Old wiring, should it be replaced?


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Old 03-22-17, 09:38 PM
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Old wiring, should it be replaced?

Just wanted to get some opinions from electricians/electrical experts.

My home was built and wired in 1939. Most of the main floor living areas still have the original wiring. The wiring is a cloth covered NM cable with no ground. (It is NOT knob and tube, though.) However, inside the outer sheath of insulation, only the hot wire has its own insulation. The neutral is a bare stranded wire that is wrapped around the hot wire.

I have some samples of this wiring that are from circuits that were replaced with modern wiring. If the outer sheath is removed, the insulation on the hot wire is intact. However, if the hot wire is then bent back and forth 90 degrees a few times, sometimes (but not always) the cloth braid splits at the bend and the insulation underneath falls off/crumbles and metal can be seen. Sometimes this happens even if the wire is bent 90 degrees just once. If the hot wire is bent in more than one place at the same time (which is likely to happen if a device is pushed back into a box), then the braid usually splits at the bends and insulation crumbles and falls out. Interestingly, though, if the cable is bent with the outer sheath still on it, then the outer sheath is removed afterwards, the hot wire's insulation does not seem to be affected.

Do you think the original wiring needs to be replaced soon to avoid a fire hazard from arcing? (Especially since the neutral is bare.) I would have an electrician do this, I wouldn't be doing it myself. The walls will not be gutted. However there is attic access. There is also basement access, with half the basement having an unfinished ceiling and the other half having a junky ceiling made of nailed on ceiling tiles that are falling apart and could be ripped out and replaced. (There is only one story of living space.)

Thanks in advance.
 
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Old 03-22-17, 10:05 PM
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Sounds almost like SE cable not NM. Is there any legible writing on the sheath. Can you post pictures? http://www.doityourself.com/forum/li...rt-images.html
 
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Old 03-23-17, 08:15 AM
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Please provide some pictures as that is a very unusual cable.

Yes, you should have this replaced but hard to say what the urgency is. For now don't use any high wattage appliances like space heaters. As you found out the issue is mainly where the wires are disturbed. Other issue identified is heat as 100 watt bulbs would bake the old insulation. Whenever doing any changes shrink wrap can be pushed over the conductors where accessible.

Found one other reference: What the?!??!??! - Electrician Talk - Professional Electrical Contractors Forum
 
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Old 03-23-17, 12:28 PM
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Interesting in Astuffs' link they are guessing SE same as I did. I'm wondering if that was ever code compliant. I would definitely replace if I could afford it or at least install AFCI protection to reduce the chance of fire from arcing.
 
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Old 03-23-17, 12:34 PM
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I've seen a lot of cloth-covered NM, but never quite like you describe. In general, the cloth-covered wiring is still servicable as long as it's not touched or moved very much. As you've noticed the covering does get brittle.

I think more of the issue is it being ungrounded. It may not need immediate replacement, but to remain current, grounds (and likely more circuits) are probably needed. Older houses are often wired with one or two circuits covering all the receptacles. Which is woefully insufficient for today's houses.

I too would consider replacement, even if it's a bit at a time.
 
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Old 03-23-17, 02:06 PM
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I found one picture of what I think he's talking about but nobody there can remember what it's called. It's definitely not SE.

 
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Old 03-23-17, 08:38 PM
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Definately not from the service entrance, as it attaches to the receptacles, switches, and light fixtures. There are no labels on the cloth, but the stripped wire appears to be 14 AWG (appears to be same size as stripped 14 AWG wire.) It looks like the picture in the link posted by Astuff. I can try to get a picture tomorrow.


The service entrance, grounded appliances (laundry room, microwave, refrigerator, gas furnace fan, one outlet in the room w/computer) and the outlets in the bathroom and basement were wired in the past 2 - 35 years and are all grounded, modern wiring. The central A/C wiring was wired in the 60s and is not cloth covered and is grounded through a metal conduit. But the rest is the original 1939 wiring. (There are no 240V citrcuits except for the central A/C.)
 

Last edited by Franklin1975; 03-23-17 at 08:49 PM. Reason: typo
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Old 03-23-17, 11:13 PM
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This is the cable when the outer sheath is removed. (Pinky finger for scale.) The neutral's strands are seperated and wrapped around the outside of the insulated hot wire.

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This is the cable with the neutral's strands unwrapped from the hot wire and twisted together, like they are inside boxes.

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Old 03-24-17, 07:21 AM
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You are showing me something I have never seen, even in very old buildings.
 
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Old 03-24-17, 10:28 AM
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That is something unique. The outer is not braided but I would still call it SEU single conductor or coax NM.

Thanks for sharing those pictures.

Something to research if someone has a 1930's NEC.
 
 

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