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one of the cables going to our electrical panel uses silver color insulation ("silver cable" in picture below). I can identify all cables types on our panel except this one. When were these cables used? What is the type of insulation? I don't know the exact gauge but the ground wire from this cable is pretty small compared to modern 12/2 NM (see picture). Is this a potential concern?

Thanks!

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  • I've seen that cable in a house built in the 50's, but there are others with longer experience than me. Is there a chance the house, or a portion of it was rewired and that old cable was just abandoned there? Is it energized? Edit: I misread the question. Looks like the silver cable does go to the panel, you just don't know what type it is.
    – JPhi1618
    Dec 4, 2019 at 20:39
  • It's old but it will pass an inspection. Some advice, don't even touch it unless you are completely replacing it. In the past I've attempted to replace receptacles attached to that cloth jacketed cable and the wire just crumbles.
    – mreff555
    Dec 4, 2019 at 20:58

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That cable is old cloth jacketed nonmetallic cable. I would say by the 1970's, this was no longer being installed, nonmetallic cable in the 1970's had a plastic jacket not too much different than what's used today.

The ground wire was considerably smaller on the old cloth jacketed cable, and the early plastic jacketed cable. I see a lot of old 12-2 romex, which was white back then rather than yellow typical of 12-2 now, with a 16 gauge ground wire. The smaller gauge of the ground wire isn't usually an issue because it's usually not normally carrying current, it's intended to just carry fault current briefly so the breaker trips (or back then, the fuse blew). In some situations, the fault may not clear, and it's conceivable in those situations the wire could become overloaded, but that's unusual enough I don't think it's considered a major concern.

If the insulation is undisturbed, it's usually fine, but if it has deteriorated with age, it can be brittle and crumbly, so it's best left alone. It's especially prone to deterioration if it's been subjected to a lot of heat - in attics, above light fixtures, etc.

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    I've seen that cloth jacketed cable used from the 1920's to the 1960's. The insulation is typically cloth covered rubber. As @batsplasterson mentioned, the rubber gets brittle and crumbles with age. Even working around it, like pushing it aside to work on another wire, or vibration from a saw, can break the insulation. The wire is also likely smaller, made for lower current loads (e.g 14-16ga). If you have to work on it, it's best to just replace it. Dec 4, 2019 at 21:14

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