Pigtailed neutrals on MWBC

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wwhitney said:
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
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If you remove the device and nothing bad happens downstream then the wiring is code compliant.
 
In that MH graphic we are at the end of the three portion of the MWBC, but we can not pass the neutral through the receptacle and then on to the final two 2 wire portions of the circuit, removing the receptacle would open a portion of the common neutral.
 
jumper said:
This what you want?

30013b001web2.gif
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Okay, I see the issue now. That receptacle on the left is the last of the line on the MWBC. It then goes to 2 2 wire circuits. That last receptacle on the MWBC does NOT need a pigtail. Any receptacles before it would.

If you cut the neutral at the left receptacle, there is no way you'd have the possibility of loads on the receptacles downstream seeing (up to) 208 or 240V. I'm going back to what I coin "Dave's Rule" re: MWBC:

"If you remove the device and nothing bad happens downstream then the wiring is code compliant.""

eta: if you lift/cut/break the neutral at the left-most device, you simply have 2 open 2 wire circuits downstream
 
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JFletcher said:
Okay, I see the issue now. That receptacle on the left is the last of the line on the MWBC. It then goes to 2 2 wire circuits. That last receptacle on the MWBC does NOT need a pigtail. Any receptacles before it would.

If you cut the neutral at the left receptacle, there is no way you'd have the possibility of loads on the receptacles downstream seeing 208 or 240V.
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That left receptacle, if not pigtailed, would have 3 white wires going to it: one supply neutral and two neutrals for the two downstream 2-wire circuits. Say it is a back clamp type receptacle so that each screw can take 2 wires. If the supply neutral is going to one screw, and the other two neutrals are going to the other screw, and you open the supply neutral first, then the loads on the two downstream 2-wire circuits will be in series and supplied with 240V.

Cheers, Wayne
 
wwhitney said:
That left receptacle, if not pigtailed, would have 3 white wires going to it: one supply neutral and two neutrals for the two downstream 2-wire circuits. Say it is a back clamp type receptacle so that each screw can take 2 wires. If the supply neutral is going to one screw, and the other two neutrals are going to the other screw, and you open the supply neutral first, then the loads on the two downstream 2-wire circuits will be in series and supplied with 240V.

Cheers, Wayne
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I was just about to edit my post to change my stance to reflect what you just wrote. You and Mike are correct, I am in error, tho I still stand by "Dave's Rule".
 
Let's do this.

Go to this house and flip the GD switch on and let it run.
We'll also turn on the dishwasher and let it run also.

Then we'll get under the sink and pull the receptacle out of the box hot with the GD and dishwasher left plugged in and running with no wires removed from the receptacle.

Once we get the receptacle out of the box we'll take the neutral off of the neutral side of the receptacle that's headed to switch but leave the neutral coming from the panel terminated on the receptacle so our GD and dishwasher will remain running.

Now, what happened?

Nothing happened.

The GD and dishwasher are running fine and we haven't burned anything up.
Why? Because the circuit headed up to the switch and beyond if it does,,is not a MWBC.

If the red circuit does happen to extend beyond the GD switch,whatever is on that circuit will go out because of the lifted neutral ,but ,it will cause no harm.

That neutral from the receptacle up to the switch need not be under the pigtail since removing the receptacle will not affect that part of the circuit like it would if you separated the neutral connection anywhere ahead of that point.

But like I said earlier, I always pigtail anyway.


Jap>
 
jap said:
Let's do this.

Go to this house and flip the GD switch on and let it run.
We'll also turn on the dishwasher and let it run also.

Then we'll get under the sink and pull the receptacle out of the box hot with the GD and dishwasher left plugged in and running with no wires removed from the receptacle.

Once we get the receptacle out of the box we'll take the neutral off of the neutral side of the receptacle that's headed to switch but leave the neutral coming from the panel terminated on the receptacle so our GD and dishwasher will remain running.

Now, what happened?

Nothing happened.

The GD and dishwasher are running fine and we haven't burned anything up.
Why? Because the circuit headed up to the switch and beyond if it does,,is not a MWBC.

If the red circuit does happen to extend beyond the GD switch,whatever is on that circuit will go out because of the lifted neutral ,but ,it will cause no harm.

That neutral from the receptacle up to the switch need not be under the pigtail since removing the receptacle will not affect that part of the circuit like it would if you separated the neutral connection anywhere ahead of that point.

But like I said earlier, I always pigtail anyway.


Jap>
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Apply filter =>>>>> Dave's Rule for MWBC and you end up with a one line post.
 
JFletcher said:
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.
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ActionDave said:
I agree.



You don't have to pigtail.
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X3

ActionDave said:
If you remove the device and nothing bad happens downstream then the wiring is code compliant.
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And this may sound harsh, but imo, if one were to insist one pigtailing all of the devices in a mwbc b/c of an obscure interpretation of 300.13, he's wasting time and in esp new resi that means hes wasting money, and would be let go....



wwhitney said:
That would be a nice way to write 300.13(B), perhaps you should submit a public input. :)

Cheers, Wayne
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I'd vote to leave it alone as written----nothing incorrect about how its written.;)

Its not an issue, and if somebody doesn't quickly understand why its unnecessary to pigtail end of the run devices on part of an MWBC,
then they had no business anywhere near the installation to begin with.

But getting back to the word smithing.....Look hard at the wording of 300.13(B), think about what a MWBC is, and what is technically past the split point on a MWBC.....you'll quickly get your answer as to why there's nothing wrong with how its written.:)
 
jap said:
Let's do this.

Go to this house and flip the GD switch on and let it run.
We'll also turn on the dishwasher and let it run also.

Then we'll get under the sink and pull the receptacle out of the box hot with the GD and dishwasher left plugged in and running with no wires removed from the receptacle.

Once we get the receptacle out of the box we'll take the neutral off of the neutral side of the receptacle that's headed to switch but leave the neutral coming from the panel terminated on the receptacle so our GD and dishwasher will remain running.

Now, what happened?

Nothing happened.
Click to expand...
Do the same experiment, but remove the incoming white wire from the receptacle instead of the outgoing white wire.

Now what happened?
 
jumper said:
I get to watch!!!
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I'd like to watch too if that's the one you want to pull off but this post is not about that one.
It's about the one connected to that one going to the GD switch.

Jap>
 
jap said:
That's what the rule is for.
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:
That's why I believe the pigtail is required in this example: technically speaking, the multi-wire circuit extends "through" the box (like when you say 'one through ten'), even though it also ends in the box.

Opening the neutral with both appliances operating places them in series across 240, and creates a shock hazard with either in use. I realize that that's why multi-wire circuits require tied breakers.
 
jap said:
I'd like to watch too if that's the one you want to pull off but this post is not about that one.
It's about the one connected to that one going to the GD switch.
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To me, it's about both. They're not separate entities.

You wouldn't pigtail a single conductor.
 
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