Pigtailed neutrals on MWBC

[al hildenbrand]

So reading 300.13(B) a little more closely, I see that the wording is ambiguous. You could read it as referring to ((continuity within the MWBC) of the grounded conductor) or as (continuity of the grounded conductor) within the MWBC). In the former reading, the receptacle doesn't need pigtailing, as it is at the end of the MWBC, at least for the usual reading of the definition of MWBC, so if you interrupt the grounded conductor there, the grounded conductor is still continuous within the MWBC. Under the latter reading, which I hadn't previously considered, the device needs pigtailing.

300.13(B) speaks about the continuity of the grounded conductor being interrupted by the removal of a device. . . If the grounded conductor OF THE MWBC lands only on the duplex receptacle terminals, removal of the duplex receptacle WILL interrupt the continuity "of the grounded conductor."

 

[al hildenbrand]

So reading 300.13(B) a little more closely, I see that the wording is ambiguous. You could read it as referring to ((continuity within the MWBC) of the grounded conductor) or as (continuity of the grounded conductor) within the MWBC).

This is not and either / or. And it is not ambiguous. Both meanings are correct.

 

[LarryFine]

Interesting discussion. My take is that the pigtail is required, because it's perfectly foreseeable that a circuit extension could be added at the switch without awareness of the lack of a pigtail.

I'm not saying that we have to wire to suit the what-if-in-the-future... scenario, but that the neutral leaves the box with the split receptacle as if it IS used downstream. Otherwise, cap it off.

One could say that the pigtail would have to be added in the future if someone did add such a circuit addition, but, to me, the pigtail is needed because the neutral, used or not, leaves the box.

Added: And yes, a switch box is an outlet if a switch in a bedroom that controls a load outside the bedroom requires AFCI protection.

 

[kwired]

There lays the problem. We are required to have a neutral at the switch location.

Doesn't matter if it is used or not as far as the NEC is concerned.
​

I have to admit that the installer did this correctly although I sure wouldn't have thought of it for a GD switch. He just didn't pigtail the neutral at the device where the MWBC is utilized for line to neutral loads.

Add: He didn't have handle ties at the CBs either

I was thinking as I was reading through the posts that this might be why a neutral was ran for this, you only need the grounded conductor at the switch if it is controlling lighting outlets 404.2(C).

The fact it is extended from a multiwire circuit still means it would need to be pigtailed if actually in use. reality is it likely don't even need to be there, so unless it is feeding a load just unhook it from the receptacle and call it a spare conductor.

 

[jap]

I was thinking as I was reading through the posts that this might be why a neutral was ran for this, you only need the grounded conductor at the switch if it is controlling lighting outlets 404.2(C).

The fact it is extended from a multiwire circuit still means it would need to be pigtailed if actually in use. reality is it likely don't even need to be there, so unless it is feeding a load just unhook it from the receptacle and call it a spare conductor.

If that's the way it is then the graphic is wrong.

Jap>

 

[jap]

And you just as well say if any circuit is part of a MWBC the grounded conductor must not rely on the device for continuity and all grounded connections must be pigtailed.

I don't see it that way and judging by the graphic there are others that don't see it that way either.

Oh well,, I always pigtail anyway.


Jap>

 

[kwired]

If that's the way it is then the graphic is wrong.

Jap>

I take back what I said - the lines from receptacle to the switch in OP are not multiwire portion of the circuit (120/240 is not present at the switch location).

 

[jap]

I take back what I said - the lines from receptacle to the switch in OP are not multiwire portion of the circuit (120/240 is not present at the switch location).

That's the way I see it also.


Jap>

 

[jap]

Interesting discussion. My take is that the pigtail is required, because it's perfectly foreseeable that a circuit extension could be added at the switch without awareness of the lack of a pigtail.

I'm not saying that we have to wire to suit the what-if-in-the-future... scenario, but that the neutral leaves the box with the split receptacle as if it IS used downstream. Otherwise, cap it off.

One could say that the pigtail would have to be added in the future if someone did add such a circuit addition, but, to me, the pigtail is needed because the neutral, used or not, leaves the box.

Added: And yes, a switch box is an outlet if a switch in a bedroom that controls a load outside the bedroom requires AFCI protection.

The pigtail is only needed if it's associated with a MWBC.
The wiring from the receptacle to the switch in this case is not.

Not even if it leaves the switch and feeds something else.

There is a red and a white with a voltage of 120volts.

There is not 240 at the switch like there is at the receptacle box.

Jap>

 

[wwhitney]

This is not and either / or. And it is not ambiguous. Both meanings are correct.

There really are two way to read 310.13(B):

1) Removing the device must not result in an MWBC with an interrupted neutral. This reading does not require a pigtail, as if you remove the last device on an MWBC, the remaining MWBC still has an uninterrupted neutral.

2) For all points on an MWBC, removing the device must not interrupt the neutral. This reading does require a pigtail, as if you remove the device, you are interrupting a neutral (on a portion of the circuit which is not an MWBC).

Given the reason for the rule, I favor interpretation (1).

Cheers, Wayne

 

[al hildenbrand]

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.

