GFCI on Multiwire Circuits

[360Youth]

Single-pole GFI breakers will not work in a multiwire circuit application, correct? (I would have to loop the load side neutral from breaker to breaker.) Someone suggested that if they were on the same phase it might work, but wouldn't that affect the neutral load? I do very little multiwire circuits, so forgive my rustiness on the subject. Thanks.

 

[iwire]

Nope not going to work.

 

[augie47]

"someone " is wrong
Remember the GFCI measures the current on both conductors so any other "path" will result in them not working.
You can use a 2 pole GFCI on a MWBC.

 

[Dennis Alwon]

Single-pole GFI breakers will not work in a multiwire circuit application, correct? (I would have to loop the load side neutral from breaker to breaker.) Someone suggested that if they were on the same phase it might work, but wouldn't that affect the neutral load? I do very little multiwire circuits, so forgive my rustiness on the subject. Thanks.

As Bob stated it won't work unless you buy a dp gfci breaker. This will work. You could also possibly break the circuit downstream with GFCI Recep.

You cannot use the same phase in a MWBC simply because you could not comply with 210.4(B) in the 2008 NEC

 

[360Youth]

Thank-you, gentlemen. That is what I thought.

 

[360Youth]

You cannot use the same phase in a MWBC simply because you could not comply with 210.4(B) in the 2008 NEC

This is a stretch, but it got me thinking, could a multiwire be used on a tandem breaker if there is one that handle-ties together? Never occured to me until your statement so I just thought I would throw it out there.

 

[mcclary's electrical]

This is a stretch, but it got me thinking, could a multiwire be used on a tandem breaker if there is one that handle-ties together? Never occured to me until your statement so I just thought I would throw it out there.

Only if you want to FRY your neutral wire

 

[1793]

This is a stretch, but it got me thinking, could a multiwire be used on a tandem breaker if there is one that handle-ties together? Never occured to me until your statement so I just thought I would throw it out there.

I would say "no". With a tandem you would still be on the same phase, leg. If I read you correctly.

 

[Dennis Alwon]

This is a stretch, but it got me thinking, could a multiwire be used on a tandem breaker if there is one that handle-ties together? Never occured to me until your statement so I just thought I would throw it out there.

This has been tossed around and I believe many here believe if the neutral is size appropriately then it would not matter. The disco would be the hard thing to comply with.

 

[360Youth]

Only if you want to FRY your neutral wire

Yes, that gets back to my neutral point in my original post. But that could also be accounted for in wire sizing. None of this I agree with in practicality or intent, but I felt an itch to make an exagerated NEC wording point that we so often see here.

 

[480sparky]

I would say "no". With a tandem you would still be on the same phase, leg. If I read you correctly.

Not always. There are some tandems that can be used on opposite phases. The old Challengers come to mind. You had to order 'left hand' and 'right hand'.

GE half-size breakers could also be places side by side on opposite phases.

 

[1793]

Not always. There are some tandems that can be used on opposite phases. The old Challengers come to mind. You had to order 'left hand' and 'right hand'.

GE half-size breakers could also be places side by side on opposite phases.

Good call. I forget about some these configurations. I think FPE makes a breaker like this too.

 

[360Youth]

Not always. There are some tandems that can be used on opposite phases. The old Challengers come to mind. You had to order 'left hand' and 'right hand'.

GE half-size breakers could also be places side by side on opposite phases.

Yea, but my tandem question was with the intent of the multiwire coming off the same phase. It was suggested that the multiwire had to be on separate phases in order to disconnect both ungrounded at the same time. I just threw out for arguement sake, could it be done with a tandem (on the same phase) with the handles tied together and still meet code? Providing neutral sizing was taken into consideration.

 

[Dennis Alwon]

Yea, but my tandem question was with the intent of the multiwire coming off the same phase. It was suggested that the multiwire had to be on separate phases in order to disconnect both ungrounded at the same time. I just threw out for arguement sake, could it be done with a tandem (on the same phase) with the handles tied together and still meet code? Providing neutral sizing was taken into consideration.

Interesting point. I believe they make handle ties for the thin (wafer) breakers but I am not sure.

 

[LarryFine]

Someone suggested that if they were on the same phase it might work, but wouldn't that affect the neutral load?

Yes, but, if the loads permit, you could convert these two circuits into a single one by tying both ungroundeds together and landing them on a SP GFCI breaker.

 

[sameguy]

You could changr the service or add a sub, then have room and make more $$$

 

[don_resqcapt19]

Yea, but my tandem question was with the intent of the multiwire coming off the same phase. It was suggested that the multiwire had to be on separate phases in order to disconnect both ungrounded at the same time. I just threw out for arguement sake, could it be done with a tandem (on the same phase) with the handles tied together and still meet code? Providing neutral sizing was taken into consideration.

By definition is it not a multiwire circuit if both ungrounded conductors are connected to the same leg.

Branch Circuit, Multiwire. A branch circuit that 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.

I think the use of more than one ungrounded conductor of the same leg or phase is a "common neutral" circuit.

 

[jaylectricity]

You could changr the service or add a sub, then have room and make more $$$

How would that help? The issue is not having too few spaces in the panel.

By definition is it not a multiwire circuit if both ungrounded conductors are connected to the same leg.

I think the use of more than one ungrounded conductor of the same leg or phase is a "common neutral" circuit.

I think he was suggesting that if the OP really needs to put one of those circuits on a GFI breaker, he could just combine the circuits into one circuit if the load would allow.

 

[360Youth]

By definition is it not a multiwire circuit if both ungrounded conductors are connected to the same leg.

True, I did not think of that when I started my tandem speculation.

 

[360Youth]

Too much load for combining circuits.