# For the old-timers here... What's that old wire?



## steve-in-kville (Aug 30, 2006)

What was the name of that old wire I tear out of places... its like THHN, two individual conductors with this thick, black fabric-like insulation. Looks to be about a #14 wire. I'm sure it was pre-romex stuff, but I am curious if it actually has a name.

Also- I once found old ceramic insulators nailed to the joists in a basement where bare wire once was used. 

If anyone remembers actually installing and maintaining these old systems, I'd like to hear about it. If anyone could date this stuff, it would be interesting to read.

Thanks!

steve


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## mdshunk (Mar 13, 2005)

It's called "knob and tube"

The system was a rubber insulated wire, with a cambric woven outer jacket. 

It used porcelain "knobs" or "spools" to support the wire where it runs parallel to the joists. It used porcelain "tubes" where it passses through bored holes perpendicular to joists. It used woven fabric "loom" to sleeve the conductors where they're fished in walls, and at entrances into boxes. Wall boxes had internal "loom clamps", similar in appearance the internal box romex clamps. Where these single conductors entered a box with the typical knockouts, a porcelain "federal bushing" was used in the knockout.

This type of system was necessarily ungrounded. It is 100% legal, just old. I run into this system nearly every single day.


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## mdshunk (Mar 13, 2005)

Matter of fact, PPC still makes that crap....


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## steve-in-kville (Aug 30, 2006)

So that's whats meant by Knob and Tube? I heard the term before, but never knew exactly what it was. Does anyone know when the modern romex w/ground started becoming popular? I'm not quite 30 y/o and this info really helps me date some of the previous "upgrades" I see in homes.

steve


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## mdshunk (Mar 13, 2005)

Well, first was mostly knob and tube. Then, there was a braided fabric jacket romex with paper interleaving with no ground wire. (This stuff actually was worse than K&T, since it didn't handle the effects of heat as well.) Then, there was thermoplastic sheathed romex with no ground wire. Braided romex still co-existed. Then there was romex with a reduced size ground. This existed in braided and thermoplastic sheathed version. About 1967-8, the full transition was mostly made to only thermoplastic sheathed romex with a full sized ground. All versions before that overlapped and co-existed for so many years, that it's hard to pin down the exact vintage.


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## R&S Exteriors (Aug 4, 2006)

There is still boo-coo knob & tube and braided here in central PA. I'm not sure how some of these houses with 60 amp service and everything running on 4-6 fuses don't burn down with the amount of electricity an average home uses these days.


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## steve-in-kville (Aug 30, 2006)

Thanks for the info! I've found that older fabric jacket romex already. 

BTW- I see you're in Pa. Which county? I'm in Lebanon.

steve


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## mdshunk (Mar 13, 2005)

steve-in-kville said:


> BTW- I see you're in Pa. Which county? I'm in Lebanon.


Yeah, I love your balonga.

I work primarily in Franklin, Cumberland, Fulton, and Adams counties. Dauphin a little.


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## mdshunk (Mar 13, 2005)

R&S Exteriors said:


> There is still boo-coo knob & tube and braided here in central PA. I'm not sure how some of these houses with 60 amp service and everything running on 4-6 fuses don't burn down with the amount of electricity an average home uses these days.


You got that right. I've got a service upgrade scheduled where the house still has the original 30 amp, 120 volt service. The service equipment consists of an OLD 'A' base meter on the porch, and a porcelain open knife switch for a disconnect, and one porcelain edison base fuse holder.


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## steve-in-kville (Aug 30, 2006)

Okay, so you're from out towards the Carlisle area. I once worked for a large electrical contractor and we did a bunch of jobs out that way.

steve


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## reveivl (May 29, 2005)

I found one of the 'knobs' once that was through a beam, it was about 8" long. So I guess they made them for all situations. I use it to hone my knife. The electrician I use says that it was actually a good system with the seperate hot line. Except for the lack of ground. R.


