Conduit used as neutral?

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  #1  
Old 04-02-01, 08:15 AM
HomeownerJ
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Awhile back I posted a question regarding two branch circuits sharing a neutral in the same conduit. This question applies to that same circuit but is independent of that issue.

I was working in a junction box that contains circuit #13, #14 and a shared neutral. The wires come in from the service box and exit in several directions. All three wire connections were soldered and taped, so I removed the tape, cut the soldered blob and stripped the wires for wire nuts. Since I was going to be working on #13 only, I put a wire nut on all the #14 hots. #13 hot and neutral were still disconnected.

I needed to test something so I turned #14 breaker on. I tried a light switch thinking that the light would not work and was surprised that it did. I rechecked the wires and confirmed that only one wire (hot) was connected.

I shut the breaker off again and found the reason that the circuit works with only hot: there is a dead short between neutral and the conduit. I would expect to find a short if I was looking back toward the service entrance since they are connected there. But I had separated the neutrals and was checking the "downstream" portion of the circuit.

So I decided to check out the service entrance. We have two four-inch boxes that are stacked together. Four branch circuits come into these boxes and then there are two short conduit runs bringing these circuits into the panel.

One of the circuits comes into the four-inch box via flexible cable. The hot wire is connected to the hot wire that goes into the panel. The neutral wire is cut and capped with a wire nut. No other wire is connected to this!

It appears that the conduit is being used for neutral. In the first case, it may be unintentional since there is a separate neutral wire. But in the second case, it appears as though the flexible cable was purposely used as the neutral.

Now, I know this is wrong and I know this is bad, my question is "How bad?"

What are the ramifications of using conduit as neutral?
Should I stop using these circuits immediately or is it OK to use them until I can correct the problem?

Thanks.
 
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  #2  
Old 04-02-01, 12:16 PM
solipsist9
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kill this circuit immediately until it's fixed. NEVER use any kind of raceway or ground wire for a neutral. this is extremely dangerous, especially to individuals using the circuit. contrary to what many believe, the neutral carries current as part of its normal routine and one can get electrocuted from the neutral. the ground should never carry current in a normal situtation.

are you sure you've identified the right neutral? is it possible that another neutral is tied to this circuit somewhere? if it's as you say it is, run neutral wires and don't use that ground path as a neutral path.
 
  #3  
Old 04-02-01, 05:57 PM
Wgoodrich
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solipsist9 is right, you have a rather dangerous condition and the circuits should be de energized until you have localized the problem.

solipsist9 also touched on what I suspect is your problem which is also dangerous when you have a shared neutral.

I suspect that you have another white wire connected into those circuits from another set of circuits. Many times electricians unknowingly tie all whites together in a j=box not knowing that you are connecting more than one grounded leg or neutral to those circuits. If this is done you have a mismatch that can cause a white grounded leg to become overloaded carrying the return path of more than one circuit on the same phase back to the panel.

To confirm what solipsist9 suggested, I would shut off the main breaker to ensure no power to the whole house. Then I would isolate the conduits from the box containing the two hot wires in common with that neutral. If the conduit is truly carrying the neutral load the light will no longer work.

If what I suspect that another white wire has been unknowingly connected to those two hots that are supposed to be using the shared neutral, the light will work even with the metal conduits isolated causing a break in the return path to the panel where the conduits are thought to be used as a neutral.

Get back to us and let us know what you find

Wg
 
  #4  
Old 04-04-01, 08:43 AM
HomeownerJ
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I agree that it is a problem and am going to correct it.

But I would like to understand exactly what the problem is.
What fault conditions are required to make this unsafe?

In the case of the circuit that does not have a neutral and is using flexible cable for this, it would seem that the fault condition would be a break in the cable. Someone touching the cable (or any box or conduit attached to it) after the break would form the return path.

For the circuit that has a neutral which is shorted to the conduit, it would seem that both the conduit and the neutral would have to fail to be unsafe. Is this correct?
 
  #5  
Old 04-04-01, 12:27 PM
Wgoodrich
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If a conduit is carrying a neutral load then that conduit is now a current carrying conductor introducing an electrical current onto all pieces of metal in you home. To touch you washer's metal frame may be a shocking experience you may not live through to remember.

If a grounded leg which is white wire that acts as the return path thus completing the cirucit of a 120 volt circuit can only carry the maximum amps of that one 120 volt circuit. If you inadvertantly connect two 120 volt circuits of the same phase to one white wire then you can induce a load on the grounded leg twice as much as the capacity of that white wire, then you have a fire hazard.

