Sharing neutrals

[Therealcrt]

I have a question regarding sharing neutrals for a branch circuit.

Are sharing neutrals OK for branch circuits as long as you have handle ties On the Breakers.
Or is sharing neutrals Against code

 

[roger]

I have a question regarding sharing neutrals for a branch circuit.

Are sharing neutrals OK for branch circuits as long as you have handle ties On the Breakers.
Or is sharing neutrals Against code

MWBC's are legal, see 210.4

 

[infinity]

Or is sharing neutrals Against code

I wish I had a dollar for every time I heard that MWBC'S were banned by the NEC.

 

[Therealcrt]

I wish I had a dollar for every time I heard that MWBC'S were banned by the NEC.

OK I understand it’s not against code but if it’s such a safety violation, why is it not against code

 

[LarryFine]

OK I understand it’s not against code but if it’s such a safety violation, why is it not against code

There is no safety risk or "violation" to them for competent electricians, even before the handle-tie rule.

 

[infinity]

OK I understand it’s not against code but if it’s such a safety violation, why is it not against code

With the requirement for handle ties or multi-pole circuit breakers most of the danger has been mitigated if you practice safe working procedures.

 

[electrofelon]

but if it’s such a safety violation, why is it not against code

IF I had a dollar for every time ive heard MWBC's are a safety hazard, bad practice, should not be used, etc............ Complete nonsense.

IMO the handle tie requirement increases shock risk.

 

[brycenesbitt]

IMO the handle tie requirement increases shock risk.

What's your thesis on this one?


Internal handle ties and the external ones may have different answers. There's a certain level of qualification that should come with working on circuits, and not understanding a MWBC and "depending" on the handle tie for safety is a very poor tradeoff.

Note for the record that MWBC's also apply to 3 phase circuits for 120V legs and work great.... so it's not just split phase that gets all the MWBC fun.

 

[LarryFine]

What's your thesis on this one?

My guess: hesitance to de-energize multiple circuits to work on one, especially in, say, an office setting.

 

[electrofelon]

What's your thesis on this one?

My guess: hesitance to de-energize multiple circuits to work on one, especially in, say, an office setting.

Correct. My main client runs labs and have tons of equipment and people running processes and tests, on computers, etc. I have and will continue to usually work a circuit hot rather then the hassle of tracking down and coordinating the people and equipment on other circuits. I have done several new builds for them and I skip the metal rod on the handle tie so it can be removed to just deenergize the needed circuit.

 

[Therealcrt]

There is no safety risk or "violation" to them for competent electricians, even before the handle-tie rule.

You think? So what happens if there’s a loose neutral on an energized multi wire branch circuit?

 

[electrofelon]

Philosophically, I find the handle tie in conflict with say the HVAC disco. For the HVAC disco, I assume the thinking is you want a convenient disconnect so people wont say "oh the hell with it, ill just work it hot". The handle tie makes it not convenient to de-energize the circuit.

 

[LarryFine]

You think? So what happens if there’s a loose neutral on an energized multi wire branch circuit?

Same thing that happens if there's a loose neutral on an energized service, just on a smaller scale.

 

[electrofelon]

You think? So what happens if there’s a loose neutral on an energized multi wire branch circuit?

Every house in america is fed with a multiwire branch circuit.

 

[Therealcrt]

Every house in america is fed with a multiwire branch circuit.

That’s a statement, which isn’t 100% true, but has nothing to do with the comment I made. Do you know what happens in that scenario?

 

[roger]

That’s a statement, which isn’t 100% true, but has nothing to do with the comment I made. Do you know what happens in that scenario?

The same thing that happens when the service looses a neutral, and I would would say electrofelons statement is 99% true.

 

[roger]

Here's an example of what happens.

 

[infinity]

So what happens if there’s a loose neutral on an energized multi wire branch circuit?

We all know that the voltage on one circuit may increase while it decreases on the other circuit(s).

 

[electrofelon]

Yes if you lose a neutral on a service or MWBC, you create a series 240V circuit which can swing the voltage around and fry things. I think the key is to think critically about this. How often does this happen? Is there evidence that this happens frequently enough such that MWBC's should be avoided? Cant you say "what if I have a loose connection" to many other situations and they would result in bad things happening? What if an EGC is broken and there is a phase to case fault and someone gets shocked and killed? What if a neutral on a non MWBC comes loose and someone gets shocked on the open neutral not realizing its now "hot"? What if someone puts 14G wire on a 100 amp breaker? What if, what if , what if.......

 

[infinity]

I love MWBC's, for homeruns all the way back to the panel they were a no brainer but once the simultaneous disconnect rule entered the code they pretty much disappeared. IMO a 2-wire circuit is less dangerous but if we were still allowed to use MWBC's with just single pole breakers I would continue to use them.