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## mdshunk (Mar 13, 2005)

reveivl said:


> I found one of the 'knobs' once that was through a beam, it was about 8" long. So I guess they made them for all situations. I use it to hone my knife. The electrician I use says that it was actually a good system with the seperate hot line. Except for the lack of ground. R.


Yeah, those tubes came in all different lengths. I thought once about saving some of the more odd or cherry ones when I do re-wires, but I'm not sure what the heck I'd do with them. They're not worth crap, really. 

Yeah, it was a pretty decent system. It held up fine through the years. The trouble comes from where people have 'messed" with it, doing taps in a non-compliant manner and otherwise abusing it.


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## Joasis (Mar 28, 2006)

I have seen a ton of this stuff, but after reading your last post, now I am curious. So what was the correct method to tap off the lines when it was needed? I remember seeing one where the wires were just twisted around the "lines" for a drop to an outlet. My own home still has this system in the attic and will come out someday...mainly since I need to add more insulation and this stuff is bare and dangerous looking.


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## mdshunk (Mar 13, 2005)

joasis said:


> ...mainly since I need to add more insulation and this stuff is bare and dangerous looking.


Bare, really? In any event, the K&T must come out if you intend to insulate. Walls too. Knob and Tube relied on being in free air for cooling. It WILL OVERHEAT if you insulate it. It is not permissable to insulate a wall or ceiling cavity that has knob and tube wiring running through it. I try not to be an alarmist, and seldom use the phrase "It will burn your house down", but insulating knob and tube is a potential fire hazard. I know you're gonna remove it first, but I never miss an opportunity to point this out. 

Any tap onto knob and tube must be done by mechanical means. Just wrapping the tap around the run, or soldering the wire does not meet code and is therefore not safe. A mechanical connection (such as a little copper #14 split bolt) is the only compliant method. If the tap conductors are part of a romex cable, you need to use a rather hard to find fitting on the romex called an "End-o" or "monkeyface" connector.


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## Jim Garcia (Aug 31, 2006)

THe cool thing about knob and tube is that at one time it was *state of the art* stuff.


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## JoeTedesco (Sep 3, 2006)

UL still lists "Flexible Tubing" we called it "Loom"

The other point that should be mentioned is that "rubber" insulation will eventually become a problem.

The NEC had a FPN that covered this and was located in Article 310.

In another Note 2 the NEC showed where it was OK to protect K&T at 20 Amps.

See the 1965 and earlier editions of the NEC. I believe that NFPA still stocks the old codes from the 1975 edition through the present.


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## PipeGuy (Oct 8, 2004)

mdshunk said:


> ...Then, there was a braided fabric jacket romex with paper interleaving with no ground wire.


Sparkies- when you encounter degraded insuation in an old box, how do you remedy it?

My mom's house was built by a couple of bachelor farmers in the early 40's and is done completely in BX that has cloth/paper insulated conductors. Just the movement of pulling a wall switch or duplex from the box causes the insulation to crumble. My mom's always been a die-hard DIY'er and I've often wondered if the old house'll burn down someday because of something she neglected to attend properly.


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## mdshunk (Mar 13, 2005)

PipeGuy said:


> Sparkies- when you encounter degraded insuation in an old box, how do you remedy it?


At present, there is no repair system that is specifically trageted toward repairing degraded insulation on conductors in a box. I have repaired this type of degredation/damage in several different ways, which I will neither share or admit to having done. The only 100% compliant option is to replace the degraded cable or conductors.


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## PipeGuy (Oct 8, 2004)

mdshunk said:


> ...I have repaired this type of degredation/damage in several different ways, which I will neither share or admit to having done.


MD, I do beleive Diogenes' fruitless search may have been otherwise succesful had he but stumbled upon your doorstep, lantern in hand.


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## mdshunk (Mar 13, 2005)

PipeGuy said:


> MD, I do beleive Diogenes' fruitless search may have been otherwise succesful had he but stumbled upon your doorstep, lantern in hand.


I have no idea what you're talking about, but I'm glad you feel that way. (I guess?)


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