Interesting Problem

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JFletcher

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Williamsburg, VA
This past Saturday I was doing some work at an old residence. One problem I ran across was an upstairs receptacle that I could not secure power to unless I turned off two 15 amp breakers. The breakers were a tandem on a multiwire branch circuit. Nothing in the panel looked out of place. I assumed that the ungrounded conductor of one circuit is crossed with an ungrounded conductor of another circuit on the same leg in the panel, however that does not make any sense, because the breakers are shut off we're on different legs. I measured 120 volts between hot and neutral on the receptacle in question. I'm stumped as to how that circuit is being basically double fed. The panel had Bryant Breakers I think it was a 60 or hundred amp panel. Thoughts? ETA... If The Minis on a Bryant panel are on the same leg that would make sense but I always thought that it would be on different legs. Now that I think about it more, one breaker space in the panel, and both of those Breakers would be on the same leg so they shouldn't be a multiwire branch circuit correct? That would also explain the burned up neutral I found.
 
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JFletcher said:
Now that I think about it more, one breaker space in the panel, and both of those Breakers would be on the same leg so they shouldn't be a multiwire branch circuit correct? That would also explain the burned up neutral I found.
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I don't fully understand the situation. But I am reasonably certain that a set of two mini breakers would attach to the same phase of the panel's bus bars.

 
It sounds like you are saying that the receptacle is dead until you shut off two single pole breakers, on the same "side" of the panel, and then the receptacle has power.

Whooooeee ! !

A whole lotta more information is needed. The burned neutral is a hint. . . but that fundamental mis-wire of a multiwire simply hollers that there are going to be additional elementary wiring errors.
 
JFletcher said:
This past Saturday I was doing some work at an old residence. One problem I ran across was an upstairs receptacle that I could not secure power to unless I turned off two 15 amp breakers. The breakers were a tandem on a multiwire branch circuit. Nothing in the panel looked out of place. I assumed that the ungrounded conductor of one circuit is crossed with an ungrounded conductor of another circuit on the same leg in the panel, however that does not make any sense, because the breakers are shut off we're on different legs. I measured 120 volts between hot and neutral on the receptacle in question. I'm stumped as to how that circuit is being basically double fed. The panel had Bryant Breakers I think it was a 60 or hundred amp panel. Thoughts? ETA... If The Minis on a Bryant panel are on the same leg that would make sense but I always thought that it would be on different legs. Now that I think about it more, one breaker space in the panel, and both of those Breakers would be on the same leg so they shouldn't be a multiwire branch circuit correct? That would also explain the burned up neutral I found.
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I think you answered your own question here. Tandem's or twins only connect to one bus in a panel, so someone essentially paralleled two 15 amp overcurrent devices - this misapplication allows up to twice the current on the common neutral conductor of the circuit to be allowed without tripping anything.
 
JFletcher said:
This past Saturday I was doing some work at an old residence. One problem I ran across was an upstairs receptacle that I could not secure power to unless I turned off two 15 amp breakers. The breakers were a tandem on a multiwire branch circuit. Nothing in the panel looked out of place. I assumed that the ungrounded conductor of one circuit is crossed with an ungrounded conductor of another circuit on the same leg in the panel, however that does not make any sense, because the breakers are shut off we're on different legs. I measured 120 volts between hot and neutral on the receptacle in question. I'm stumped as to how that circuit is being basically double fed. The panel had Bryant Breakers I think it was a 60 or hundred amp panel. Thoughts? ETA... If The Minis on a Bryant panel are on the same leg that would make sense but I always thought that it would be on different legs. Now that I think about it more, one breaker space in the panel, and both of those Breakers would be on the same leg so they shouldn't be a multiwire branch circuit correct? That would also explain the burned up neutral I found.
Click to expand...

jumper said:
Best that I can figure out is that his return key/button is broken.

Prolly just needs to clean the keyboard.
Click to expand...

Apologies for the typos font and spacing I'm talking from my phone for the first time
 
kwired said:
I think you answered your own question here. Tandem's or twins only connect to one bus in a panel, so someone essentially paralleled two 15 amp overcurrent devices - this misapplication allows up to twice the current on the common neutral conductor of the circuit to be allowed without tripping anything.
Click to expand...
Yes you are correct. It's so seldom that I run across tandem or mini breakers that I didn't think about that initially. Somewhere the wires from those Breakers are crossed up somewhere in the house requiring both Breakers to be turned off to secure power to that circuit.
 
