Two Grounded Conductors in Conduit?

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busman

busman

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Northern Virginia
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Master Electrician / Electrical Engineer
I do mostly residential service work, so I don't do much conduit wiring. Yesterday I came to a JB that had two hots and two grounded conductors. The two hots were on different CB's. There was no marking to differentiate the grounded conductors. In looking at 200-6, conductors of different systems can have stripes on the grounded conductor.

The questions are:

1) Can grounded conductors of the same system be identified in any way, since it appears they are required to have a continuous white covering?

2) If this is permitted, what is the preferred way to do the marking in the field, or is it necessary to buy white wire with a stripe?

It seems that the neutrals of different circuits would need to be kept separate to avoid overloading the neutral, but I am confused about how to implement this.

Thanks (as always),

Mark
 
A lot of the time, there are subtle differences between the two grounded conductors, such as lettering on the insulation by different manufacturers, wire gauge, type of insulation (THHN vs. THW, etc.), or even differences in the batch of plastic hues of "white". But, unfortunately, there are times when there is no difference, or the plastic has aged or been affected by environmental conditions that mask the distinctions that the installer saw.

In your situation, as I understand it from your OP, I'd use something like a ty-rap around one hot and its associated grounded conductor at each end of the raceway that holds two hots and two grounded conductors.
 
Brad,

Thanks for the quick response. I am afraid I am not familiar with the type tags you mentioned. Do you just label them with the color of the hot to which they are related. Yesterdays example had one red and one blue for the hots.

Thanks,

Mark
 
Al,

I really like the ty-wrap idea. That should be obvious to anyone coming behind me. Now I just need to trace these neutrals back to the panel and insure that they are separate the entire way.

Thanks,

Mark
 
Just an FYI Mark, any good circuit tracer can trace the grounded conductor as well as the ungrounded conductor. A lot of guys don't know that they can be used to find the neutral also.

Not to start another debate, but I prefer the Amprobe Phasar.
 
Brad,

Thanks for the help. I have the Amprobe AT-4005 and yes, it can trace anything metallic (ie. conductive). The problem is not tracing the neutral; it is insuring that only loads from ONE circuit are attached to each neutral. If someone before me hadn't labeled the neutrals, then at each outlet, it is possible that the loads are attached to a random neutral. This could cause neutral overloading since there is no OCPD on the neutrals. I don't think a tracer can help me find this.

The only thought I had was that if everything was loaded on both circuits, then I could use a clamp-on to test current and make sure the hot and neutral are the same (sort of a manual GFCI). We all know from experience that crossing neutrals will make it impossible to install a GFCI or AFCI breaker. One of the headaches in older homes for AFCI where joinded neutrals and stolen grounds are common.

Thanks,

Mark
 
benaround said:
Mark,

Do you have a gfci breaker the same make as on the job? Might be quicker to temp it in to check the circuits.

frank
Click to expand...

Great thought!! I was thinking the other day about the advantages of GFCI protecting entire circuits. The " neutral monitoring" is a excellent way to catch wiring problems, ie: crossed neutrals, improper N/G bonds or accidental contacting of N and G. The advantages of protecting a circuit with this type of protection has many safety benefits, and Yes even AFCI's help with this as they have a GFI aspect to them.
 
Back to basics. You mention the hots are on different CBs. Are these CBs on different phases? If so, then there is no problem and no need for two white wires. If not, then you have to keep things sorted out.
In such cases, number book tags are a great help. The white wire might read "2, 4". Is this a 3 phase system? If so, then the neutral can serve three phases.
The use of two hots and two neutrals in one conduit is either unnexessary or the result of bad numbering of circuits in the planning stage or just unavoidable.
Perhaps, you could use gray wire in this situation. I know that gray is usually used to indicate a 277v neutral but, if you make a note of it at the panel, may it should fly.
~Peter
 
Two Grounded Conductors in Conduit?

Every box should have the hot taped to the neutral that goes with it (same as a tye wrap but cheaper). I would shut the power off, unplug all loads, and disconnect both neutrals. Ground one of them, and check every box with a continuity tester and tape the grounded one to the proper hot wire.
 
If so, then the neutral can serve three phases.
Click to expand...

Although it may be, I don't think that we should assume that this is a 3 phase system. .

