Can mwbc feed GFCI receptacles?

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T.M.Haja Sahib said:
No,sir.I am afraid you missed something.Consider a mwbc 120v/240v circuit feeding two gfci receptacles,each gfci wired to the outer hot conductors,but, per the definition of mwbc,with the neutral on the load side of one gfci connected to the line side of other gfci.If the gfci receptacle with line side connected neutral supplies any load,it would trip the other gfci due to neutral current flow through it.
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T.M.Haja Sahib said:
A true mwbc 120v/240v circuit feeding gfci receptacles should meet the condition in post #9.In that case it can not function due to tripping of gfci.
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Respectfully,

This is wrong.

Again, the GFCI receptacle load side neutral cannot be spliced back to the LINE SIDE neutral. That GFCI, so connected, will trip the instant it is energized.

Respectfully, you must get two physical GFCIs and wire them. Even just one GFCI receptacle will, so connected, will demonstrate the error of your thinking.

While I am an electrical engineer, I am also a working, hands on the tools, electrician. What I am saying is physical GFCI receptacle beginners knowledge. One only has to hook up a physical GFCI like you describe once, and you will never do it deliberately again . . .
 
charlie b said:
It is a MWBC because that is what it was when it left the panel. What you do with the wires after they leave the panel will not change the character of the circuit. For example, when you get to the last outlet (i.e., furthest or most remote from the panel), all you will have is one hot conductor and one neutral (plus the EGC). You no longer have multiple hot conductors. If a person opened that outlet box and looked inside, they would only see these three wires, and think this was just a standard, single phase circuit. It is not, and the person would have to look further upstream to notice that multiple hot conductors shared a neutral when they left the panel, and continued to share the neutral up to the first junction box or outlet box they entered. Nothing that happens downstream from that point can change the fact that the circuit is a MWBC.
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But al hildenbrand says (post#19)after gfci's,the circuit is no longer MWBC.
 
al hildenbrand said:
Respectfully,

This is wrong.

Again, the GFCI receptacle load side neutral cannot be spliced back to the LINE SIDE neutral. That GFCI, so connected, will trip the instant it is energized.

Respectfully, you must get two physical GFCIs and wire them. Even just one GFCI receptacle will, so connected, will demonstrate the error of your thinking.

While I am an electrical engineer, I am also a working, hands on the tools, electrician. What I am saying is physical GFCI receptacle beginners knowledge. One only has to hook up a physical GFCI like you describe once, and you will never do it deliberately again . . .
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I am also saying the same thing and so a 120v/240v mwbc can not feed gfci receptacle because of tripping of gfci.
 
Is it possible that our friend Mr. Sahib is thinking of a MWBC being fed from 2 actual GFCI breakers as opposed to GFCI receps. He may not be aware that we typically use a GFCI recep and not a GFCI breaker as in the old days.
 
T.M.Haja Sahib said:
I am also saying the same thing and so a 120v/240v mwbc can not feed gfci receptacle because of tripping of gfci.
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Yes it can. One circuit is connected to one GFCI receptacle. One circuit is connected to the other. Done. End of story. A MWBC is brought to a box and terminated in that fashion wil not have a problem.
 
T.M.Haja Sahib said:
I am also saying the same thing and so a 120v/240v mwbc can not feed gfci receptacle because of tripping of gfci.
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Very humbly and respectfully,

NO. You are not saying the same thing.

You are missing something in your thinking. We're showing it to you, but you are still missing what we're saying.
 
T.M.Haja Sahib said:
Then the whole circuit is not a mwbc.
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No one is saying that it is.

Whether the whole circuit is a MWBC is not part of your OP question.

Your contention that the GFCIs will trip is wrong, unless one deliberately wires the GFCIs incorrectly as you describe in your Post #9.
 
T.M.Haja Sahib said:
A true mwbc 120v/240v circuit feeding gfci receptacles should meet the condition in post #9. In that case it cannot function due to tripping of gfci.
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Let?s go back to your post #9:
T.M.Haja Sahib said:
Consider a mwbc 120v/240v circuit feeding two gfci receptacles, each gfci wired to the outer hot conductors, but, per the definition of mwbc,with the neutral on the load side of one gfci connected to the line side of other gfci. If the gfci receptacle with line side connected neutral supplies any load, it would trip the other gfci due to neutral current flow through it.
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You are not describing the correct way to wire the receptacles, and that is why you are not understanding the situation. To be specific, the second receptacle is not, in fact, on the ?load side? of the first.

When you bring the three wires into that first GFCI receptacle outlet?s box, what happens is you cut one hot wire and the neutral wire, and leave the other hot wire uncut. You then cut a six inch or so length of the black wire and another length of white wire. You then put the two ends of the hot wire and one end of the short black wire into a wire nut, and twist them together. You connect the other end of the short length of black wire to the line side of the GFCI receptacle. You do the same thing with the white wires. The wires that leave this box and head downstream to the next box consist of the first hot wire (i.e., that had been cut and reconnected), the neutral wire (i.e., that had also been cut and reconnected), and the other hot wire (i.e., the one that had not been cut).

