multi wire branch circuit feeding two gfi's

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bth0mas20

Senior Member
Location
Maryland
My plan was to install 6 outlets total in a garage. I used a 12/3 from the panel. Fed three outlets with one 20a circuit and other 3 with other circuit.
I pigtailed the neutrals together from the panel and wire that feeds other 3 outlets.
I connected the neutral to the load of first gfi to continue to other two outlet on the first circuit. I then installed another gfi for other circuit to feed 2 other outlets. So their is a total of 2 gfis and 4 duplex outlets split in 2 each 20amp circuits. I didnt have double pole 20a breaker at the time of install so I put in 2 single 20a breakers. I installed these single breakers one over top the other so their on seperate phases. When I turn on one breaker it holds until I turn on the other breaker then they both trip and vise versa.

I was sure this is possible. Now that the sheetrock is up Im thinking I will either need to install Gfis in each outlet all to the line side or will a double pole 20a gfi breaker work and just install new outlets in place of the two gfi outlets?
 

480sparky

Senior Member
Location
Iowegia
First, you can't protect two circuits with GFCI receps in a MWBC.

Second, you need to connect the income neutral to the line, not the load terminal.

As for the breakers tripping, you've got a line-line short somewhere.
 

bth0mas20

Senior Member
Location
Maryland
Its been a while since I roughed the wire in for this so I may need to trace my wires out to make sure Im not bucking phases. My incoming neutral is tied to the line side not the load.

So can I just install 6 duplex outlets with 3 on each circuit and install a 2 pole gfi breaker?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
There is no reason your install wont work. You must have something crossed. 12/3 tied to two 12/2 cables with the neutrals all together should work. You have to have something wired incorrectly or a short somewhere.
 

jmellc

Senior Member
Location
Durham, NC
Occupation
Facility Maintenance Tech. Licensed Electrician
Either breaker works OK by itself without the other? Check all boxes containing both hots. Sounds like a hot/hot fault that only acts up with both legs live. Possibly a staple digging in, faulty joints or short in 1st box.

Disconnect both hots in your 1st box. Also, check joints for errors. I've had helpers splice 2 hots. Power up & see if they trip. If they hold, check both hots for hairline insulation cracks that may cause a short when crammed. Check for any flash marks, they may or may not be there. If they trip when hots are clearly separated, the short is between 1st box and panel. Check any wire in crawlspace that you can get to. If you find a staple short, you can cut and install a j-box to repair, probably have to do 2 unless you have a loop you can pull out, etc. If short is in a wall you may have to open it up. If you can fish to 1st box, may be easier to fish new wire up there back to whatever good point you can tie in with.

Hope you don't have to chase too many shadows. That is frustrating.
 

480sparky

Senior Member
Location
Iowegia
I gotta ask the OP:

Are both circuits going to each duplex? Are you putting one circuit to one receptacle on the strap, and the other circuit to the other half?
 
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480sparky

Senior Member
Location
Iowegia
This.......

2cirgfirecepMWBC.jpg



......will NOT work. As soon as there's a load on either circuit downstream from the GFCI, the GFCI will trip.







You either need to change it to a 2P GFCI breaker:

2cirgfibrker.jpg






Or install 2-cond. cables between the GFCI receps and the protected receps downstream:

2cirgfirecep.jpg
 
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jmellc

Senior Member
Location
Durham, NC
Occupation
Facility Maintenance Tech. Licensed Electrician
Gotcha. I now see what you meant.

I don't follow that. I've done kitchen counter circuits with a MWBC. Took 12-3 to 1st recep, pigtailed neutrals & fed 1st recep with neutral & black to line side. Feed outgoing 12-2 with red to black for 2nd ckt. Pigtail grounds as usual & attach. Never had a problem with that. If black ckt has another recep, a 12-2 feeds from load terminals out to next recep. Never had problems with that, but did have to use a larger box for box fill issues. Neutral is spliced BEFORE connecting to any loads. I don't see how a 2 pole breaker changes this in any way, except that tripping 1 automatically trips the other because of being attached. That's why I no longer use MWBC. The idea of 2 ckts is to minimize overloads & have 1 working if the other is out. 2 pole breaker defeats that, though still leaving the advantage of less labor than running 2 12-2's.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
From my read of the OP, it's wired right, as in 480's last drawing, except for a line-to-line short.

The simple test:

Check for power to the neutral bus at the breakers; you'll find both breakers' load terminals hot when only one breaker is on.

