MWBC's for Dedicated Circuits?

brric

This is false.

mysterylectric

Login timeouts ate two well crafted posts in a row (throttles sysadmin). Summary with have to do.

After very careful analysis I think AllanJ is only saying that you can't bridge or otherwise cross-connect the load side neutral of a GFCI outlet to the line side neutral. Read that 10 times if you have to, that's my story and I'm sticking to it.

Apparently AllanJ's "code" fails to recognize that what he describes is a not-so-special case of exactly that. True: jumping the load and line side neutrals of a GFCI outlet with a 2 inch jumper just don't work (I'll bet we've all tried it once). AllanJ is describing a "jumper", maybe 10's of meters long, which also sees or SHARES service as an MWBC neutral.

That won't work either. A short is a short is a short of course (unless the short is Mr. Ed er, I mean radio frequency), whether it's across the terminals with a screwdriver or long-pathed in the form of a misused MWBC neutral.

The problem is not that his advice is false: the problem is it's almost trivial. The problem is not that the scenarios he describes would be dangerous: it's just that GFCI's would start popping under any load other than 0.

What AllanJ describes sounds like code translated into practical/trade wisdom for using GFCI's with MWBCs. If the NEC goes so far as to point out that the load and line side neutrals of a GFCI must not be directly or inadvertently connected, I'l bet the rule is far removed from any treatment of MWBC's. But I wouldn't put it _entirely_ beyond the NEC to be redundant.

-Jeff

brric

You pigtail the neutrals at the first GFCI. A hot and a neutral go to the first GFCI as well as subsequent loads from that GFCI. The second hot and the neutral pigtailed from the line side of the panel feed goes to the second GFCI followed by it's load devices. The point is with a MWBC the splices are made before you connect to either GFCI.

mysterylectric

brric I must say as someone with a lot of experience with GFCI's and MWBC's I find your description confusing. I found AllanJ's description of what _not_ to do to be more clear. I mean, I can read into what you're saying to make it fit... but... as far as tutorials go... I dunno guy....

I hope I don't genuinely offend... all tongue in cheek...

-Jeff

brric

No problem. If you have so much experience then you don't need help.

Jim Port

All Bricc was saying is that the incoming neutral is pigtailed twice before the connection to the GFI. One pigtail goes to each GFI.

__________________
Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.

mysterylectric

>No problem. If you have so much experience then you don't need help.

The discussion wandered off topic, with my encouragement. Still curious as to whether AllanJ is getting his advice from code. And in uses and locations where MWBCs are not permitted.

>All Bricc was saying is that the incoming neutral is pigtailed twice before the connection to the GFI. One pigtail goes to each >GFI.

I figured it was something like that.

Maybe it would be a useful convention to refer to the conductors in the MWBC proper as buses. That's probably how they are best thought of, like hot and neutral buses of a physically long subpanel. "MWBC neutral bus" is unambiguous.

-Jeff

oleguy74

not really..busses are common connection points and conductors are for carring the current in individual ckts. or services.