The use of two hots and two neutrals in one conduit is either unnexessary or the result of bad numbering of circuits in the planning stage or just unavoidable.
Click to expand...

There are many times when circuits are deliberately pulled with separate neutrals. Dimming circuits, or potential harmonic circuits being two examples. Also, we're talking about a junction box. There is no guarantee that these two neutrals aren't shared with other circuits somewhere upstream which would require the two separate neutrals downstream.
 
Re: Two Grounded Conductors in Conduit?

busman said:
I do mostly residential service work, so I don't do much conduit wiring. Yesterday I came to a JB that had two hots and two grounded conductors. The two hots were on different CB's. There was no marking to differentiate the grounded conductors. In looking at 200-6, conductors of different systems can have stripes on the grounded conductor.

The questions are:

1) Can grounded conductors of the same system be identified in any way, since it appears they are required to have a continuous white covering?

2) If this is permitted, what is the preferred way to do the marking in the field, or is it necessary to buy white wire with a stripe?

It seems that the neutrals of different circuits would need to be kept separate to avoid overloading the neutral, but I am confused about how to implement this.

Thanks (as always),

Mark
Click to expand...

While you got that JB open, place a color of tape over the groups so in the future the next guy will know what goes to what if the joints were ever broken.
 
peter said:
Back to basics. You mention the hots are on different CBs. Are these CBs on different phases? If so, then there is no problem and no need for two white wires. If not, then you have to keep things sorted out.
Click to expand...

If this ends up being a desirable option, just be careful not to lose your neutral connection to the panel during the transition from completely separate circuits to a multiwire branch of circuits. Many loads can be damaged if they series with another load of a different impedence on another circuit. Even if you lose the neutral for even just a second, you can fry something.

David
 
Re: Two Grounded Conductors in Conduit?

unimo said:
Every box should have the hot taped to the neutral that goes with it (same as a tye wrap but cheaper). I would shut the power off, unplug all loads, and disconnect both neutrals. Ground one of them, and check every box with a continuity tester and tape the grounded one to the proper hot wire.
Click to expand...

I agree with unimo. Best solution to situation I've seen posted. Just make sure the red and blue do not change color anywhere along the way. I've been fooled by that a couple of times. :)
 
peter-

I know we've all seen what you are talking about many times and perhaps we've wired things this way. But the code has changed on this issue over the years.

Code: 
210.4 Multiwire Branch Circuits
(A) General Branch circuits recognized by this article shall be permitted as multiwire circuits. A multiwire circuit shall be permitted to be considered as multiple circuits. All conductors shall originate from the same panelboard or similar distribution equipment.
FPN: A 3-phase, 4-wire, wye-connected power system used to supply power to nonlinear loads may necessitate that the power system design allow for the possibility of high harmonic neutral currents.

(B) Devices or Equipment Where a multiwire branch circuit supplies more than one device or equipment on the same yoke, a means shall be provided to disconnect simultaneously all ungrounded conductors supplying those devices or equipment at the point where the branch circuit originates. 

(C) Line-to-Neutral Loads Multiwire branch circuits shall supply only line-to-neutral loads.
Exception No. 1: A multiwire branch circuit that supplies only one utilization equipment.
Exception No. 2: Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch-circuit overcurrent device.
FPN: See 300.13(B) for continuity of grounded conductor on multiwire circuits.

On another note, I always thought that 200.6 (D) Grounded Conductors of Different Systems referred to different panelboards, not different circuits on the same panelboard. Comments?
 
On another note, I always thought that 200.6 (D) Grounded Conductors of Different Systems referred to different panelboards, not different circuits on the same panelboard. Comments?
Click to expand...

Yes, you're correct. Different systems are not from the same panelboard.
 
I always thought that "different systems" meant from different power sources, such as from different transformers.

***
One common example:

208/120Y would be one system

480/277Y would be a different system, requiring the neutrals to be distinguished from the first system.

In this case, the industry norm is to use white for the 208/120 system and gray for the 480/277 system.
***

Another example would be a 60 Hz system and a 400 Hz system.
***

Would a normal power source need to be distinguished from a UPS source? It would seem to me that it should be, but I don't know how others may view it.

How about generator wiring vs normal power wiring?

Opinions?
 
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