The simple finder:

Temporarily connect a light from one of the load (circuit) wires to the neutral bus. It will be on when the other breaker is on.

When you find and disturb the short, the light will go out. Ta-daa!
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
I don't follow that.
First 480 said this,
First, you can't protect two circuits with GFCI receps in a MWBC.
Then Dennis said two pole GFCI breakers don't work. I had to check the date on my calender to make sure it wasn't the first yet. When I saw it wasn't I posted "What???" That post, Dennis' post, and bunch of others were deleted for reasons that escape me. In my own house I have the same set up as you describe and 480 illustrates.
It all makes sense, but not really.
... I no longer use MWBC. The idea of 2 ckts is to minimize overloads & have 1 working if the other is out. 2 pole breaker defeats that, though still leaving the advantage of less labor than running 2 12-2's.
I hate the new rules concerning MWBC's, but I have resolved some of my anger by using 12-2-2 and 14-2-2. At least I can still get two home runs in one with it and not have to tie the breakers together.
 

kwired

Electron manager
Location
NE Nebraska
My plan was to install 6 outlets total in a garage. I used a 12/3 from the panel. Fed three outlets with one 20a circuit and other 3 with other circuit.
I pigtailed the neutrals together from the panel and wire that feeds other 3 outlets.
I connected the neutral to the load of first gfi to continue to other two outlet on the first circuit. I then installed another gfi for other circuit to feed 2 other outlets. So their is a total of 2 gfis and 4 duplex outlets split in 2 each 20amp circuits. I didnt have double pole 20a breaker at the time of install so I put in 2 single 20a breakers. I installed these single breakers one over top the other so their on seperate phases. When I turn on one breaker it holds until I turn on the other breaker then they both trip and vise versa.

I was sure this is possible. Now that the sheetrock is up Im thinking I will either need to install Gfis in each outlet all to the line side or will a double pole 20a gfi breaker work and just install new outlets in place of the two gfi outlets?

What is tripping the breakers or the GFCI's? Does each GFCI have an individual hot and white feeding downstream receptacles? You can not use a common neutral on the load side of the GFCI's. If you ran 12-3 in a series to everything you will either need a 2 pole GFCI breaker, 6 individual GFCI receptacles, or redo your cable routing to make it work with 2 GFCI's.
 

iwire

Moderator
Staff member
Location
Massachusetts
Then Dennis said two pole GFCI breakers don't work. I had to check the date on my calender to make sure it wasn't the first yet. When I saw it wasn't I posted "What???" That post, Dennis' post, and bunch of others were deleted for reasons that escape me.

I deleted the posts because they were all focused on correcting a simple mistake that Dennis made, even after he posted that it was a mistake people kept posting about so I deleted those posts.

Now with it all deleted you brought us back to it. :)

So listen up :)

Dennis made a mistake, forget about it and move on.
 

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
I deleted the posts because they were all focused on correcting a simple mistake that Dennis made, even after he posted that it was a mistake people kept posting about so I deleted those posts.

Now with it all deleted you brought us back to it. :)

So listen up :)

Dennis made a mistake, forget about it and move on.

Thats why I posted "had he just woke up", I knew he knew better.:) I was just ribbing Dennis a little, sorry to cause him problems!
 
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ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
I deleted the posts because they were all focused on correcting a simple mistake that Dennis made, even after he posted that it was a mistake people kept posting about so I deleted those posts.

Now with it all deleted you brought us back to it. :)
I'm sorry. I pick at scabs too.
So listen up :)

Dennis made a mistake, forget about it and move on.

Rodger that. I will sit up straight too.;)
 

bth0mas20

Senior Member
Location
Maryland
The breakers are tripping not the gfi's.
I will have to go back tomorrow to see where I have a line to line at. I was starting to think this couldnt work but I feel better that I just have a wiring issue to find.
 

220/221

Senior Member
Location
AZ
How are you related to the electrical industry?
Maintenance electrician
and owner electrical contracting company
Master Electrician

:confused::confused::confused:

It doesn't get much easier than this.

I'm thinking you tied your HR black/red together instead of HR red to jumper black.


Hey...it happens.
 

bth0mas20

Senior Member
Location
Maryland
Thats exactly right I had the black and red from the panel tied together. I was working nights for three weeks at a resturant then running around in the day working houses. Thats what I get for not sleeping. Thanks for all your help.
 
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