common neutral in mwbc

[Cleveland Apprentice]

Is this true? All mwbc, single and three phase must be terminated on a 2 or 3 pole breaker? What if you run a 12/3 and split to a kitchen refrigerator and run the other to another appliance and it trips? So now the refrigerator is tripped? I can understand running a mwbc to a same device/yoke which I realize is code, but to two different and independent devices is dumb.

 

[cowboyjwc]

210.4(B)

 

[Smart $]

Is this true? All mwbc, single and three phase must be terminated on a 2 or 3 pole breaker? What if you run a 12/3 and split to a kitchen refrigerator and run the other to another appliance and it trips? So now the refrigerator is tripped? I can understand running a mwbc to a same device/yoke which I realize is code, but to two different and independent devices is dumb.

"Dumb", perhaps. But what would be even more dumb is designing and installing the MWBC you describe . Since the advent of this requirement, each refrigerator should be on individual circuit, or at the very least, a two-wire, multi-outlet circuit where other loads present minimal likelyhood of tripping breaker.

PS: The requirement isn't that you must use a multi-pole breaker. You can use handle-ties on single-pole breakers... but you still have the "risk" of common tripping.

 

[Cleveland Apprentice]

Yes now it would be a dumb install with the new requirement, but before I used to run a 12/3 and split it between a refrigerator and maybe a dishwasher. Now with the requirement of using double pole breakers or handle ties, I would probably run 12/2 for everything

 

[infinity]

I wouldn't call it dumb, albeit not the best design. How often do circuit breakers actually trip? Kitchens are one of the few places left in a dwelling where there is a practicable use of MWBC's so we still use them. :happyyes:

 

[ceb58]

Yes now it would be a dumb install with the new requirement, but before I used to run a 12/3 and split it between a refrigerator and maybe a dishwasher. Now with the requirement of using double pole breakers or handle ties, I would probably run 12/2 for everything

That's why I invested in 12-2-2/w G. One cable from panel to kitchen, 2 separate circuits

 

[infinity]

That's why I invested in 12-2-2/w G. One cable from panel to kitchen, 2 separate circuits

That would be a good alternative solution.

 

[jxofaltrds]

Is this true? All mwbc, single and three phase must be terminated on a 2 or 3 pole breaker? What if you run a 12/3 and split to a kitchen refrigerator and run the other to another appliance and it trips? So now the refrigerator is tripped? I can understand running a mwbc to a same device/yoke which I realize is code, but to two different and independent devices is dumb.

Maybe they thought that it was "likely" to land on the same yoke!

It's all about safety not about what makes our lives easier.

90.1 Purpose.
(A) Practical Safeguarding. The purpose of this Code is
the practical safeguarding of persons and property from
hazards arising from the use of electricity.

 

[ActionDave]

Maybe they thought that it was "likely" to land on the same yoke!

In comedy acts they call that a call back.

It's all about safety not about what makes our lives easier.

90.1 Purpose.
(A) Practical Safeguarding. The purpose of this Code is
the practical safeguarding of persons and property from
hazards arising from the use of electricity.

There are MWBC in my own house. They don't have handle ties. I use them every day. What hazard am I subjected to?

 

[jxofaltrds]

In comedy acts they call that a call back.

There are MWBC in my own house. They don't have handle ties. I use them every day. What hazard am I subjected to?

None unless you work live! :happyno:

http://forums.mikeholt.com/showthread.php?t=93028

 

[ActionDave]

90.1 Purpose.
(A) Practical Safeguarding. The purpose of this Code is
the practical safeguarding of persons and property from
hazards arising from the use of electricity.

I didn't ask about working on them and the code section doesn't address it either. I use a MWBC every morning when I make my coffee and toast. What hazard am I being subjected too?

 

[Smart $]

None unless you work live! :happyno:

I'd say that's the main reason for the requirement. With MWBC OCPD's not tied together, the potential exists where one believes power to a circuit has been disconnected, until the unexpected event changes that belief.

 

[cowboyjwc]

There's probably no danger to you. The danger is to your coffee maker and other pieces of equipment plugged into those circuits if you drop the neutral for some reason.