With both breakers on, did you check for voltage to ground from the neutral side of the recept? I would bet the recept is on the same phase as the tandem. You may have voltage on both sides of the recept with no return path.
 
JFletcher said:
Yes you are correct. It's so seldom that I run across tandem or mini breakers that I didn't think about that initially. Somewhere the wires from those Breakers are crossed up somewhere in the house requiring both Breakers to be turned off to secure power to that circuit.
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Is there two neutrals or is it a failed attempt at a proper MWBC, or worse yet someone thought doubling them up in that way is like putting in a single 30 amp breaker?
 
kwired said:
Is there two neutrals or is it a failed attempt at a proper MWBC, or worse yet someone thought doubling them up in that way is like putting in a single 30 amp breaker?
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Looks like a failed attempt at a multiwire branch circuit there should be a second neutral wire but there is not. There were many other problems at this house one of which was a bath fan wire with 14/3 with the ground snip off the red wire hook to the ground screw on the switch the white wire tied in with the neutrals and the black wire on a traveler on a 3-way switch with no power feed. They are also asked me to look at their Plumbing while I was in the crawl space LOL. Sometimes you just have to talk aloud two people who understand what you're talking about. Not like you can talk to the wife at 3 in the morning with a problem like this LOL
 
JFletcher said:
This past Saturday I was doing some work at an old residence. One problem I ran across was an upstairs receptacle that I could not secure power to unless I turned off two 15 amp breakers. The breakers were a tandem on a multiwire branch circuit. Nothing in the panel looked out of place. I assumed that the ungrounded conductor of one circuit is crossed with an ungrounded conductor of another circuit on the same leg in the panel, however that does not make any sense, because the breakers are shut off we're on different legs. I measured 120 volts between hot and neutral on the receptacle in question. I'm stumped as to how that circuit is being basically double fed. The panel had Bryant Breakers I think it was a 60 or hundred amp panel. Thoughts? ETA... If The Minis on a Bryant panel are on the same leg that would make sense but I always thought that it would be on different legs. Now that I think about it more, one breaker space in the panel, and both of those Breakers would be on the same leg so they shouldn't be a multiwire branch circuit correct? That would also explain the burned up neutral I found.
Click to expand...

What were you using to check voltage with?
 
if turning off 2 breakers makes recep hot, and turning either or both breaker back on makes it dead,

there has to be another breaker involved?

would be interested in hearing solution
 
JFletcher said:
This past Saturday I was doing some work at an old residence. One problem I ran across was an upstairs receptacle that I could not secure power to unless I turned off two 15 amp breakers. The breakers were a tandem on a multiwire branch circuit.
Click to expand...

JFletcher said:
Looks like a failed attempt at a multiwire branch circuit there should be a second neutral wire but there is not.
Click to expand...


I think it probably started out as a MWBC way back when and was wired correctly. Over the years either a homeowner or handyman decided they needed space for a new circuit.

We don't have many MWBCs here in residential but I have seen this problem a lot in commercial. A lot of people doing simple electrical work just don't have the training needed to do so. They just don't get the idea of different phases. If you find a burned neutral it's a good idea to check which phases the hots are landed on.

After you work in the electrical field for many years it's hard to remember a time when you didn't know how to wire a multiwire branch circuit but the truth is that everyone had to learn at some point.
 
growler said:
I think it probably started out as a MWBC way back when and was wired correctly. Over the years either a homeowner or handyman decided they needed space for a new circuit.

We don't have many MWBCs here in residential but I have seen this problem a lot in commercial. A lot of people doing simple electrical work just don't have the training needed to do so. They just don't get the idea of different phases. If you find a burned neutral it's a good idea to check which phases the hots are landed on.

After you work in the electrical field for many years it's hard to remember a time when you didn't know how to wire a multiwire branch circuit but the truth is that everyone had to learn at some point.
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Then there are some that wire them, but still don't know why they work like they do and therefore don't know when they did things wrong. If you have 120 volts where you wanted it, it must be right.
 
readydave8 said:
if turning off 2 breakers makes recep hot, and turning either or both breaker back on makes it dead,

there has to be another breaker involved?

would be interested in hearing solution
Click to expand...

You are thinking of "securing (getting) power" as making the receptacle hot, while the OP is using the term to mean "making secure (not dangerous)" as in not hot.
 
I believe ge's twin breakers will work on different phases. You can buy a twin double pole breaker also ---2- dp breakers that fit in the space of 2 standard size breakers.
 
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