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T.M.Haja Sahib
Guest
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.
- Status
- Location
- Massachusetts
And you would be 100% incorrect.
Next question please.
Next question please.
T
T.M.Haja Sahib
Guest
You mean it is possible without any modification to mwbc?
roger3829
Senior Member
- Location
- Torrington, CT
Absolutely
- Location
- Massachusetts
Absolutely.
Done all the time by yours truly and 1000s of others often.
I can supply large numbers of GFCI receptacles from MWBCs without any problem or modifications.
Perhaps you should draw the circuit out and see if you can point to a reason why it would not work?
Heck I will even help you out, any of the receptacles in this crude drawing could be GFCIs. Or The breaker could be a GFCI breaker and protect all the receptacles from one point.
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al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
A GFCI receptacle only has one terminal for the line side energized conductor. Therefore, one can only connect ONE of the energized conductors of a MWBC to a GFCI at a time. The only neutral current returning from any load downstream of the GFCI will be the current that passes through the GFCI on the energized conductor, that is, unless there is a circuit fault of some sort.
QED.
The answer to the OP is YES.
T
T.M.Haja Sahib
Guest
Absolutely.
Done all the time by yours truly and 1000s of others often.
I can supply large numbers of GFCI receptacles from MWBCs without any problem or modifications.
Perhaps you should draw the circuit out and see if you can point to a reason why it would not work?
Heck I will even help you out, any of the receptacles in this crude drawing could be GFCIs. Or The breaker could be a GFCI breaker and protect all the receptacles from one point.
Okay.It is for 3w+neutral circuit.What about 120v/240v 3 wire single phase circuit?
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
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.
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T
T.M.Haja Sahib
Guest
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.
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.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Respectfully,
This one is obvious. I don't know how to get you to "see" what you are not "seeing" except to suggest, very respectfully, that you should take two physical GFCI receptacles and connect them just as you describe to a 120 / 240 Volt MWBC.
The sensor in each GFCI receptacle only "sees" the neutral current returning from the load that is plugged into it (the load downstream from the GFCI receptacle). The GFCI receptacle sensor CANNOT "see" either the MWBC neutral current or the neutral current in the other GFCI receptacle.
T
T.M.Haja Sahib
Guest
Then it can not be mwbc, See 'the shared neutral' in the definition of mwbc.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
This is your error,
The line side GFCI receptacle neutral terminal of each GFCI receptacle are BOTH connected to the MWBC neutral.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
The load side neutral of a GFCI receptacle is never connected back to the line neutral, other wise, that GFCI receptacle will always trip the instant it is energized.
It most certainly is a MWBC. The grounded conductor is shared with the respective ungrounded conductors when it leaves the panel, thus it is a MWBC by NEC definition in article 100. Where are you getting the definition that you refer to in your post?
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
You are correct that the load side neutral is not shared.
That is not the question in your OP.
Whether the GFCI load side neutral is shared, or not, has nothing to do with the OP question.
T
T.M.Haja Sahib
Guest
Then how can we say it is a mwbc,because separate neutral wires are taken to the line side of each gfci and separate neutral wires should be taken on the load sides also?
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
The LOAD SIDE of a standard GFCI receptalcle is supplied by one hot and one neutral.
The LOAD SIDE of a standard GFCI receptacle is not a MWBC.
The LOAD SIDE of a standard GFCI receptacle is not a MWBC.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
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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