Multi Wire Branc Circuits..

[Dennis Alwon]

This is what Al is talking about.

 

[gndrod]

Safety concern

Safety concern

Great diagram Dennis.
NEC 210.7 still requires a common handle tie for the MWBC simultaneous trip for this wiring configuration. This becomes a safety issue in instances where one branch circuit causes a blackout situation by tripping another circuit that cannot be reset immediately. The NEC needs to address this by stating how one branch circuit must not affect another critical circuit such as lighting or medical equipment using a shared neutral. I believe this is another good reason to restrict MWBC wiring in certain facility or dwelling conditions.

 

[ActionDave]

I think it is another good reason to get rid of the handle tie requirement.

 

[Twoskinsoneman]

Great diagram Dennis.
NEC 210.7 still requires a common handle tie for the MWBC simultaneous trip for this wiring configuration.

Not simultaneous trip but a means to simultaneously disconnect.
handle ties probably won't provide simultaneous trip.

 

[al hildenbrand]

Great diagram Dennis. NEC 210.7 still requires a common handle tie for the MWBC simultaneous trip for this wiring configuration.

Look at that language of 210.7, again. It says "simultaneous disconnect", not "common trip"A fused two or three pole safety switch is a simultaneous disconnect, like a handle tie.

 

[gndrod]

perfection

perfection

Thank you Jack and Al for keeping me on the straight and narrow to my lax use of the word 'trip' in lieu of "Simultaneous disconnect" as NEC language for two phase legs of a MWBC.

Whether both legs disconnect depends on the brand and type of a two pole configuration. On breaker ties, one 'tripped' handle may have a loose enough tie so as not to disconnect both circuits. A single handle double pole breaker would have been a more appropriate reference.

 

[short circuit faulted]

Lighting Circuits as MWBC

Lighting Circuits as MWBC

Although the 2011 code is prohibiting MWBC it has been used in commercial fields for years. IE 277V lighting circuits have traditionally be three hots a neutral w/ ground.
I think this becomes a matter of what code is being currently enforced as I have been in municipalities where the AHJ were using 2004 NEC as enforced standard in 2011.

Have a good day a a great holiday regardless - remember be safe out there we work with the invisible that is not afraid to reach out and touch us.

Steve

 

[hurk27]

Although the 2011 code is prohibiting MWBC it has been used in commercial fields for years. IE 277V lighting circuits have traditionally be three hots a neutral w/ ground.
I think this becomes a matter of what code is being currently enforced as I have been in municipalities where the AHJ were using 2004 NEC as enforced standard in 2011.

Have a good day a a great holiday regardless - remember be safe out there we work with the invisible that is not afraid to reach out and touch us.

Steve

It doesn't prohibit MWBC's it just makes it clear that you cant place them on the same phase and run a larger neutral that it didn't prohibit in the past.