MWBC

[Little Bill]

If you were running several 20A MWBC(s) using 12-3, and you ran out of 12-3, and completed the install using (2) 12-2, would you tie both neutrals together or cap one off?
Seems if you tie them together you would be creating a parallel circuit and the #12 is too small for that.

FYI: There is a reason to keep the MWBC and not change to individual circuits.

 

[Dennis Alwon]

I guess to avoid the parallel neutral you could cap one off and run the cables together so there isn't any electromagnetic field. I believe 300.3(B)(3) allows this if you comply with 300.20(B)

 

[jaggedben]

I don't get it.

If it's required to keep them an MWBC (say, if it serves a single appliance) then using two 12/2 was a code violation, so I wouldn't have done that.

Otherwise, I can't think of a reason to keep them an MWBC.

 

[Little Bill]

I don't get it.

If it's required to keep them an MWBC (say, if it serves a single appliance) then using two 12/2 was a code violation, so I wouldn't have done that.

Otherwise, I can't think of a reason to keep them an MWBC.

There are double outlets dropped from the ceiling and are on a MWBC and are also switched. 12-3 is already ran to the drop junction box and the 12-4 cord is already installed along with the double quads on the end of the cords. 12-3 is already run to the switches. The problem is I ran out of 12-3 to feed the line side to the switches. There's already a single neutral at all locations other than panel to switches. I would have to run a cable with another neutral to change them to single circuits.

 

[wwhitney]

If it's required to keep them an MWBC (say, if it serves a single appliance) then using two 12/2 was a code violation, so I wouldn't have done that.

It's not actually a code violation. Dennis provided the code citations and the concerns.

As to the OP, if you don't want to cap the spare white at each end, you could reidentify the spare white as a green and tie it in with the two bare conductors. Since the EGC is not subject to the limit on parallel conductors. EGCs are often parallel.

Cheers, Wayne

 

[Rick 0920]

It's not actually a code violation. Dennis provided the code citations and the concerns.

As to the OP, if you don't want to cap the spare white at each end, you could reidentify the spare white as a green and tie it in with the two bare conductors. Since the EGC is not subject to the limit on parallel conductors. EGCs are often parallel.

Cheers, Wayne

I was not aware that you could reidentify a white or gray insulated conductor as anything other than an ungrounded conductor. Would you please provide that reference? Thanks.

 

[Earthed]

I say not allowed. 300.3(B) Conductors of the Same Circuit.

 

[wwhitney]

I say not allowed. 300.2(B) Conductors of the Same Circuit.

Presumably you mean 300.3(B). As Dennis pointed out, 300.3(B)(3) does not require all the conductors to be in the same cable when the cable has a "nonmetallic or nonmagnetic sheath." That certainly covers NM.

Cheers, Wayne

 

[wwhitney]

I was not aware that you could reidentify a white or gray insulated conductor as anything other than an ungrounded conductor. Would you please provide that reference? Thanks.

250.119(C) permits reidentifying a conductor of a multiconductor cable to be green to be used as an EGC. It has no requirements on the color of the underlying insulation. Is there some other section that would restrict reidentifying a white conductor?

Cheers, Wayne

P.S. That's the 2023 reference; in the 2020 NEC it's 250.119(B). And in the 2017 NEC, that section is restricted to "Where the conditions of
maintenance and supervision ensure that only qualified persons service the installation." But that restriction was removed in the 2020 NEC.

 

[Dennis Alwon]

Years ago when I was in NT we did some subcontract work for IBM. They required a ground for the BX cable so we ran 12/3 and stripped the red wire and used it as an equipment grounding conductor.

 

[Dennis Alwon]

I wrote a proposal years okay to get 300.3(B) changed so that NM cable would not be allowed to be run in different cables which often creates electromagnetic field's. They did not seem concerned about electromagnetic field's so it did not get accepted.

 

[wwhitney]

I wrote a proposal years okay to get 300.3(B) changed so that NM cable would not be allowed to be run in different cables which often creates electromagnetic field's. They did not seem concerned about electromagnetic field's so it did not get accepted.

That concern is not unique to NM cable, so you'd have to get rid of 300.3(B)(3) entirely to achieve that. But as long as you run the multiple NM cables together as a bundle, I believe the issue is minimal.

Cheers, Wayne

 

[Earthed]

Presumably you mean 300.3(B).

Yes

I don't see how you can 'group' all the conductors. You have 2 separate raceways.

