Multi wire branch circuit NM cable

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It's when things can go "South" ... latter when extending an existing circuit. You're under the house or in the attic and you just grab an available neutral, what are the chances of grabbing the "Right" neutral.
 
I have a PI for GFCI. Maybe, I should make a new PI for multi wire circuits ?
 

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  • NATIONAL ELECTRIC CODE 2023 - Section 200.4(C) Proposed Amendment.pdf
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mtnelect said:
Maybe, I should make a new PI for multi wire circuits ?
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Why?

A Qualified Person would not be in any more danger than he would be working on any wiring. Dumbing down the trade for the incompetents or DIYers is unnecessary.

IMO, the change to require simultaneous disconnecting of all ungrounded conductors of MWBC simply caused more service people to work hot in order to not upset those that would be affected on the other circuits.
 
In my opinion, all should be protected from unsafe wiring practices. The National Electrical Code was developed without discrimination with safety in mind for everyone.
 
The NEC was not developed as a "how to" manual and neither was this forum.
 
The thing is that before the handle tie requirement, the breakers could be scattered here and there. An installation mistake is easier to make and put both legs on the same 120V and overload the neutral. No one will ever know if those cirucits are lightly used. Or maybe, the house burns down if they are heavily used. Secondly, absent handle ties (or common trip), the neutral is a shock hazard for a person servicing anything in the house. The neutral could have current on it despite turning off the "right" breaker for whatever is being serviced. On top of that, is generally poor panel labeling, so don't depend on anyone leaving bread crumbs to follow. The handle tie (or common trip) makes installation mistakes less likely and also makes the future servicing safer.
 
Once again, let's revisit the Qualified Person. Now let's take the unqualified and put him in a center grounded delta panel, he can fry a lot of things by connecting new 120V circuits to the high leg, should center grounded delta's be illegal?
 
mtnelect said:
It's when things can go "South" ... latter when extending an existing circuit. You're under the house or in the attic and you just grab an available neutral, what are the chances of grabbing the "Right" neutral.
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You actually can't use the term "go south".. it has deep roots in, well, the south.
 
Like I said, last one I saw wrong was done by "qualified" person. I think he holds every paper they got except contractor. Panel was packed with tandems, was simple error but pretty irrelevant as was. I had to work to find a place for it to make sure I wasn't moving another multi.
It was a good place for a mistake if there is one.
 
roger said:
If lines are not on opposite phases you don't have a MWBC period.
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But couldn’t this be done incorrect by taking a multi-wire nm cable such as 12-3 with ground and wire the line leads to depot are breakers on the same phase and share a neutral.
 
Jpflex said:
But couldn’t this be done incorrect by taking a multi-wire nm cable such as 12-3 with ground and wire the line leads to depot are breakers on the same phase and share a neutral.
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You wouldn't have a MWBC. The number of conductors in a cable assembly does not determine how the cable is used.
 
I have been on forums and been at this a while. I bet I wired a garage with about every scheme they ever thought of. I get simpler all the time.
 
If the conductors are on the same phase then there wouldn't be a potential voltage difference between them. a multiwire branch circuit "consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system."
 
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