I suspect that if you research your problem you should find that the conduit is not acting as the neutral but that you have two white wires connected to the same three or more circuits trying to carry the load of all. If this is true then you have a fire hazard.

To confirm if that conduit is carrying a current of the unbalanced load of your two hot wires of two hot phases then just disconnect the power then break the conduit creating the path back to the panel. Then turn on those two breakers and see if they still work. If the two circuits work properly then the conduit is NOT energized carrying the unbalanced load of those two circuit. Then if the circuits are working properly with the conduit separated then we know that the conduit is not acting as your neutral. Now turn one circuit on at a time only, testing each circuit with the other circuit off. If one or both of the circuits stop working then you have one phase acting as a neutral of the other phase. If one or both of the circuits continue to work individually and the conduit is separated breaking its path to the panel then you have an extra white wire designed to serve a third circuit acting as the return path of all three circuits. This would mean you have an overloaded white wire.

You have a hazard, you should research and find the problem as discribed above. If you don't then you are asking for a shock hazard to people or a fire hazard to the building. Niether picture is pretty if an accident happens in this scenerio.

Hope this helps

Wg
 
  #6  
Old 02-22-14, 12:14 AM
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I know this is an old post, but i've just found that i have this exact problem

Hello,

I have this same problem, I can literally power a pigtailed light bulb from any hot wire to the conduit, or junction box in the system. The conduit reads 125V on the voltmeter from every wire (14 ga) to the conduit.

I'm in Canada. The townhouse is from the late 60's. Ungrounded 2 wire (thhn) throughout the unit with mostly 1/2"emt, some larger emt from the panel to the first junction box and to the 220V outlets.

There are some very, very busy (probably too busy) junction boxes with 12 or more wires nutted together. 90% of the lights and outlets on 2 15A circuits.

The previous owner has made some additions with BX and romex, one gfci breaker that used to be for a jetted tub, but I've deleted it.

What's the first step in isolating and locating the short?

Thanks for any help!
 
  #7  
Old 02-22-14, 12:24 AM
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If your conduit is grounded you will be able to measure voltage from the hot even without a short. Why do you think there is a short?
 
  #8  
Old 02-22-14, 12:30 AM
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There are no ground conductors in the conduit or panel, I expect from other posts here that the conduit itself is intended to act as the ground. But I'm not getting .05V from hot to conduit, if I wire nut the black into any hot wire in any junction box, and touch the white of the pigtail light to the junction box or conduit, it lights all the way up. The box and conduit is entirely live and carrying current.

I thought I had read in Wg's post that it was a short to be found, but upon re-reading, perhaps it isn't short. It's still a major problem that I would like to address.
 
  #9  
Old 02-22-14, 01:05 AM
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After finding and reading:

http://www.homeinspector.org/resourc...h-Circuits.pdf

"...can overheat the neutral wire, even to the point of causing it's insulation to fail, without tripping the breakers (this is because the load on each individual breaker does not exceed it's rating)."

This seems like what's happened in my conduit. I think the previous owner, who made some changes and additions, changed breaker positions to make room for a gfci, but didn't take into account the bus position of the mwbc.

It seems likely then, that the neutral "somewhere" in the conduit has overheated, the insulation has failed, and the breaker has not tripped. That's a short no?
 
  #10  
Old 02-22-14, 03:33 AM
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The conduit itself is the equipment ground. Neutral and equipment ground is bonded at the service panel meaning that the electrical potential is the same for both the neutral and the equipment ground.

While it is possible that you have damaged insulation on a neutral wire allowing contact of the conductor to the conduit the likelihood of this being true is quite low. In a properly bonded system it is normal to measure the line-to-neutral voltage between line and equipment ground or metallic conduit. You could isolate all the neutral wiring and test for continuity between neutral and the conduit but I think doing so would be a waste of time. There are only a few places, entering or leaving enclosures, where a neutral conductor-to-conduit insulation failure might take place and if you REALLY think such a failure HAS taken place it would make more sense to look at these places than to disconnect everything and test the individual conductors.

Checking for a mis-wired MWBC would be fairly easy in comparison.
 
  #11  
Old 02-22-14, 08:40 AM
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It sounds like circuit 13 and 14 are using single pole breakers. If they do in fact share a neutral, you should change this to a two pole breaker, to prevent a load on the neutral when only one circuit is shut off.
 
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