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Thought I had a new type of wiring...


Richard Moore
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This threw me for a bit today. 1965 home with some older looking 14-2+g NM cable that had been split after entering the panel, but the split sheathing had been left in place. I had to look close to see that there actually was insulated conductors within the sheathing.

I have some other issues within the panel, but is there any harm in leaving the sheathing in place like this?

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My issue with that installation is that there would be less heat dissipating capability if the outer jacket remains. I assume there's a code prohibition against it, but, frankly, I don't know what it is. I've never seen anyone leave it in place. However, I think that given the fact that the breakers give off heat in an enclosed space it shouldn't be there.

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This threw me for a bit today. 1965 home with some older looking 14-2+g NM cable that had been split after entering the panel, but the split sheathing had been left in place. I had to look close to see that there actually was insulated conductors within the sheathing.

I have some other issues within the panel, but is there any harm in leaving the sheathing in place like this?

I've heard home inspectors and electricians both say that the sheathing shouldn't extend very far into the box but I've never heard them offer a code citation to back up the claim.

I just spent about 30 minutes combing through article 312 (cabinets, cutout boxes & meter socket enclosures) and article 334 (NM cable) and I can't find any prohibition against bringing the sheathing into the enclosure. If anyone ever hears of a code citation that prohibits this, please let me know.

There are two cables in there that look like UF, but UF shouldn't have any paper in it and Richard said that they actually said NM on them. I don't know what's going on with that.

- Jim Katen, Oregon

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There were actually 4 similar ones entering the panel, 2 at the other side. Circuits were all indoor (according to the labeling). Maybe just some early plastic NM?

I just spent about 30 minutes combing through article 312 (cabinets, cutout boxes & meter socket enclosures) and article 334 (NM cable) and I can't find any prohibition against bringing the sheathing into the enclosure. If anyone ever hears of a code citation that prohibits this, please let me know.

Yep, been there before with similar results. The heat dissipation concern doesn't actually make sense to this old head and I'm not going to call it. Because of other issues, the client is probably going to end up installing a new panel anyway to replace this old split-bus Bryant.

Y'know, I've done a bunch of wiring in the past but, thinking about it, I've never had to use any UF and never actually stripped any of it. Didn't realize it it was "tighter" than normal NM, although it makes sense thinking about it. May have to go buy a piece to play with.

Follow-up question if I may: If there are 8 throws in the main section of a split-bus panel, but 2 are unused (no wires connected), does that still meet the 6-throw disconnect requirement?

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This threw me for a bit today. 1965 home with some older looking 14-2+g NM cable that had been split after entering the panel, but the split sheathing had been left in place. I had to look close to see that there actually was insulated conductors within the sheathing.

I have some other issues within the panel, but is there any harm in leaving the sheathing in place like this?

I've heard home inspectors and electricians both say that the sheathing shouldn't extend very far into the box but I've never heard them offer a code citation to back up the claim.

I just spent about 30 minutes combing through article 312 (cabinets, cutout boxes & meter socket enclosures) and article 334 (NM cable) and I can't find any prohibition against bringing the sheathing into the enclosure. If anyone ever hears of a code citation that prohibits this, please let me know.

There are two cables in there that look like UF, but UF shouldn't have any paper in it and Richard said that they actually said NM on them. I don't know what's going on with that.

- Jim Katen, Oregon

I think that the answer might be found not in the code but in the UL listing regarding gutter space/fill limitations not having been calculated to include sheathing. That said, dammed if I could point you to an official source.

"Didn't realize it it was "tighter" than normal NM,"

Not tighter, the sheathing completely surrounds each individual conductor, separating each on from the other. They make sheathing strippers specifically for UF cable, without them it is a bastard to strip properly.

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  • 1 month later...

Romex and UF cable must have their outer jacket to extend into nonmetallic boxes at least 1/4" beyond any cable clamps. No code suggests the maximum distance that the outer jacket can enter into a non metallic box and there are no codes for minimum or maximum outer jacket lengths for metal boxes. NEC 314.17. No such codes exist for panels. However, 310.10 requires that conductors cannot be associated together where the limiting temperature of any of the conductors is exceeded.

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