Tagged for multiwire branch circuit

kwired

Electron manager
Location
NE Nebraska
Art 100 definitions:

Branch Circuit. The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s)
Branch Circuit, Multiwire. A branch circuit that consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system.
Where does it say a MWBC becomes two separate circuits after it effectively splits into two separate circuits? The whole thing is still one (multiwire) branch circuit.

Service and feeders have nothing to do with these definitions.
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
Where does it say a MWBC becomes two separate circuits after it effectively splits into two separate circuits? The whole thing is still one (multiwire) branch circuit.



It doesn't say it becomes two separate circuits, it says it is no longer a multiwire branch circuit. Branch circuit conductors with only one ungrounded and one grounded conductor does NOT meet the definition of "Branch Circuit, Multiwire."
 
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kwired

Electron manager
Location
NE Nebraska
It doesn't say it becomes two separate circuits
I can agree with that

it says it is no longer a multiwire branch circuit.
Where does it say this. It is still the same branch circuit which happens to be a multiwire circuit, it is no longer the multiwire portion of the circuit though, but it also doesn't define an end of the multiwire branch circuit so one could easily say the entire thing is the multwire branch circuit.

Branch circuit conductors with only one ungrounded and one grounded conductor does NOT meet the definition of "Branch Circuit, Multiwire."
Agree. Portions of this circuit have more than that though, so again where does the "multiwire" portion of it end, or does it end?

I agree with the logic here and have wired things that way myself, but that doesn't mean I was right to do so if you interpret the wording pretty strictly as is written.
 

GoldDigger

Moderator
Staff member
It is still the same branch circuit which happens to be a multiwire circuit, it is no longer the multiwire portion of the circuit though, but it also doesn't define an end of the multiwire branch circuit so one could easily say the entire thing is the multwire branch circuit.
[...]
Agree. Portions of this circuit have more than that though, so again where does the "multiwire" portion of it end, or does it end?
The MWBC must start at the connection to the OCPD, and goes as far as it goes, keeping the same status.
Otherwise we would have things like a dedicated receptacle circuit being a valid description of the wiring between the last and second to last outlet in the run. (Assuming the last outlet is the receptacle in question.)
And if we wire up three home runs from three motors back to one OCPD is it no longer a multiple motor circuit?
Contrived, contorted and convoluted examples to be sure, but sometimes that kind of exercise is helpful. :)
 

crtemp

Senior Member
Location
Wa state
Though that is what is logical it is not worded properly to interpret that way.

I'll bet you used either two pole or handle ties, and not both.

Where does it end? Where does it turn into two circuits? AFAIK the entire circuit is a single MWBC, including both "two wire" ends of the circuit.

Again logic says once you separate into the equivalent of two circuits.... but the wording in the NEC doesn't match that logic.

I did not double check NEC before posting so fire away with disagreement, but IIRC this has been debated here before and has been mentioned that if you go strictly by the words in the NEC, the entire MWBC is really supposed to have the neutrals "pigtailed".

I did did use two pole breakers with handle ties. I argued with the inspector for 25 minutes this morning and he finally saw it my way and let it go!
 

GoldDigger

Moderator
Staff member
I did use two pole breakers with handle ties. I argued with the inspector for 25 minutes this morning and he finally saw it my way and let it go!
Was it worth the 25 minutes? I guess you expect the situation will come up a lot?
IMHO you were lucky that the inspector was persuaded by arguments of reason and safety when the exact words of the Code did not support your position. :happyyes:
 

crtemp

Senior Member
Location
Wa state
Was it worth the 25 minutes? I guess you expect the situation will come up a lot?
IMHO you were lucky that the inspector was persuaded by arguments of reason and safety when the exact words of the Code did not support your position. :happyyes:
When the job is over an hour away it was defiantly worth 25 minutes to me. I don't understand why an inspector would tag this anyway when he knows it's being installed in a safe manner. It seems like some inspectors will tag for stuff they know is safe just to be a-holes. Like a "ha ha I got you" type of thing.
 

crtemp

Senior Member
Location
Wa state
Thanks to everyone who agreed with me. I think this is an extremely vague code in my opinion and is left up to interpretation. I don't think there is a safety issue at all with what I'm doing. Is anyone thinking it is unsafe, or just a wording issue?
 

hurk27

Senior Member
Ahhh, but in others interpretation of the "words of the code" the inspector was wrong .

