Multi- wire branch circuit feeding GFCIs

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Jpflex

Jpflex

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Electrician commercial and residential
I have a 12-3 multi wire Romex with two hots and a shared neutral and a ground. The NM Cable red wire goes to one 20 ampere breaker ant main panel and the same cables black wire to a different 20 ampere breaker. Red and black go to a separate GFCI Hot terminal on their line side terminals

However there is only one neutral out of multi wire branch circuit NM cable so the single neutral FROM PANEL NEUTRAL BUS goes to first GFCI neutral line side

But do I pigtail this neutral from line side at first GFCI and connect to the next GFCI down stream and on another circuit to its neutral terminal on line side? load side seems wrong and previous install had two hots and one neutral for two circuits with one GFCI which had stopped working

I’m thinking any additional receptacles on load side of GFCIs will force me to have to add at least one more neutral in emt conduit downstream of GFCIs for load side terminals?

Normally separate circuits must have their own neutral in NEC 300 except for multi wire branch circuits I believe?

GFCI tripped but I will look into this tomorrow
 
You must ALWAYS pigtail the neutral on a MWBC. At the 1st box, pigtail the neutral, the "tail" going to the neutral, and the rest going to the next box. If they are GFCI receptacles, the neutral (and hot) would both go on the line side of each GFCI.
 
A normal 120V GFCI can be fed _from_ a MWBC, but it cannot feed _to_ a MWBC. So you must pigtail the neutral feeding the line side of the receptacles. Anything fed from the load side of the GFCI receptacles must have completely separate neutrals.

-Jon
 
Jpflex said:
But do I pigtail this neutral from line side at first GFCI and connect to the next GFCI down stream and on another circuit to its neutral terminal on line side? . . .
I’m thinking any additional receptacles on load side of GFCIs will force me to have to add at least one more neutral in emt conduit downstream of GFCIs for load side terminals?
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Yes and yes, assuming you just have two GFCIs total (one for red, one for black) and each protects downstream non-GFCI receptacles.

If every receptacle is a GFCI, then you can ignore all the load terminals and wire everything as if they were regular receptacles.

Cheers, Wayne
 
winnie said:
A normal 120V GFCI can be fed _from_ a MWBC, but it cannot feed _to_ a MWBC. So you must pigtail the neutral feeding the line side of the receptacles. Anything fed from the load side of the GFCI receptacles must have completely separate neutrals.

-Jon
Click to expand...
I think this is why I got tripping
 
Ok so if I take out the multi wire cable and just put in two 12-2 NM cables from breaker to first and second GFCIs I’ll have a designated neutral for each GFCI on their line terminals

Then I can add another neutral for load side of GFCIs so they each have their own neutral

It’s a lot of work but having just 1 neutral for two GFCIs ON TWO DIFFERENT CIRCUITS, and two standard receptacles down stream or 1 receptacle on each load side of GFCI just seems to complicate this

Plus would it be possible for GFCI to trip if both GFCI share a neutral caused by an ampere imbalance between circuits sharing a neutral when loads are added to each circuit?
 
Jpflex said:
Ok so if I take out the multi wire cable and just put in two 12-2 NM cables from breaker to first and second GFCIs I’ll have a designated neutral for each GFCI on their line terminals
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No, you can keep the 3-wire MWBC. At the first outlet, split the neutral, and wire everything from that point as two 2-wire circuits, using only line terminals. You can feed additional receptacles from each GFCI receptacle's load terminals; just keep the load conductors separate.

You can also continue the MWBC as a 3-wire circuit or two 2-wire circuits by connecting to the line-side wires at or before the line terminals. Only 2-wire circuits can be extended from the load terminals. Here are two example drawings of the same thing:

1683769491396.png 1683769510697.png
 
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Thanks. Looks good and simple fix. However does NEC require a special 2 pole breaker with tie and for this set up if so would it give me the desired 40 amperes (2x20) that I would have got from 2 single pole 20 ampere breakers?

What would happen if I just left two single pole breakers per line on mwbc?
 
Jpflex said:
Thanks. Looks good and simple fix. However does NEC require a special 2 pole breaker with tie and for this set up if so would it give me the desired 40 amperes (2x20) that I would have got from 2 single pole 20 ampere breakers?

What would happen if I just left two single pole breakers per line on mwbc?
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Well being that we ran MWBCs back when we used fuses, (and I've never figured out how to handle tie fuses), really nothing. But you will be in violation oF the NEC
 
Jpflex said:
Thanks. Looks good and simple fix. However does NEC require a special 2 pole breaker with tie and for this set up if so would it give me the desired 40 amperes (2x20) that I would have got from 2 single pole 20 ampere breakers?
Click to expand...
First of all, 2 x 20a 120v circuits is 20a at 240v, not 40a at 120v.

Yes, for manual disconnecting, because of the shared neutral, the handles must be joined.

Not a special 2p breaker, a standard 2p breaker, or a handle tie.

What would happen if I just left two single pole breakers per line on mwbc?
Click to expand...
We would call it one breaker per line ("phase"), unless you're calling an MWBC one line.

The problem with independent 1p breakers is that they could accidentally be placed on the same line.
 
Another option is to get a 2-pole 20a GFCI breaker. That will provide GF protection across both circuits, takes care of the handle tie, and eliminates the need for two or more GFCI outlets (which depending on their location to the first device may be helpful, e.g. dishwasher/disposal/sump).
1683815621041.png
 
LarryFine said:
First of all, 2 x 20a 120v circuits is 20a at 240v, not 40a at 120v.

Yes, for manual disconnecting, because of the shared neutral, the handles must be joined.

Not a special 2p breaker, a standard 2p breaker, or a handle tie.


We would call it one breaker per line ("phase"), unless you're calling an MWBC one line.

The problem with independent 1p breakers is that they could accidentally be placed on the same line.
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Yes I recall now that multi wire branch circuits establish 240 volts between “2?” Loads with neutral connecting middle of loads instead of having 120 per single load.

However if a second load were not on how do you limit the ampacity of this set up for a single load impedance or resistance?
 
Jpflex said:
However if a second load were not on how do you limit the ampacity of this set up for a single load impedance or resistance?
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I'm not sure I understand the question. The two circuits behave as independent circuits.

See if this helps:

Understanding the Neutral Conductor

Dennis, here's a really basic lesson, and we'll start with direct current, because the fact that we use alternating current is not relevant to the basics: Picture a battery, like you'd find two of in a flashlight. You have a terminal at each end, with a difference in potential of 1.5 volts...
forums.mikeholt.com
 
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