Can mwbc feed GFCI receptacles?

[hurk27]

To add some more homework please study the 3 diagrams in post 7 of this thread: http://forums.mikeholt.com/showthread.php?t=135212&p=1296062#post1296062

And 480 has made an excellent post that should clear up your mis-understandings of what we are trying to tell you.

 

[texie]

In my example a 3 pole GFCI breaker would work fine as well.

And so would a 2 pole. My point was I thought he may be thinking 2 seperate 1 pole GFCI breakers.

 

[kwired]

And so would a 2 pole. My point was I thought he may be thinking 2 seperate 1 pole GFCI breakers.

If the title to his OP means anything he was thinking GFCI receptacles, not breakers.

 

[T.M.Haja Sahib]

renosteinke:

I always base my objection about any topic based on another expert's view on it.I based my objection of impossibility of usage of mwbc to feed gfci receptacles on the well-received book'Handbook of Practical Electrical Design by Mc Partlands'.

I am as much a professional as anybody here.

I do not know why you have a such false impression about me.:slaphead:

 

[Ponchik]

I always base my objection about any topic based on another expert's view on it.I based my objection of impossibility of usage of mwbc to feed gfci receptacles on the well-received book'Handbook of Practical Electrical Design by Mc Partlands'. I do not know why you have a such false impression about me.:slaphead:

can you copy and paste the section that says you cant use GFCI with MWBC?

 

[George Stolz]

I based my objection of impossibility of usage of mwbc to feed gfci receptacles on the well-received book'Handbook of Practical Electrical Design by Mc Partlands'.

It appears, based on what you have said about it, to be a gold mine of inaccurate information. Perhaps you could post the text from the book so that we can review it?

Your latest reported post has been noted.

 

[480sparky]

renosteinke:

I always base my objection about any topic based on another expert's view on it.I based my objection of impossibility of usage of mwbc to feed gfci receptacles on the well-received book'Handbook of Practical Electrical Design by Mc Partlands'.

I am as much a professional as anybody here.

I do not know why you have a such false impression about me.:slaphead:

It is entirely possible, safe, and NEC-allowed to use a MWBC to feed GFCI receptacles.

 

[T.M.Haja Sahib]

To add some more homework please study the 3 diagrams in post 7 of this thread: http://forums.mikeholt.com/showthread.php?t=135212&p=1296062#post1296062

And 480 has made an excellent post that should clear up your mis-understandings of what we are trying to tell you.

The bottom most diagram in that is exactly what I mean.You can easily see it is not mwbc:it has two separate neutral wires.

 

[T.M.Haja Sahib]

It is entirely possible, safe, and NEC-allowed to use a MWBC to feed GFCI receptacles.

Please do not think the mwbc stops with the line sides first set of gfci receptacles;it should extend up to the last receptacle to feed them all and in that case it is not possible due to nuisance tripping of gfci.

 

[Dennis Alwon]

In my example a 3 pole GFCI breaker would work fine as well.

Just curious do they make a 3p gfci? Your point is correct at least of a dp gfci and would be if they made a 3p but I have not seen a 3p gfci

 

[hurk27]

The bottom most diagram in that is exactly what I mean.You can easily see it is not mwbc:it has two separate neutral wires.

The NEC considerer's a circuit in how it is fed, not on how the circuit is used at the load end, in both those applications the circuit is a MWBC because it come from the panel from two different phases but share the same neutral, just because they split to two receptacle loads at the end does not change it from being a MWBC, even if you just only had the two GFCI's at the end since the sharing of the neutral on the line side of the GFCI's will not cause the GFCI's to trip, if you study the PDF file I posted you will see why, as you will also see why a two pole GFCI breaker will even allow a MWBC on the load side of the breaker, it done all the time, and has been for years.

Also after you have split into two separate circuits, it no longer meets the definition of a MWBC, but the NEC still treats it as one when applying the rules.

You agree that having two receptacles on a MWBC is still a MWBC, now replace those receptacles with two GFCI's and feed the MWBC to the line side only and you will still have a MWBC but with two GFCI's that will function, but after the GFCI's you can not share the neutral only on the line side, so to run load side receptacles from these GFCI's you must use a separate neutral for each circuit from each GFCI, as in the third diagram that I posted a link too.

Without knowing what was said in that book we can not clear up what your not understanding.

But if you study the PDF and pay attention to the 240 volt two pole description it should clear up what your not seeing, you first have to understand how a GFCI works, without that it will be hard to get you to understand what we are trying to tell you.