Roger
This topic brought to mind feeding a garage with MWBC, I think with just the definition of a MWBC alone tells me the circuit stops being a MWBC when it no longer has two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit.

Very simply if that part of the circuit doesn't meet the definition of a MWBC then it is not a MWBC.

Look at doing wire counts in box's can you still claim the neutral only carries the imbalance current and not count it after the split? I don't think so:happyno:

My thought is that once the reason or hazard for the pigtail requirement doesn't exist anymore then the rule doesn't apply anymore.

Actually since they introduce the rule of handle ties to MWBC's this rule could go away although I would keep doing it just because I know wires do loose connections at receptacles and I wouldn't want to fry someones expensive equipment, but that is just my thought.
 

hurk27

Senior Member
Thanks to everyone who agreed with me. I think this is an extremely vague code in my opinion and is left up to interpretation. I don't think there is a safety issue at all with what I'm doing. Is anyone thinking it is unsafe, or just a wording issue?
I don't think anyone was arguing that they way you did it was a hazard, just how the thought of where a MWBC ends if it does was the problem, we all know what happens when you loose a neutral connection on a MWBC and loosing one at a receptacle can be a fire hazard when equipment even a lamp is exposed to over voltage, but since you did pig tail the split from the MWBC, the hazard is removed for all intent of the NEC goes, at least in my mine.

Myself I pigtail all my recepts anyway because it makes finding a lost connection much easier after a homeowner used a space heater for a long time, they seem to find the weak spot in any circuit:happyyes:

After knowing that a space heater will be used at a certain receptacle not only will I pig tail the wires, when I connect it to the receptacle I will "S" loop it around both screws giving it more connection area, never had one go bad after doing this, but thats another thread, glad you were able to get the inspector to see the light, not all inspectors are bad, we have many around here who are just wanting to learn as we are and I have made good friends with many as they call me all the time when they have a code question
 

kwired

Electron manager
Location
NE Nebraska
I did did use two pole breakers with handle ties. I argued with the inspector for 25 minutes this morning and he finally saw it my way and let it go!
Two pole breakers already have handles tied together, you do not install a handle tie on those, if you did you would be tieing it to an additional breaker.

Thanks to everyone who agreed with me. I think this is an extremely vague code in my opinion and is left up to interpretation. I don't think there is a safety issue at all with what I'm doing. Is anyone thinking it is unsafe, or just a wording issue?
I have no safety issue with what you did, just a potential wording conflict with applicable code.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
Not sure we are on the same page. Here is an example of what I did. I pulled a 12-3 to the refrigerator plug. The black of the 3 wire does the kitchen small appliance circuit and the red does the microhood circuit. The box has the following wires in it. A 12-3 home run. A 12-2 going to the microhood. And a 12-2 continuing on to the next kitchen plug. In the refer plug box I have the neutrals from the 12-3 and the neutral from the 12-2 going to the micro pigtailed down to one wire that gets wired on the plug. The 12-2 that is feeding the other kitchen plugs is not pigtailed all. If the plug gets taken off of the refer it will have no effect on the neutral of the microwave.
As I read this you have 2 neutrals on the receptacle for the refrigerator. Those neutrals are the one going to the small appliance branch circuit as well as the pigtail from the multiwire branch circuit and the microwave.

As I see it that is compliant although I would have pig tailed all the neutrals. How is this any different then any two wire circuit where the neutrals are connected thru the receptacle?

I agree with the OP.

