277v lighting w/common trip breaker

[AKsparky1]

Is it permissible to install one neutral conductor with three ungrounded conductors serving 277v line to neutral loads if the three line to neutral circuits originate from a 3P common trip breaker for high bay hps lighting?

 

[iwire]

Is it permissible to install one neutral conductor with three ungrounded conductors serving 277v line to neutral loads if the three line to neutral circuits originate from a 3P common trip breaker for high bay hps lighting?

Yes and it is very common to do so.

 

[roger]

Yes and it is very common to do so.

Agreed and up to few years ago it was the pretty much only way we wired commercial lighting, of course we didn't need the multi pole or handle tied breakers.


Roger

 

[infinity]

This was always the way that we had done it in the past prior to the simultaneous disconnect rule. You cannot use a MWBC for emergency lighting.

 

[ActionDave]

Never done it any other way before the handle tie rule, I would still use MWBC today in spite of it but I haven't done very much new construction the last few years.

 

[Dexie123]

This was always the way that we had done it in the past prior to the simultaneous disconnect rule. You cannot use a MWBC for emergency lighting.

That's good to know. Where can I find that in the nec?

 

[iwire]

That's good to know. Where can I find that in the nec?

700.19 Multiwire Branch Circuits. The branch circuit
serving emergency lighting and power circuits shall not be
part of a multiwire branch circuit.

So as long as the MWBC is all emergency we are good to go.

(A MWBC by article 100 definition is a single circuit)

 

[infinity]

So as long as the MWBC is all emergency we are good to go.

(A MWBC by article 100 definition is a single circuit)

This was a code change for 2014 and the purpose is to not have two or three circuits open at the same time so you can not use MWBC's for emergency.

13-118 Log #3367 NEC-P13 Final Action: Accept
(700.19 (New) )
________________________________________________________________
Submitter: James T. Dollard, Jr., IBEW Local 98
Recommendation: Revise text to read as follows:
700.19 (New) Multi-wire Branch Circuits. The branch circuit serving
emergency lighting and power circuits shall not be part of a multi-wire branch
circuit.
Substantiation: This proposal is modeled after the requirements added to 517.18(A) and 517.19(A) in the 2011 NEC ® . The requirements were added to Article 517 to prevent the unnecessary opening of the other one or two poles of a multi-wire branch circuit because of an overload, ground fault, or short circuit on one pole of the multi-wire branch circuit. Emergency power and lighting circuits have the same need for continuity of service. For example,reliability is certainly decreased when a short in a 277 volt lighting ballast takes out the other two poles of a three pole circuit breaker, knocking out the
remaining 2/3 of the lighting. With this proposed requirement only the 1/3 of the lighting on the affected pole is out, leaving 2/3 of the lighting in operation. It should be noted that as per 240.15(B)(3), a multiwire branch circuit supplying 277-volt lighting requires a common trip circuit breaker which results in the loss of multiple lighting branch circuits when one circuit is subjected to an overcurrent.
Panel Meeting Action: Accept
Number Eligible to Vote: 18
Ballot Results: Affirmative: 18

 

[iwire]

This was a code change for 2014 and the purpose is to not have two or three circuits open at the same time so you can not use MWBC's for emergency.

It says I can't use part of a MWBC.


I know what they where going for, I don't think the words really say it.

 

[GoldDigger]

It says I can't use part of a MWBC.


I know what they where going for, I don't think the words really say it.

No, it says that the circuit you use cannot be part of an MWBC. In this case I would say that being the whole MWBC would indeed be (a large) part of the MWBC.
I would also have a problem with how you would make each and every 277V fixture use all three phases of the MWBC. If you did not do that, then the two wires feeding a fixture would define a branch circuit which is not the entire MWBC.

 

[iwire]

No, it says that the circuit you use cannot be part of an MWBC. In this case I would say that being the whole MWBC would indeed be (a large) part of the MWBC.
I would also have a problem with how you would make each and every 277V fixture use all three phases of the MWBC. If you did not do that, then the two wires feeding a fixture would define a branch circuit which is not the entire MWBC.

Why make it tough?

700.19 Multiwire Branch Circuits. Multiwire branch circuits shall not be permitted to serve emergency lighting and power outlets