry D]

A yoke is the ******** a single device that attaches it to the box. There can be a lot of configurations, a single receptacle, a duplex receptacle, a single switch, double or triple switch, etc

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[Terry D]

The yoke is the (usually metal, sometimes plastic) strap (where the screws go in) of 1 outlet or switch.

That might be confusing for some that are not in the trade. Its for a single device, which can have multiple outlets or switches. Someone might think 1 outlet or 1 switch means a single outlet or switch.

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