GFI's and a MWBC

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fauxfly

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So going back to apprentice theory...I pull a mwbc from a 3phase panel, set three gfi's. Why would I get nusance tripping if I pigtail out the nuetral on each gfi. Won't the GFI electronics strictly compare amperage in on the hot, as to what goes out on the nuetral, regardless of what is going on with the home run nuetral. I know, I know, I'm losing it. Any helpful explanation guys.

S
 
Are you pigtailing the hots as well, or line-loading them?

Pigtailing should prevent tripping. Line-loading them will trip them 100% of the time.
 
480sparky said:
Are you pigtailing the hots as well, or line-loading them?

Pigtailing should prevent tripping. Line-loading them will trip them 100% of the time.


I think the OP has (1) GFI for each circuit. So none of the hots would be pigtailed, they would each be dedicated.


fauxfly said:
3phase panel, set three gfi's.

I may be wrong :D
 
mwbc to 3 GFIs, a hot goes to the line side hot of each gfi, a neutral from the MWBC neutral goes to each line side neutral. Downstream loads protected by the GFI load terminals need individual H+N connected to the load terminals of each gfi.
 
wireguru said:
mwbc to 3 GFIs, a hot goes to the line side hot of each gfi, a neutral from the MWBC neutral goes to each line side neutral. Downstream loads protected by the GFI load terminals need individual H+N connected to the load terminals of each gfi.

If you're line-load protecting downstream receps, then you'll need 3 seperate neutrals, one for each hot.

This MWBC will trip the GFCIs:

2cirgfirecepMWBC.jpg




This will not:

2cirgfirecep.jpg
 
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480sparky said:
If you're line-load protecting downstream receps, then you'll need 3 seperate neutrals, one for each hot.

This MWBC will trip the GFCIs:

2cirgfirecepMWBC.jpg




This will not:

2cirgfirecep.jpg

yeah thats what i was saying. you can use the mwbc neutral to feed the gfis, but you have to have individual neutrals fed from the load terminals for anything downstream
 
i had this same problem once with a MWBC and gfci's. you need to replace every receptacle to GFCI's since it wont work with line loaded gfci's with a pig tailed neutral. i believe this has something to do with the neutral only carrying back unbalanced current instead of ful lcurrent like a 2 wire circuit uses
 
Thanks guys, as usual very helpful. I'm going to do something different here anyway. I no longer think a MWBC is the way to go for the cust.

Thanks again troops

Steve
 
electricalperson said:
i had this same problem once with a MWBC and gfci's. you need to replace every receptacle to GFCI's since it wont work with line loaded gfci's with a pig tailed neutral. i believe this has something to do with the neutral only carrying back unbalanced current instead of ful lcurrent like a 2 wire circuit uses


You could just use a 2-pole GFCI breaker and protect both circuits. No changing of any receptacle required.
 
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