Balanced neutral?

[JGinIndy]

What would be the risks of connecting it properly?

As far as ?...... simultaneously disconnecting, common trip?

 

[infinity]

What would be the risks of connecting it properly?

IMO wiring it incorrectly at the panel has a greater risk than what may or may not have been miswired somewhere downstream. Often someone comes in a moves breakers around in the panel or adds twins and ends up with the MWBC being on the same "phase". In those situations the rest of the circuit is wired correctly.

 

[electrofelon]

As far as ?...... simultaneously disconnecting, common trip?

As in there has been lots of discussion/drama about "investigating the entire circuit", discussing with client, change order etc. Is there a scenario where something bad would happen reconnecting it has a proper multiwire? The only thing I can think of is if the ungrounded conductors are connected together downstream somewhere so you would have a bolted short, but that's super easy to test for....

 

[James L]

What would be the risks of connecting it properly?

When I was wiring back in the 90s, up to "01, I worked with some real bozos. Numerous times, and I really mean numerous, somebody would run a 3-wire home run, and somebody else would feed the end with another home run. Double feeding, let's say black circuit.

MWBC typically get landed with red on B leg and black on B leg

If that 2-wire "extra" home run Gets landed on the B leg, It was dead short. I've seen it numerous times, the easiest fixes to pigtail The black and red from the MWBC on the finish.

Inspector never catches it. Then maybe 25 years later when there's a panel change out, it gets hooked up correctly and it's tripping 2 breakers. Then what?

 

[electrofelon]

When I was wiring back in the 90s, up to "01, I worked with some real bozos. Numerous times, and I really mean numerous, somebody would run a 3-wire home run, and somebody else would feed the end with another home run. Double feeding, let's say black circuit.

MWBC typically get landed with red on B leg and black on B leg

If that 2-wire "extra" home run Gets landed on the B leg, It was dead short. I've seen it numerous times, the easiest fixes to pigtail The black and red from the MWBC on the finish.

Inspector never catches it. Then maybe 25 years later when there's a panel change out, it gets hooked up correctly and it's tripping 2 breakers. Then what?

Well that is essentially the scenario I mentioned, where you have parallel conductors/double feeding. You would have to decide whether to keep them paralleled, disconnect and cap one, or try and find it. My point was of you fix an apparent multiwire that was hooked up wrong, you will know right away if it was a multiwire originally hooked up wrong or something else. If nothing trips, I can't think of any lingering unsafe condition.

 

[James L]

Well that is essentially the scenario I mentioned, where you have parallel conductors/double feeding. You would have to decide whether to keep them paralleled, disconnect and cap one, or try and find it. My point was of you fix an apparent multiwire that was hooked up wrong, you will know right away if it was a multiwire originally hooked up wrong or something else. If nothing trips, I can't think of any lingering unsafe condition.

If you had the same scenario with a double fed circuit, But it's the black one that's double fed, You can have Both of those breakers on the same leg and never know there's a problem . But if you turn off one of those Breakers, it's back fed And now it's hot in the panel. Or if you turn off one of those Breakers and you think everything is dead on that circuit, now you got a live circuit to somebody might be working on . Just because it doesn't trip, that doesn't mean there isn't a problem.

But in the case of one that is tripping Because it's double fed on the red, The quickest "fix" is just to swap the black and red on A and B so it doesn't trip anymore. That was the suggested fix at one shop I worked for. Now you go Change the panel some years later, you hook it up correctly, and two of the circuits are tripping. You don't know if it's one circuit that's accidentally double fed or if it's actually two circuits that got joined together somehow.

That's what's being discussed here. What do you do about it? Do you fix it on your own time or do you mention it as an unforeseen and charge it as an extra?

 

[electrofelon]

If you had the same scenario with a double fed circuit, But it's the black one that's double fed, You can have Both of those breakers on the same leg and never know there's a problem . But if you turn off one of those Breakers, it's back fed And now it's hot in the panel. Or if you turn off one of those Breakers and you think everything is dead on that circuit, now you got a live circuit to somebody might be working on . Just because it doesn't trip, that doesn't mean there isn't a problem.

