Grounded Conductor

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porterh

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Maybe someone can help me. Where in the N.E.C. does it mandate that a branch circuit supplied with type NM cable, the grounded conductor has to be insulated. A person ran a branch circuit an used the bare ground conductor as a grounded conductor. I know about 250. 140(3), but past that where does the N.E.C. mandate insulation on the grounded conductor for a branch circuit?

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Porterh
 
porterh said:
Maybe someone can help me. Where in the N.E.C. does it mandate that a branch circuit supplied with type NM cable, the grounded conductor has to be insulated. A person ran a branch circuit an used the bare ground conductor as a grounded conductor. I know about 250. 140(3), but past that where does the N.E.C. mandate insulation on the grounded conductor for a branch circuit?

Thanks
Porterh
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210.5(A) refers you to 200. 6

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As a practical matter, if you have an uninsulated grounded conductor and either a metallic raceway or uninsulated EGC, there is no practical way to insure that there will not be an extra ground to neutral bond, in violation of the NEC.
And using an uninsulated ground and an insulated EGC just seems wrong somehow and likely to lead to confusion and incorrect device installation.
 
Now I really don't know, 200.2(A) says where insulated, where insulated does not sound to me like shall be insulated but like gold digger said how would we keep from getting the two confused

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Maybe 334.112. EGC's are permitted to be bare by 334.108.

III. Construction Specifications

334.112 Insulation. The insulated power conductors shall
be one of the types listed in Table 310.104(A) that are
suitable for branch-circuit wiring or one that is identified
for use in these cables. Conductor insulation shall be rated
at 90°C (194°F).
Click to expand...

334.108 Equipment Grounding Conductor. In addition
to the insulated conductors, the cable shall have an insu-
lated, covered, or bare equipment grounding conductor.
Click to expand...
 
wwhitney said:
Maybe, but I don't think so. 334.112 doesn't actually tell you all the power conductors have to be insulated. It just imposes conditions on the insulated power conductors.

Cheers, Wayne
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The CMP was possibly thinking ungrounded when they said insulated?
Clearly ungrounded conductors need to be insulated, but where is that even stated?
I suspect that the sections cited so far are worded that way to avoid banning SE type cables, which may have at most an overall covering, not insulation, over the grounded conductor.
 
By definition all of the conductors are required to be insulated, EGC's have special permission to be bare. :D

334.2 Definitions.
Nonmetallic-Sheathed Cable. A factory assembly of two
or more insulated conductors enclosed within an overall
nonmetallic jacket.
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To make this a little more plausible, suppose we have a 120V circuit in a single family residence wired with NM cable. Part of the wiring requires 4 ungrounded conductors for switched loads, etc., plus the grounded conductor and the EGC. All that is on hand is 12/2 NM, and 300.3(B)(3) allows the circuit conductors to be split up into multiple runs of cable (preferably following the same path). Can this be wired as two runs of 12/2 NM, using one of the bare wires as the EGC, the other as the grounded conductor? Assume the boxes are non-metallic and care is taken to avoid accidental contact between the bare conductors in the boxes.

Cheers, Wayne
 
infinity said:
By definition all of the conductors are required to be insulated, EGC's have special permission to be bare. :D
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I don't think the omission of something in the 334.2 definition precludes its presence in the cable. For example, the paper wrapper in NM cable is mentioned nowhere in the definition, does that mean it is not allowed there? I see 334.108 as confirmation of this, in that it refers to the possibility of an uninsulated EGC, which isn't mentioned in the 334.2 definition. The definition of tray cable in 336.2 is clearer, so I think the 334.2 definition is just sloppy.

Even if you read article 334 to require that any non-EGC conductor in NM cable needs to be insulated, what about smurf tube? Suppose I have a house with a panelboard in a non-metallic enclosure and circuits run in smurf tube to non-metallic boxes. Can I use a bare conductor for the grounded conductor, and a green insulated conductor for the EGC?

Cheers, Wayne
 
wwhitney said:
I don't think the omission of something in the 334.2 definition precludes its presence in the cable. For example, the paper wrapper in NM cable is mentioned nowhere in the definition, does that mean it is not allowed there? I see 334.108 as confirmation of this, in that it refers to the possibility of an uninsulated EGC, which isn't mentioned in the 334.2 definition. The definition of tray cable in 336.2 is clearer, so I think the 334.2 definition is just sloppy.

Even if you read article 334 to require that any non-EGC conductor in NM cable needs to be insulated, what about smurf tube? Suppose I have a house with a panelboard in a non-metallic enclosure and circuits run in smurf tube to non-metallic boxes. Can I use a bare conductor for the grounded conductor, and a green insulated conductor for the EGC?

Cheers, Wayne
Click to expand...


Seems to me like you're off on a tangent. Doesn't 334.2 tell you that the conductors in NM cable are insulated?
 
infinity said:
Seems to me like you're off on a tangent.
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Well, the reason for the smurf tube question is that one would expect there to be some general language requiring grounded conductors to be insulated, with exceptions for SE cable. If such language is in the NEC, nobody has come up with it. But if you'd like to stick to NM cable we can, that was the OP's question.

infinity said:
Doesn't 334.2 tell you that the conductors in NM cable are insulated?
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I don't read it that way, it is silent on whether anything else is in the "overall non-metallic jacket" besides the "two or more insulated conductors". Obviously something else is in there, the bare conductor and the paper wrapper.

Also, in general I don't see non-definition code sections as able to modify definitions. Rather 334.108 is referring to a possibility that the definition already encompasses.

Cheers, Wayne
 
The OP stated NM cable so I'll stick with that and remain on topic.

The one sentence definition of NM cable is pretty clear to me so there is no need to read anything more into it. It states "A factory assembly of two or more insulated conductors", that's it. If it's NM cable constructed according to Article 334 the conductors are insulated.
 
infinity said:
The one sentence definition of NM cable is pretty clear to me so there is no need to read anything more into it. It states "A factory assembly of two or more insulated conductors", that's it. If it's NM cable constructed according to Article 334 the conductors are insulated.
Click to expand...
Yet the EGC is uninsulated and it is a conductor, so it can't be that simple. The options are:

a) The definition allows other (uninsulated) conductors in the cable.
b) Article 334.108 modifies the 334.2 definition to allow an uninsulated EGC.

I'll take option (a), it is more logical, for the reasons I've stated previously.

Cheers, Wayne
 
infinity said:
The OP stated NM cable so I'll stick with that and remain on topic.

The one sentence definition of NM cable is pretty clear to me so there is no need to read anything more into it. It states "A factory assembly of two or more insulated conductors", that's it. If it's NM cable constructed according to Article 334 the conductors are insulated.
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And therefore the EGC is not a conductor?
The fact that the is described elsewhere as a component that can be uninsulated does not make it any less a conductor.
 
GoldDigger said:
And therefore the EGC is not a conductor?
The fact that the is described elsewhere as a component that can be uninsulated does not make it any less a conductor.
Click to expand...

If it is made out of an elemental form of anything to the left of the zigzag line on the periodic table, IT IS A CONDUCTOR. Last time I checked, a bare wire in a cable assembly is made from either copper or aluminum, both of which are to the left of that zigzag line.
 
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I've got to agree with infinity on this one.

You are required to use a recognized wiring method. 334.2 specifies that NM cable consists of insulated conductors. If you're going to use NM as a wiring method that is what you have to use. 334.108 adds the requirement for an equipment ground and makes the allowance for it to be bare. There is no allowance that I can see for the other conductors to be bare.
 
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