Can I combine multiple neutral wires into a single wire.

[steve66]

Seems like I should know the answer to this, but I'm really not sure. Maybe its just because its getting late & I'm not thinking straight.

Say for example I have six branch circuits running in a single conduit. Say they are all 20 A branch circuits serving receptacles throughout a large area. Also assume its a 3 phase system, and the circuits are 1,3,5 and 7,9, and 11. So I have two multiwire branch circuits each with its own #12 neutral wire.

Could I combine the two neutral wires into a single larger neutral? I'm assuming the new neutral wire would need to be rated for 40 amps, so maybe it would be a #8.

To take this farther, if I had (4) multiwire branch circuits, could I use a single 80A neutral wire?? For example, assume I had the first 12 circuits on a panel running in the same conduit.

I just started thinking about this because I have a conduit run with several neutral wires. The conduit and branch circuits stop at several different outlets. It suddenly seems odd to have several neutral wires in the same conduit. I'm not sure how the electirican is going to keep track of which neutral wire goes with witch multiwire circuit. If he gets a neutral crossed in a jbox, then suddenly the same neutral might be serving circuits 1 and 7, and it could possibly be overloads.

Steve

 

[texie]

Sorry, not anymore. See NEC 2011 200.4

 

[steve66]

Sorry, not anymore. See NEC 2011 200.4

Wow, this was actually allowed under the 2008? That's suprising.

Anyhow, no need to be sorry. It actually saves me from redrawing a bunch of circuits.

For anyone interested, the exceptions appear to be in 215 for feeders, and 225 for outdoor lighting circuits.

 

[hurk27]

Actually since the neutrals run to the same neutral bar it is only after you get to the point of where the circuits split up that you have to pay attention to which neutral is paired with which hots, which would remove any reason running a single over sized neutral, since after this point you would need separate neutrals anyways, If I have gray on hand I will use gray for one MWBC and white for the other, but with the new requirements of 2011 and even the changes to the 2008 kind of makes this a mute point, and GFCI breakers and AFCI's would also not like it unless you were using the new GE AFCI's and I don't know of or haven't seen a 3-pole GFCI breaker?

The only time I used this was when I relocated a service panel, and made the old box a junction box leaving the old neutral bar in place, and I just ran all the hots to the new panel, and one neutral sized to the old panel neutral bar to pick up the existing neutrals, saved some wire, but that was some years ago, and I remember discussing it here, and remember some didn't like it, but back then there wasn't any code that prevented it. many all in one manual transfer panels with the load center also did this from the factory. the other place I saw this as factory wiring was office cubicle wall assembles where they would have 4 or 5 circuits with one or two over sized neutrals in the feed flex. but the 2011 ended it.

 

[jumper]

It was Don G's proposal that got this section added.

 

[Dennis Alwon]

Even in 2008 I don't see how you would be able to comply with 210.4(B) -- simultaneously opening all ungrounded conductors.

 

[infinity]

Even in 2008 I don't see how you would be able to comply with 210.4(B) -- simultaneously opening all ungrounded conductors.

I agree, and that kind of takes the wind out of the sails of the permission in Article 225 making that somewhat moot.

 

[kwired]

As far as multiple neutral conductors in the same raceway you are limited to white, gray, and white or gray with stripes or other markings. Nothing says you can't field mark them somehow to indicate which one is which.

I would even use phase tape to mark them same as phase conductor they are associated with. Some will criticize me for this because how are you supposed to tell them apart from white conductors that have been reidentified as an ungrounded conductor? I think that whole idea is stupid to begin with (try convincing me that a white conductor landed on a breaker terminal is a neutral). Besides if the conductors are in a raceway you can not reidentify white conductors as ungrounded conductors anyway. You can also use number markers or something like that.

 

[steve66]

Even in 2008 I don't see how you would be able to comply with 210.4(B) -- simultaneously opening all ungrounded conductors.

I thought there might be a way to tie 6 handles together (ie. 1,3,5,7,9, and 11). But that would eliminate any possiblilty of using the evens and the odds on the same neutral.

This is actually all outdoor. Its streetlights with a heavy mix of receptacles, which keeps the exception from applying.

Since its outdoors, I'm more concerned with the electrician getting the neutrals crossed than overloading one. If the wrong neutral is spliced and ran to a outlet, it could still be hot even when the breaker serving the outlet is turned off.