View attachment 19536

1) Removing the device must not result in an MWBC with an interrupted neutral. This reading does not require a pigtail, as if you remove the last device on an MWBC, the remaining MWBC still has an uninterrupted neutral.

Given the reason for the rule, I favor interpretation (1).

There is no additional text in 300.13 that describes the "reason for the rule" therefore there is no additional legally binding text to support your opinion. Mike Holt's graphic above clearly contradicts your interpretation (1), and, also, it is my opinion that a pigtail, or equivalent, is required because the term "grounded conductor" has no way to exclude some grounded conductors present in the box from other grounded conductors that are present in that same box.

 

[wwhitney]

There is no additional text in 300.13 that describes the "reason for the rule" therefore there is no additional legally binding text to support your opinion.

Sure, there's no text, but when a rule has multiple interpretations trying to understand the reason behind the rule is a good way to pick among the interpretations.

Mike Holt's graphic above clearly contradicts your interpretation (1)

Hmm, you raise a very good point. So given the reason as I understand it for the rule, the interpretation I would prefer would be:

(1.5) Removing the device must not result in the possibility of line to neutral loads being fed in series line to line. This would require pigtailing in the Mike Holt diagram, but wouldn't require pigtailing in the OP's case.

However, the text of the 300.13(B) clearly doesn't support that interpretation. So if we must choose between my interpretations (1) and (2), I'm now in the (2) camp.

Cheers, Wayne

 

[wwhitney]

P.S. In a 2-phase system, where the ungrounded phases A, B, C, and D are sequentially 90 degrees apart in phase, a circuit consisting of conductors A, B, C which feeds L-L loads from both A-B and B-C should be subject to a similar prohibition. Breaking the supply connection to conductor B would put the loads in series across A-C, which depending on the load impedances could expose some of the loads to an overvoltage.

But I guess that is too obscure an example to merit a rule in the NEC. In a 3 phase system this problem does not occur, since the B-C voltage is the same as the A-B and B-C voltages.

Cheers, Wayne

 

[kwired]

There is no additional text in 300.13 that describes the "reason for the rule" therefore there is no additional legally binding text to support your opinion. Mike Holt's graphic above clearly contradicts your interpretation (1), and, also, it is my opinion that a pigtail, or equivalent, is required because the term "grounded conductor" has no way to exclude some grounded conductors present in the box from other grounded conductors that are present in that same box.

That picture is not the same thing OP has. OP has MWBC entering the box, but only two wire circuit leaving the box, plus a switched return lead.

 

[wwhitney]

That picture is not the same thing OP has. OP has MWBC entering the box, but only two wire circuit leaving the box, plus a switched return lead.

Right, but I don't think the text of 300.13(B) can reasonably be interpreted to differentiate between the OP's arrangement and the Mike Holt graphic. That is why I changed my mind on the appropriate interpretation of 300.13(B).

Cheers, Wayne

 

[JFletcher]

reading this topic has made my head hurt. I'm not even sure what the debate is: device removal cannot interrupt the neutral on a MWBC. an end of the line receptacle doesnt need pigtailed. there may not be a stated reason for 300.13 but to me it seems pretty obvious: 120V loads are made to run at just that, 120V, not double the load at 240V in series, which is what would happen to a MWBC if you were to lift the neutral, say, at the panel.

 

[wwhitney]

reading this topic has made my head hurt. I'm not even sure what the debate is: device removal cannot interrupt the neutral on a MWBC. an end of the line receptacle doesnt need pigtailed.

Right. But the question is how to treat the last receptacle on the MWBC portion of a circuit, when one (or two, in the Mike Holt graphic) 2-wire circuits extend past the end of the MWBC.

Cheers, Wayne

 

[ActionDave]

reading this topic has made my head hurt. I'm not even sure what the debate is: device removal cannot interrupt the neutral on a MWBC. an end of the line receptacle doesnt need pigtailed. there may not be a stated reason for 300.13 but to me it seems pretty obvious: 120V loads are made to run at just that, 120V, not double the load at 240V in series, which is what would happen to a MWBC if you were to lift the neutral, say, at the panel.

I agree.

Right. But the question is how to treat the last receptacle on the MWBC portion of a circuit, when one (or two, in the Mike Holt graphic) 2-wire circuits extend past the end of the MWBC.

Cheers, Wayne

You don't have to pigtail.

 

[jap]

I agree.



You don't have to pigtail.

I agree but it doesn't seem to be that easy.

Jap>

 

[wwhitney]

You don't have to pigtail.

The Mike Holt graphic shows pigtailing required at the last device on the MWBC when both ungrounded conductors are extended further as part of 2-wire circuits. And the hazard there is real, in that the 120V devices on the 2-wire circuits could be exposed to overvoltage on loss of the neutral. Thus we should interpret 310.13(B) to require that pigtailing.

In the OP's case, where only one ungrounded conductor is extended beyond the last device on the MWBC, the hazard is not present. But the language of 300.13(B) doesn't have anything in it which would distinguish this case from the Mike Holt graphic. So I would say pigtailing is required by the NEC but unnecessary by the physics.

Cheers, Wayne