Sorting Out Shared Neutral

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  #1  
Old 12-31-13, 09:19 AM
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Sorting Out Shared Neutral

More MWBC questions. Im trying to figure out where the neutral splits in a mwbc I have without taking it all apart and testing with a multimeter.

Outlet box between a ceiling box and the panel I have 2 hots (black) to circuit A bundled together with pigtail to an outlet. 1 hot (red) to circuit B passing thru the box unspliced. And there are 2 neutrals bundled together with a pigtail to that outlet in the that box. (since there are only 2 not 3 neutrals here with the pigtail I think this is between the split and the panel)

In the ceiling box there is a fan/light combo. There are bundled hots circuit A (black) pigtailed with one yellow (switch leg) that gives power to fan/light. There is also 1 hot (red) CIRCUIT b passing thru the box unspliced.

There are 4 neutrals bundled together with the fixture wire. (5 total under 1 red wire nut).

The light switch that controls that fixture only has 1 black and 1 yellow.

I am confused here if the ceiling box contains the split of the neutrals since I have 2 other outlets in the room, both have only power in and power out (2wires in each box) to them, they are fed I believe from the ceiling box.

Does it seem the split of the neutrals is in the outlet box, ceiling box or neither.....


(Let me know if that makes no sense whatsoever and I thank you very much for the bandwith I have taken here to ask my questions)
 
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  #2  
Old 12-31-13, 09:41 AM
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The neutral may not split at all. You have two boxes where a red passes through unspliced. This red may, or may not be be a multi-wire circuit.A good indication of a multi-wire circuit is where you have two hots (black/red, but not always) with a single neutral in a conduit or cable. But this is not always the case, the other colored wire could just be a switch leg. To confirm this you could use a meter and take a reading between hots. You should get 240V.

One thing I am wondering is why is this a concern? IMO you should check to make sure the splices are solid, and when you are working on the circuits turn them off. That way you will not get a shock from the hots or neutrals.
 
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Old 12-31-13, 10:07 AM
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It is a MWBC, the red passing thru is on a different circuit. Also disconnecting the neutrals at the outlet box with power off to only one circuit opened the other circuit as well (almost learned the hardway).

So with the info provided, is it possible to assume where the split is?

One thing I am wondering is why is this a concern? IMO you should check to make sure the splices are solid, and when you are working on the circuits turn them off. That way you will not get a shock from the hots or neutrals.
That's my reasoning for finding out, want to know where the splice is. And of course, Im not working hot.....
 
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Old 12-31-13, 02:51 PM
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If I have to find the common point in a MWBC ..... I'll turn off one circuit and write down what it controls. Then I'll turn it back on and do the the same for the other circuit.

The common point is usually, but not always, where the two circuits are the closest. It's not an exact science as each person has their own idea of how to run a circuit. You are looking for a three wire cable in the box. You'd then check for 240v between the red and black.

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  #5  
Old 12-31-13, 04:42 PM
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Hi PJ thats what I was trying to do. Both boxes in question have hots (black and red) from 2 different circuits. However, one of them just passes thru unspliced.

this might be over my head....
 
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Old 12-31-13, 05:08 PM
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Well.... it can't travel thru unspliced unless you are working with conduit.

You never mentioned it..... are you working in conduit there ?
 
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Old 12-31-13, 05:15 PM
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Yes, all this is in emt.

happy new year.
 
  #8  
Old 12-31-13, 06:14 PM
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You have red, black, and white entering the outlet box you mentioned first, and red, black, and white continuing on from that box. So it looks as if the neutral does not split there --- but --- you have a receptacle in that box fed by the black and of course also by the white. That is a neutral split!

Up in the ceiling box, you have black and white going off elsewhere without the red. And you have red and white going off elsewhere without the black. Those are neutral splits.

In a correctly wired circuit, the neutral accompanies the hot everywhere.

In years past, switch loops did not need neutrals accompanying the hot wires and these are grandfathered.
 

Last edited by AllanJ; 12-31-13 at 06:39 PM.
  #9  
Old 01-01-14, 08:09 AM
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Kind of thinking out loud here.

In the first outlet box there are 3 neutrals and one of those is the pigtail to the outlet. So that could not be the split since there would have to be a 4th wire to be the split. This is likely an outlet between the split and the panel (and I pigtailed the connection here per NEC, it used to be fed thru outlet).

In the ceiling box, there are 4 neutrals + fixture wire neutral = 5 wires under red wire nut.

If the split was in the ceiling, there would have to be L1 and L2 and the neutral back to the panel. That's 3 wires.

There are two other outlets in the room. Both have only 2 wires going to them so that means they are fed from ceiling boxes too. One of those are likely the other neutral in the box leaving the other outlet being fed from elsewhere.....

So the split isn't in the first outlet box, its likely in the ceiling or neither... anyone want to come over and check this out? This isn't going to work on the forum I don't think....
 
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Old 01-01-14, 01:30 PM
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anyone want to come over and check this out? This isn't going to work on the forum I don't think....
I would if the commute wasn't so far.

From what it sounds, none of the boxes you have listed sounds like where it splits. Likely you will have a box where one conduit there is a black, red, and white that enters. And one or two conduits where a red and white leave or just a black and white leave.

The other thing is it might not just separate in one spot. I have wired multi-wires where one box uses the red circuit, next the black, next the red, next the black, etc. All sharing the same neutral.
 
  #11  
Old 01-01-14, 02:41 PM
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Thanks Tolyn, im coming to that conclusion too... its more complex maybe than I hoped.


I looked at the ceiling box again today. It has 4 pipes connected to it. One contains the black (L1), red(L2) and neutral from the outlet box below. Two other pipes only have a black and white (I am assuming these are the two going down to the other two outlets in the room).

The 4th has the red (which passes thru box unspliced) a black, a white and the yellow switch leg. However, in the switch box there is only a black and yellow. There are two ceiling boxes in the closet for overhead lights I think now is between the switch box and the ceiling box. Since the switch box doesn't have a red, I think the split is in one of those. The switch leg must pass through one of those before going into the ceiling box in the room.

The room next to these ceiling boxes is where the other circuit (red wire) is used.

Its enough to give someone aneurysm! If anyone is out there reading trying to make sense of this I thank you.... because I know I am not making much sense probably.
 
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Old 01-01-14, 02:49 PM
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The 4th has the red (which passes thru box unspliced) a black, a white and the yellow switch leg. However, in the switch box there is only a black and yellow. There are two ceiling boxes in the closet for overhead lights I think now is between the switch box and the ceiling box. Since the switch box doesn't have a red, I think the split is in one of those. The switch leg must pass through one of those before going into the ceiling box in the room.
I think you are on the right track with the above, and the fact the next room used only the red.
 
  #13  
Old 01-01-14, 02:54 PM
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I think you are on the right track with the above, and the fact the next room used only the red.
If that is the case, the neutral connection will likely be a taped and soldered connection rather than a wirenut. Is that something I should be concerned about? Meaning the the critical neutral has an old school connection like that?

Either I find it and cut it and put on a nut or just don't touch it at all since its been in service so long.
 
  #14  
Old 01-01-14, 03:30 PM
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A splice can not rely on solder alone. If you have a splice like that, remove the tape and install a wirenut. No need to cut it apart or remove the solder, just install the wirenut over it and forget the tape.
 
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