mbc gfi's

[GerryB]

Can you pigtail the neutral and put two GFI's on a multi wire branch circuit? Black to one gfi and red to the other. Then from that 2-gang box 3 wire to another 2-gang with two receptacles one off of each load side gfi, again sharing the neutral. I think I had a problem with this one time.

 

[ActionDave]

No, you cannot do that. You need to take a separate neutral to each plug after the load side of the GFCIs.

 

[iwire]

I agree with the man of action.

If you share the neutral with anything on the load side of a GFCI it will trip all the time.

 

[ActionDave]

And I thank the man who wires for agreeing.

 

[GerryB]

OK so the first box is ok? 12-3, 2 gfi's in the 2 gang box. But from there if you had to protect downstream you would need to run 12-2 from each gfi. The problem I had once was a 12-3 to the counter top (duplex gfi) and then one of those ckts (red) was for the dw. I was also feeding through the gfi to another counter outlet. I think I had the dw neutral off the load instead of the line. As soon as you turned on the dw switch the gfi popped.

 

[kwired]

A little understanding of how a GFCI works will make it easier to understand.

A GFCI has all the protected conductors pass through a current transformer. This can be just two conductors for a typical 120 volt circuit or both "hots" and the neutral for 120/240 multiwire circuits. The basic idea is any current that leaves the load side L1 terminal has to come back on either load side L2 or load side neutral, if not then voltage is developed in the current transformer and if it above the 4-6 mA level required for class A GFCI devices it will initiate the trip mechanism and open the circuit. You can not combine two separate devices as each has it's own current transformer and the portion of load that finds a path through the other device will cause trip every time - probably will trip both devices nearly every time.

 

[dmxtothemax]

For this idea to work
You need to ensure that
All load side neutrals are
Connectted only to the gfi
Load side neutral.
Then the neutrals can be
Pigtailed only on the line
Side of the gfi.
Then it will work.
But if any of the load side
Neutrals find a way back to
Main neutral via any path
Other than the gfi then it
Will not work !

 

[kwired]

For this idea to work
You need to ensure that
All load side neutrals are
Connectted only to the gfi
Load side neutral.
Then the neutrals can be
Pigtailed only on the line
Side of the gfi.
Then it will work.
But if any of the load side
Neutrals find a way back to
Main neutral via any path
Other than the gfi then it
Will not work !

It will not work period. You current that leaves one breaker has potential paths back through the other breaker, this will throw the balance in the sensing CT off for every load over 4-6 mA, not to mention they will trip with no load in the first place because they have circuitry that injects a signal to detect neutral to ground faults, that injected signal will find a path to the other circuit and cause it to trip even when there is no load. You have to use a two pole GFCI with neutral terminals for multiwire circuits as all three wires of the circuit will pass through the monitoring CT in such devices.

 

[JFletcher]

OK so the first box is ok?

Yes.

12-3, 2 gfi's in the 2 gang box. But from there if you had to protect downstream you would need to run 12-2 from each gfi.

Yes.

A 2p GFCI breaker would also work on a MWBC, tho the cost is pretty high compared to 2 GFCI receptacles.