 

[Dennis Alwon]

That concern is not unique to NM cable, so you'd have to get rid of 300.3(B)(3) entirely to achieve that. But as long as you run the multiple NM cables together as a bundle, I believe the issue is minimal.

Cheers, Wayne

My proposal was to get rid of 300.3(B)

 

[Dennis Alwon]

Yes

I don't see how you can 'group' all the conductors. You have 2 separate raceways.

Let's be clear 300.3(B) does not require the non-ferrous cable or raceways to be grouped. Grouping helps alleviate the electromagnetic field's but as I said earlier, the NEC is not concerned about that.

I also want it to go on record that I would not do this even though it is allowed.

 

[Rick 0920]

250.119(C) permits reidentifying a conductor of a multiconductor cable to be green to be used as an EGC. It has no requirements on the color of the underlying insulation. Is there some other section that would restrict reidentifying a white conductor?

Cheers, Wayne

P.S. That's the 2023 reference; in the 2020 NEC it's 250.119(B). And in the 2017 NEC, that section is restricted to "Where the conditions of
maintenance and supervision ensure that only qualified persons service the installation." But that restriction was removed in the 2020 NEC.

The other reference is 200.7 (C) circuits of 50 volts or more. It uses the wording "ungrounded conductor" making me think that reidentification would pertain to only that. Thank you.

 

[wwhitney]

The other reference is 200.7 (C) circuits of 50 volts or more. It uses the wording "ungrounded conductor" making me think that reidentification would pertain to only that.

Good catch, 200.7 prohibits my idea of reidentifying the white conductor using green tape.

250.119(C) also offers the option of stripping all the exposed insulation to yield a bare conductor. It's unclear to me whether that would still violate 200.7 for the white conductor. I.e. if you strip the exposed insulation, does it till have a "continuous white" covering, or is it no longer continuous?

But that would be a more permanent change, so capping both ends seems better. You could further reidentify it with some colored tape to make it even clearer it's not meant to be the grounded conductor.

Cheers, Wayne

 

[Rick 0920]

Good catch, 200.7 prohibits my idea of reidentifying the white conductor using green tape.

250.119(C) also offers the option of stripping all the exposed insulation to yield a bare conductor. It's unclear to me whether that would still violate 200.7 for the white conductor. I.e. if you strip the exposed insulation, does it till have a "continuous white" covering, or is it no longer continuous?

But that would be a more permanent change, so capping both ends seems better. You could further reidentify it with some colored tape to make it even clearer it's not meant to be the grounded conductor.

Cheers, Wayne

I think we've all been there before. The end of a big job and we find that we have a lot of 1 color left. We don't want to order 1000' feet of colors when we have 5000' feet of yellow left! I realize IT ISN'T code compliant to do it, but I think we all have at one time or another. Is it really unsafe? Maybe to untrained persons that happen to get into a box and assume that a wire of a certain color is in fact a ground, neutral or hot. A #12 brown has the same amount of copper as a #12 white. Shhhhhh! If you don't tell that wire what color it is, it will never know!

 

[letgomywago]

I think we've all been there before. The end of a big job and we find that we have a lot of 1 color left. We don't want to order 1000' feet of colors when we have 5000' feet of yellow left! I realize IT ISN'T code compliant to do it, but I think we all have at one time or another. Is it really unsafe? Maybe to untrained persons that happen to get into a box and assume that a wire of a certain color is in fact a ground, neutral or hot. A #12 brown has the same amount of copper as a #12 white. Shhhhhh! If you don't tell that wire what color it is, it will never know!

I don't like doing that but if you have something that doesn't quite match like for switching and so not a technical violation just something that doesn't match I don't mind doing that.

 

[don_resqcapt19]

Yes

I don't see how you can 'group' all the conductors. You have 2 separate raceways.

It is because 300.3(B)(3) acts as an exception to the parent text in 300.3(B).

(B) Conductors of the Same Circuit.
All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, conduit body, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).
...
(3) Nonferrous Wiring Methods.
Conductors in wiring methods with a nonmetallic or other nonmagnetic sheath, where run in different raceways, auxiliary gutters, cable trays, trenches, cables, or cords, shall comply with 300.20(B). Conductors in single-conductor Type MI cable with a nonmagnetic sheath shall comply with 332.31. Conductors of single-conductor Type MC cable with a nonmagnetic sheath shall comply with 330.31, 330.116, and 300.20(B).

The only requirement for for a non-metallic wiring method is that the ends of multiple cables or raceways used for a single circuit comply with 300.20.