But in the case of one that is tripping Because it's double fed on the red, The quickest "fix" is just to swap the black and red on A and B so it doesn't trip anymore. That was the suggested fix at one shop I worked for. Now you go Change the panel some years later, you hook it up correctly, and two of the circuits are tripping. You don't know if it's one circuit that's accidentally double fed or if it's actually two circuits that got joined together somehow.

That's what's being discussed here. What do you do about it? Do you fix it on your own time or do you mention it as an unforeseen and charge it as an extra?

I cant help but think there is excessive hand wringing going on here. Something being double fed has nothing to do with a MWBC. I don't, and I don't think many people do, check for double fed branch circuits when doing a panel change. Just energize one leg of MWBC to check that the black and red weren't connected together somewhere. If they were cap one, label it and move on. If not, land it properly and move in. Treat yourself to a milkshake while you're at it.

 

[James L]

I cant help but think there is excessive hand wringing going on here. Something being double fed has nothing to do with a MWBC. I don't, and I don't think many people do, check for double fed branch circuits when doing a panel change. Just energize one leg of MWBC to check that the black and red weren't connected together somewhere. If they were cap one, label it and move on. If not, land it properly and move in. Treat yourself to a milkshake while you're at it.

I'm not talking about just generically checking to see if there are any circuit switch or double fed. I'm talking specifically about a multiwire branch circuit that is tripping the breaker on one leg, and also tripping another breaker at the same time.

Then somebody just swaps red/black to opposite legs and the "issue" goes away.

If you go and change that panel 20 years later, And you run into that scenario where two breakers are tripping at the same time because you connected it properly, it's just a hack job to put a wire nut on one of them and walk away

 

[electrofelon]

it's just a hack job to put a wire nut on one of them and walk away

IMO it's not. I just don't see what the problem is. Certainly label it. Pull it out of the panel and terminate it in a box if you want.

 

[Jerramundi]

The substantiation is in the intended design, and the fact that it's possible to overload the neutral which makes an unsafe condition.

Don't get it twisted, I 100% agree that this creates an unsafe condition and merits intervention, unless you can quantitatively prove the neutral can handle the total load... but, as I'm sure you're aware in dealing with NEC requirements, "intended design" is NOT explicit substantiation.

 

[Knuckle Dragger]

Wondering how you guys handle balancing a neutral on an existing job (residential 3 wire). Either doing a panel change or working in a panel, you come across a multi wire branch circuit with both hots on the same phase.
Do you leave it that way? re install it that way after a panel change? Install the hot conductors on separate phases and hope all is correctly wired in those circuits? Splice the hots together and create one circuit? advise the costumer, trace out the circuits in the field and put them correctly on separate phases?

Thoughts?

Thank you

I don't leave it that way.
I typically inform the home owner of the issue and wire it properly if there is a problem I address it. I have also pigtailed the red and black to make it one circuit

 

[James L]

IMO it's not. I just don't see what the problem is. Certainly label it. Pull it out of the panel and terminate it in a box if you want.

The problem is you don't know if it's one circuit that got double fed, or if it's two circuits that got connected together somewhere, like a hallway 2-gang switch box.

The number of openings could be 10-15, or could be 25-35

Maybe it's a house that was wired pre-'96 and the bathroom gfci is fed from the lights, coming off a mwbc and also backfed from another bathroom gfci that's also got its own home run.

They could have all kinds of hot curlers, etc in both bathrooms and not know they have 20-24 amps draw. Then you disconnect one and cap it, and they don't know they have a problem until both their daughters are getting ready to go out next Saturday night.

Then it's overloading the breaker. It needed to be addressed, but you capped it just to make the breakers stop tripping.

