multiwire branch circuit question

[charlie b]

The install described is 12-3 Romex - two ungrounded and one grounded.

I see that now (it's in post 9).

 

[winnie]

But it also causes the breaker's handle to move to a middle position (i.e., between ON and OFF ). That may or may not cause the other breaker's handle to move far enough from it's ON position to turn off the second pump.

But if you mechanically lock the handles in the ON position, this failure mode is prevented. Breakers are 'trip free' and may be locked ON.

I have no problem with using an MWBC for this application, with the proper breaker setup.

 

[ActionDave]

I like the breaker lock idea. I may use it in the future.

I would have no problem doing the install being discussed in my own house without a handle tie. Prior to 2008 I would have no problem doing it in a customer's house. From 1900 to 2008 MWBC without handle ties were normal, then a bunch of hand wringing ninnys finally got their way and 210.8(B) ruined every generation of electricians that came after it.

 

[roger]

then a bunch of hand wringing ninnys finally got their way and 210.8(B) ruined every generation of electricians that came after it.

Exactly!!!!!!!!!

 

[Fred B]

Question for the membership. The word "romex" has been interpreted by those who have posted replies as meaning two ungrounded conductors, one grounded ("neutral") conductor, and one EGC. Is that necessarily true? Could this romex run have included two neutral conductors? I just want to pin this detail down before the OP needs to take any corrective measures.

Yes that cable assembly is 12/2/2 or 14/2/2.
I think primary reason used resulted from AFCI breakers not working on a typical MWBC and this configuration is not technically a MWBC as it is not using a common neutral.

 

[kwired]

I absolutely agree that this is a safety issue if someone is doing electrical work on the circuits. I specifically mentioned the issue of being shocked by the neutral with only one of the two breakers off.

I absolutely agree that this is a violation of current code. Thanks tthh for providing the date of the change.

But what is the safety issue if electrical work is not being done?

-Jonathan

None, someone working on it is only reason for the rule.

We used to be allowed to connect things this way 35-40 years ago. Was a rule that all conductors supplying same yoke needed common disconnection before it eventually went to all MWBC's.

Handle tie on Homeline like OP has will not trip adjacent breaker when one of them trips. However you will end up shutting non tripped one off to be able to reset the tripped one, if you don't want to go through extra steps of finding a way to remove the handle tie or bypass the currently closed breaker somehow when performing the reset.

 

[kwired]

Once the installation is made code compliant, that may not be true. The code required handle tie may open the second breaker if the first one trips.

Never seen a QO or Homeline do that. May be some chance but risk is pretty low

 

[don_resqcapt19]

Never seen a QO or Homeline do that. May be some chance but risk is pretty low

An engineer from one of the major breaker manufactures told me that for two single pole breakers it is about 30% to 40% of the time, and for three single pole breakers it is almost zero.

Have seen it a few times...enough times that for the application in this post, I would not use a multiwire circuit.

For the 2 pole QO, I would agree that the "pin type" handle tie would probably never cause the second breaker to open...if you are careful there is often enough slop in that handle tie that you can turn one breaker off without turning the other one off. Their 3 pole handle tie is a much better design and easier to install.