Current coming into that box on the hot conductor will split into two paths, with some going into the receptacle (i.e., into whatever is plugged into that receptacle) and the rest going on to the next outlet downstream. Current returning towards the panel from outlets downstream will enter that same box, but will not be going through the GFCI receptacle itself. Rather, it will go into the point where three wires are connected by the wire nut, and will bypass the receptacle, and go directly upstream to the panel. Therefore, loads that are plugged into the second GFCI receptacle will not cause a trip of the first GFCI receptacle.
 
T.M.Haja Sahib said:
Then the whole circuit is not a mwbc.
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The circuit is a MWBC. Portions of it may only have one hot and one neutral, and those portions do not share the "multi-wire" characteristics of the circuit as a whole. But the circuit itself is multi-wire.
 
TM, look at Iwire's diagram in post 5. This is a very common setup in residential wiring

using 14-3 w/g or 12-3 w/g. You can take your MWBC to the first box & put a GFCI on one

hot leg & have the other leg serve the microwave. Abouslety no problems. Iwire's diagram

has three hots, we would only have two hots
 
Jljohnson said:
Haja, you are not seeing the circuit the same as the others, maybe this will help you understand what they are saying.
a) The MWBC feeds ONLY the line side of the GFI receptacles
b) On the load side of the GFI receptacle, the N. conductor can no longer be shared with the rest of the MWBC unless your protection is coming from multi-pole GFI breaker, not being provided by a GFI receptacle.
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Load side conductors of any GFCI have to be excluded from interconnecting with ANY other wiring that is not part of load side of same GFCI. Does not matter if it is a 2 wire circuit or a 1000 wire MWBC.

This is no different than putting a light switch in line 1 of a MWBC and connecting the light to the other terminal of the switch. If you would tie the switched lead back to line 1 you will not get the desired results from the switch, you have to keep it separated for it to function as desired. GFCI is a switch that has more than simple mechanical operation to make it function. A multipole switch could be installed in place of a GFCI (not for GFCI protection obviously, but for showing the logic of the circuit only) and you you still have the same circuit layout. Connect a line side neutral to the load side neutral and you bypassed one pole of the switch and no longer have the same circuit layout.
 
Let me extrapolate on this part of my previous post:
charlie b said:
To be specific, the second receptacle is not, in fact, on the “load side” of the first.
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In my kitchen, I have three circuits serving receptacles on the countertop. They are separate circuits, and do not share neutrals. For each of the three circuits, I have two wires (one hot and one neutral) going from the panel to an outlet box. Inside that box is a GFCI receptacle, and the two wires are connected to its line side. From the “load side” of the GFCI receptacle, I have a hot wire and a neutral wire going to a second outlet box a couple feet away. These wires land on a standard (i.e., not GFCI) receptacle. When I plug something into the second receptacle, all of its current also flows through the GFCI receptacle upstream.

Now let me plug an appliance into the GFCI receptacle and another into the standard receptacle on its load side, and turn both appliances on. If I were to push the test button on the GFCI receptacle, then both appliances would stop running. This is what is meant by saying the second receptacle is on the load side of the first.

In your post #9, you incorrectly state that the second receptacle is on the load side of the first. That is not correct, because you are bringing a separate power source to the second. For the second receptacle to be on the load side of the first receptacle, then, (1) All of the current going to the second receptacle will first have to go through the first receptacle, and (2) All of the current returning from the second receptacle will have to go back through the first receptacle. That is not how you described the wiring in post 9, and that is why your description of the wiring was incorrect.
 
I don't often make posts that I expect to see deleted ... but I'll not be upset if this one goes away. I just don't know how else to put my thoughts forward ....

I weary of the OP, and his tortuous twisting of words and concepts. Someday, someone who does not know better will follow his advice, and get themselves hurt.

Sahib isn't here to learn and share ... he's here to rule and preach.

Please ban the troll.
 
Given, that as I type, it is approximately 1 AM Friday morning in Chennai, India, I suspect that T.M. Haja Sahib has retired for the night. :sleep:
 
The only thing that I could add to this thread is that to prove you can always on the line side of a GFCI share the neutral and the proof is simple, every service panel shares the neutral ahead of any or all GFCI's on that service, this is because it is done on the line side, after the GFCI neutrals can not be shared so the load side neutrals must be kept separate, two or three pole GFCI breakers can again share the neutral because all the circuit conductors are running through the sensing coil, to understand how a GFCI works Please see this atachment:
It is a PDF file to which you will need a PDF reader, but please read it and study it so you can learn how a GFCI functions.
 

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texie said:
Is it possible that our friend Mr. Sahib is thinking of a MWBC being fed from 2 actual GFCI breakers as opposed to GFCI receps. He may not be aware that we typically use a GFCI recep and not a GFCI breaker as in the old days.
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In my example a 3 pole GFCI breaker would work fine as well.
 
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