 

[Jerramundi]

Of course it's justified, in fact how would an inspector who writes up the violation know that it wasn't wired correctly in the old panel and that the guy doing the upgrade made the mistake? A miswired MWBC gets a violation write up every time in my book.

From a safety standpoint, yes it is justified. But from an "existing work" standpoint, I don't think it's so clear.
I disagree that the NEC + Local Requirements explicitly mandate that existing MWBC's be corrected during a panel upgrade.

The only thing explicitly mandated is the fact that the panel was changed and the OCPD's now require simultaneous disconnecting means, which I suppose is impossible to accomplish without correcting the issue and placing the ungrounded on separate phases.

However, if the branch circuits were not modified, I don't see how you could explicitly substantiate a requirement to update the existing branch circuits during a panel upgrade.

Should the incorrectly done MWBCs be corrected? Absolutely, yes.

 

[Jerramundi]

I'm not saying it shouldn't be done... I'm just trying to think of what the explicit NEC + Local Requirement substantiation would be for doing so.

Like, if you were an electrical inspector, failed someone for this, and they had the stones to challenge you and ask for an explicit NEC or building code reference, what would your answer as an inspector be??

 

[LarryFine]

Another place separate circuits often meet up is in switch boxes near the kitchen sink.

 

[infinity]

I'm not saying it shouldn't be done... I'm just trying to think of what the explicit NEC + Local Requirement substantiation would be for doing so.

Like, if you were an electrical inspector, failed someone for this, and they had the stones to challenge you and ask for an explicit NEC or building code reference, what would your answer as an inspector be??

I would start with common snese. There is no argument, a 3-wire MWBC cannot have both circuits on the same "phase" due to the potential to overload the neutral. It doesn't matter how it was wired before you changed the panel. Just like saying to the inspector "well the old fuse panel had 30 amp fuses on all of the #14 and #12 AWG circuits so I just put the circuits back on 30 amps breakers".

 

[James L]

Another place separate circuits often meet up is in switch boxes near the kitchen sink.

I just corrected one last week. Guy couldn't understand why his hot plate tripped all his lights and microwave over the stove, which used to be a hood.

Somebody joined the c.t. recep with sink light switch, then took the #12 off the breaker and capped it

 

[hbiss]

I wire nut the two hots together with a pigtail to a breaker. If it's a 15A circuit likely there isn't going to be a high current draw. If you want check each leg with your amp meter. That will eliminate any safety issues with the neutral and pass inspection. Tell the customer about it and ask them to note anything not working or unusual. Ask if they want you to investigate further.

Collect your money and go home.

-Hal

 

[Jerramundi]

There is no argument that a 3-wire MWBC cannot have both circuits on the same "phase" due to the potential to overload the neutral.

For starters, can you please clarify what you mean by this...
Seems like an odd combination of negatives. There is NO argument that you CANNOT have both circuits on the same phase.... BECAUSE of the potential to overload the neutral??

It doesn't matter how it was wired before you changed the panel. Just like saying to the inspector "well the old fuse panel had 30 amp fuses on all of the #14 and #12 AWG circuits so I just put the circuits back on 30 amps breakers".

Also, not entirely the same thing. I agree that a panel upgrade, per explicit code requirements, requires you to put the properly sized OCPD's in place according to conductor sizing per 240. What I'm talking about, is branch circuit upgrades triggered by a panel upgrade.

I agree that this should be fixed, but if he were to just put this back as was (on the properly sized OCPD's of course), I don't see how code/local requirements merits the failure of a panel upgrade inspection.

By that logic, every single branch circuit in the panel should be inspected in its' entirety, prior to being energized, as part of a panel upgrade. Which may not necessarily be a bad idea, but merited by code/local requirements?

 

[infinity]

For starters, can you please clarify what you mean by this...
Seems like an odd combination of negatives. There is NO argument that you CANNOT have both circuits on the same phase.... BECAUSE of the potential to overload the neutral??

Sorry typo. I've fixed it.