 

[charlie b]

Please do not think the mwbc stops with the line sides first set of gfci receptacles. . . .

It is a MWBC as soon as it leaves the panel. Nothing, I say again NOTHING that happens further downstream will change the fact that this is a MWBC. You are simply wrong in your interpretation of what constitutes a MWBC.

. . . and in that case it is not possible due to nuisance tripping of gfci.

There will be no nuisance tripping, if the devices are wired correctly. Your post #9 describes an incorrect wiring method, so there is no reason to believe it would work properly. I have explained this in what I hope was a clear manner. So please either tell me what is wrong about my explanation, or tell me you concede that your previous view was incorrect.

 

[hurk27]

Please do not think the mwbc stops with the line sides first set of gfci receptacles;it should extend up to the last receptacle to feed them all and in that case it is not possible due to nuisance tripping of gfci.

Why do you think the MWBC has to extend to the last receptacle? there is no rule it has to, and doing so will make the GFCI's trip, that is why we can't on this type of circuit.

Being that there is no rule that a MWBC has to run to the last load, then this is a design choice that allows us to use GFCI's on a MWBC, I do not get the reason for this statement, we can design circuits in many different ways, and this is just one of them that we do, and have been doing for years.

 

[al hildenbrand]

The bottom most diagram in that is exactly what I mean.You can easily see it is not mwbc:it has two separate neutral wires.

Please do not think the mwbc stops with the line sides first set of gfci receptacles;it should extend up to the last receptacle to feed them all and in that case it is not possible due to nuisance tripping of gfci.

Below is 480sparky's diagram Sahib refers to.

Sahib, don't use this method if you want a MWBC to run all the way to the last receptacle outlet. Instead, use the method shown in the other diagram with this noteable modification: Install a regular two pole circuit breaker. Install a GFCI receptacle at every receptacle location.

Again, Sahib, in this second diagram directly above these words, Install a regular two pole circuit breaker in place of the GFCI breakers. Install a GFCI receptacle at every receptacle location.

You will have a MWBC all the way to the last receptacle, AND, all of the GFCI receptacles will work perfectly.

 

[al hildenbrand]

Sahib, see? That's what I said to you back in Post # 8.

Bob's diagram shows a Junction Box where the MWBC is spliced to two wire branch circuit extensions.

One doesn't have to do that.

Bring the MWBC in to a receptacle outlet box, use one energized conductor of those in the MWBC to supply the line side "hot" terminal of the GFCI, and use the MWBC neutral to supply the GFCI line side "neutral" terminal.

That's it. The MWBC is not modified.

The MWBC can continue downstream to addition outlets from this receptacle outlet box.

The GFCI is absolutely stable. Any unbalanced neutral currents on the MWBC neutral are NEVER seen by the GFCI sensor.

 

[hurk27]

Sahib here in America all our services are nothing but a large MWFC, that is two hots on opposite phases, with one common neutral, if you could not use a GFCI on a MWBC then they would not work on any service in America, a MWBC is only an extension of the same two hots and common neutral, the trick is the shared neutral is ahead of the single GFCI device (line side) not after (load side)

 

[480sparky]

The bottom most diagram in that is exactly what I mean.You can easily see it is not mwbc:it has two separate neutral wires.

But.... it is still fed by a MWBC.

 

[480sparky]

Please do not think the mwbc stops with the line sides first set of gfci receptacles;it should extend up to the last receptacle to feed them all and in that case it is not possible due to nuisance tripping of gfci.

Where does the Code state that a MWBC MUST continue through the entire length of the circuit?

 

[mivey]

...Again, Sahib, in this second diagram directly above these words, Install a regular two pole circuit breaker in place of the GFCI breakers. Install a GFCI receptacle at every receptacle location.

You will have a MWBC all the way to the last receptacle, AND, all of the GFCI receptacles will work perfectly.

That is about as plain as you can make it and clearly illustrates that this:

A mwbc by definition has shared neutral.So if we try to use gfci receptacles in a mwbc,it will lead to nuisance tripping of gfci's.So my answer to' Can mwbc feed GFCI receptacles?' is no.

Is simply not true.

Also T.M.,
it would not be the first time I have seen mistakes in texts, but I find it hard to believe that McPartland has said the exact same thing in his "Handbook of Practical Electrical Design". He may have said it, but honestly, some of the things you post seem to be confusing at times.

Please post the passage from the book as it may just be a misunderstanding of what the author has said.

Thanks

 

[ActionDave]

In my example a 3 pole GFCI breaker would work fine as well.

I want one of those for Christmas!!