6

My 50s era ranch home is wired using cloth-covered NM, as you can see in these photos (taken in a basement closet located under the stairwell where the NM is run exposed): DIAMOND DTX TYPE NM 14/3

Should I be suspicious of this wire, or is it still good for a significant service life? Also, will I have to pull an outlet or switch to tell if it carries a ground wire, or is that ruled out by the age of this cable? Was cloth-jacket NM ever made with a ground wire?

2

My house had a fair bit of that wiring. It was apparently available both with and without ground but the ungrounded type is all I have ever seen.

If you arent doing any work on it its probably fine to just leave it alone. If you start doing significant rewiring, adding outlets, or any of the cloth is damaged, its probably time to run new cable back to the electrical panel. In my case, the cloth on most of it had become very brittle and started to flake off if it was moved too much, so if rewiring things I would replace it.

I have slowly replaced most of it in my house when convenient - when we were renovating and had the walls opened up anyways, mostly to get proper grounds everywhere.

3

The conductors and the insulation inside the jacket are almost certainly perfectly okay.

The only worrisome thing that comes to mind is that the ground wires in those old NM cables, when they had ground wires, were generally undersized relative to the primary conductors.

The electrical code requires that you bring anything you touch during a remodel up to the current code.

The current code basically requires that the ground wires be the same gauge as the primary conductors (#14 for 15A circuit, #12 for 20A circuit, etc).

I don't know if there's an exception for this old cable.

  • ...and #10 for 30A. So many in the field try to avoid that one. – ChiefTwoPencils Jan 13 '15 at 0:11
  • @ChiefTwoPencils I once saw 14-2 NM/Romex running from a 30A two pole breaker through joists, then through a stretch of metal conduit to an electric water heater... – Craig Jan 13 '15 at 0:15
0

You can rest easy - there's nothing wrong with the wire. The important thing is that all your electrical system is properly connected and grounded.

I've seen this wire in both 2 conductor (plus ground) and 3 conductor (plus ground). The newer cables have plastic sheathing which is easier to pull when you're pulling wires through studs/joists, etc, but there is no reason to replace this wire if you don't need to do so.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.