Common v Independent Trip with MWBC

[TwistLock]

Doing an Eaton flex retrofit and had a question about Common vs Independent trip with regards to MWBC’s.

For (quad) breakers I understand that 2 pole ‘common’ trip means ‘internal’ automatic trip of both poles (2 out of the 4 in breaker in this case) as well as handle ties. Whereas 2 pole ‘independent’ trip means handle tie(s) only.

It’s my further understanding that for a MWBC only ‘independent’ trip is required using handle ties. True?

If true, is there any reason I couldn’t use a 2 pole ‘common’ trip for a MWBC as well ?

 

[winnie]

You are required to have the handle ties. You are permitted to have common trip but it isn't required.

It is a design issue. You might prefer to not have both halves of the circuit trip together.

 

[LarryFine]

Your understanding is absolutely correct.

 

[TwistLock]

Thanks guys, tight schedule today and only certain stock available & didn't want any inspection issues - appreciate the speedy replies.

 

[wwhitney]

It’s my further understanding that for a MWBC only ‘independent’ trip is required using handle ties. True?

True per 210.4 if the MWBC supplies either (a) only 1 piece of utilization equipment or (b) supplies only line-to-neutral loads. If you had an MWBC that supplies an L-L load along with another load, then you would need to use common trip.

Cheers, Wayne

 

[TwistLock]

Would instinctively put a dryer or range circuit (with a neutral) on a common trip but didn't realize L-L was only allowed as an exception.
"...where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch circuit overcurrent device."
So "opened by the overcurrent device" is clearly not the handle tie.

 

[wwhitney]

Would instinctively put a dryer or range circuit (with a neutral) on a common trip but didn't realize L-L was only allowed as an exception.
"...where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch circuit overcurrent device."
So "opened by the overcurrent device" is clearly not the handle tie.

Another exception is when the MWBC supplies only one piece of equipment. That's why my statement specified an L-L load as well as a second load.

Cheers, Wayne

 

[LarryFine]

Bottom line is that a 2p (or 3p) breaker covers all situations.