This section below does not come into play because there isn't a multiwire branch circuit on the duplex.

300.13(B) Device Removal. In multiwire branch circuits, the continuity of a grounded conductor shall not depend on device connections such as lampholders, receptacles, and so forth, where the removal of such devices would interrupt the continuity.
 

kwired

Electron manager
Location
NE Nebraska
As I read this you have 2 neutrals on the receptacle for the refrigerator. Those neutrals are the one going to the small appliance branch circuit as well as the pigtail from the multiwire branch circuit and the microwave.

As I see it that is compliant although I would have pig tailed all the neutrals. How is this any different then any two wire circuit where the neutrals are connected thru the receptacle?

I agree with the OP.

This section below does not come into play because there isn't a multiwire branch circuit on the duplex.
Yes, but the debate here is whether or not the entire circuit is the multiwire branch circuit, which technically would mean you still must pigtail the neutral even after discontinuing one of the ungrounded conductors in the run. As things are worded it can certainly be interpreted to mean just that. I do agree the intent is probably met as long as you can not interrupt the neutral that is still common to more than one ungrounded conductor by removal of a device.
 

GoldDigger

Moderator
Staff member
I will end the debate.

The entire circuit is not a MWBC.

Next question .....:cool:
OK, following one perfectly reasonable interpretation of written English grammar and usage, you have just asserted that none of the circuit is an MWBC. (See, it did not end the blather, even if it ends the debate.):roll:
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
I will end the debate.

The entire circuit is not a MWBC.

Next question .....:cool:

I agree. There is no way that the intent was to not allow the situation the op stated. It is no different then a standard two wire circuit at that point and it ties to a multiwire branch circuit. We can play name games all day but the fact is the op's situation is not a safety issue.
 

mcgroh

Member
Compliant if - - -

Compliant if - - -

Not sure we are on the same page. Here is an example of what I did. I pulled a 12-3 to the refrigerator plug. The black of the 3 wire does the kitchen small appliance circuit and the red does the microhood circuit. The box has the following wires in it. A 12-3 home run. A 12-2 going to the microhood. And a 12-2 continuing on to the next kitchen plug. In the refer plug box I have the neutrals from the 12-3 and the neutral from the 12-2 going to the micro pigtailed down to one wire that gets wired on the plug. The 12-2 that is feeding the other kitchen plugs is not pigtailed all. If the plug gets taken off of the refer it will have no effect on the neutral of the microwave.
The essence of the code requirement is that the neutral path back not be interrupted. As I understand it you combine the neutral from the 12-3 with the one going to the microhood and another pigtail which goes to the LINE side of the duplex (along with the black from the 12-3). On the LOAD side of the duplex you have the 12-2 going to the downstream receptacles on the Kitchen Small Appliance Circuit (SAC). In this case if the duplex is removed or fails, the neutral for the microhood WHICH SHARES THE NEUTRAL WITH THE SAC will not be effected and there is no risk of a line to line load. As I see it, and if I understand what you are doing, this IS compliant.

Side Bar: I see MANY mistakes in my property intersections with MWBC. In my opinion, more electricians than not are confused by these. I frequently see issues with GFCI Protection in the newer installations (get a two-pole GFCI Breaker and you will have no issues if installed correctly. Sure, a bit more expensive sure, BUT it does the job so well!). The next biggest issue I see, particularly with older installations (prior to the handle tie requirement) is the breakers coming off the same bus (phase). Again the theory is MWBC share a neutral with oppositely phased current so that w/ a max load on each circuit (red and black in this case) they will cancel each other and no load will exist on the neutral. If max load from one phase is doubled (red and black on the same phase) then the load on the neutral is doubled. I can't think of a load center where if you handle tie the single pole breakers or install a double you will feed off the same phase, therefore the code revision requiring handle ties on MWBC resolves this problem. I recommend in all my inspections that homeowners bring their older MWBC breakers into compliance by installing handle ties.
 
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