What Came After Knob and Tube Wiring???

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  #1  
Old 09-11-13, 09:04 AM
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What Came After Knob and Tube Wiring???

Hello there! I have been upgrading wiring as needed when I do home renovations. I have a 1900 Colonial that did not have electricity when built....so there are many generations of wiring in my house.

There was one section of knob and tube in my basement...and now it is gone. The rest is either 14-2 or 12-2 of varying ages.

But I have one older circuit that is strange to me. It is two wires, a hot and a neutral that have their own insulated jacket. Similar to knob and tube.....but without the knob and tube.

The two individual wires are routed through the walls loosely much like modern wiring. The insulation jacket is fairly thick in diameter for the #14 wire inside....I'd say the jacket is 3/8 or 1/2 thick overall.

Any guesses?
 
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Old 09-11-13, 09:50 AM
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That still sounds like a type of knob and tube.

After k and t I think they went to a two conductor cloth covered cable.
 
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Old 09-11-13, 10:09 AM
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After k and t I think they went to a two conductor cloth covered cable.
I have seen a lot of the very old cloth covered cable in past years, but I am not sure if it came before or after the early steel BX wiring. Could be they both came about the same time.
 
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Old 09-11-13, 10:24 AM
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After k and t I think they went to a two conductor cloth covered cable.
Yup....in one sentence this explains what I was trying to describe. But my next question....is there anything inherently dangerous?

K and T obviously has its drawbacks because bare wires clearly pose a problem, or even wrapped K and T. But what about the cloth covered stuff?

More or less safe if left undisturbed....just ancient and replace it if you can?
 
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Old 09-11-13, 10:35 AM
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More or less safe if left undisturbed....just ancient and replace it if you can?
That about sums it up.



AC(BX) Armor clad cable BX is the common trade name for AC. BX was the trademark of cable made by G.E.'s Sprague Electric division.
189?- Gus Johnson and Harry Greenfield patent AC
1910- AC receiving acceptance.
1920s or the early 1930s widespread adoption.
1932 NEC- Armored cable was officially called Type AC
1952- Aluminum clad AC introduced.
1959 NEC- Aluminum bonding wire required under metal sheathing.

After K&T, they invented multi-conductor cable. The first type you will see is roughly a cloth and varnish insulation. It looks much like the romex cable of the last decade or two. This stuff was used in the 40's and 50's. Again, no grounding conductor. It was installed much like modern wiring. Its major drawback is that this type of insulation embrittles.

Thanks to Lisa at the DIY chatroom for the above info.
 
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Old 09-11-13, 10:55 AM
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Thanks for the info! My only reason for concern is that our house just had insulation blown in a few months ago. At the time they asked...do you have K&T? A reasonable question. Obviously....potentially damp cellulose across two bare conductors = BAD!

I am 100% sure I don't have K&T. I thought this "individual cloth wrapped two conductor" was isolated to the 1st floor dining room of the house.

It turns out it branches into the bedroom above it. There are two sockets on an outside wall that have this type of wiring.

Any reason to be concerned? As long as the insulation was is intact and they weren't animals blowing the insulation in....I'm thinking things should be fine right.

What do you think?
 
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Old 09-11-13, 01:07 PM
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Obviously....potentially damp cellulose across two bare conductors = BAD!
Bad yes but not for either of those reasons. The wires aren't bare. They are insulated and water isn't really the problem. The wires are designed/rated to be installed in free air to dissipate heat. In insulation they can overheat.
 
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Old 09-12-13, 04:53 AM
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Very good point! We don't use these sockets for anything other than an alarm clock and a window fan so I feel somewhat safe. I plan on renovating that room sooner or later so I'll replace the circuit. I'm sure the next owner of this home would appreciate it.

But I have another question. What is the difference between not having an air gap for this older wiring with blown in insulation......and modern 14-2, 12-2, etc that is surrounded by blown in insulation?

I'm sure its okay as there are a zillion homes out there with blown in insulation. I'm just curious.
 
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Old 09-12-13, 05:46 AM
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What is the difference between not having an air gap for this older wiring with blown in insulation......and modern 14-
Some say it is insurance company hype. They point out #14 copper wire is limited by code to 15 amperes but if you check you will find that rubber-insulated #14 can actually handle 30 amperes as a single wire in free air. No #14 copper wire, regardless of the insulation type or if it is a cable or single wire is going to be releasing much heat to the ambient area at 15 amperes or less. In all fairness to cable though two wires in a raceway heat less because the electromagnetic fields cancel each other or so they say and current code requires they be in the same raceway. Your decision but remember what the insurance company may say if there is a fire even if it isn't really related to the K&T.
 
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Old 09-12-13, 07:21 AM
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What is the difference between not having an air gap for this older wiring with blown in insulation......and modern 14-2, 12-2, etc that is surrounded by blown in insulation?
The further apart the two separate K&T conductors are, the greater the amount of inductive heating that is present. In addition, blown in insulation sometimes causes two separate K&T conductors that possibly aren't tightly secured to be pushed together (especially in walls) and can cause a direct short igniting a fire. My opinion is this; the older wiring with blown insulation is a fire hazard and the modern NM cables in blown insulation are not.

I'm sure its okay as there are a zillion homes out there with blown in insulation.
You are right, there are a lot of homes out there with blown insulation, but they don't all have K&T wiring. There is a good reason the insulators asked you if you had K&T wiring, the statistics show the risk of fire is dramatically increased.
 
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Old 09-12-13, 12:37 PM
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The further apart the two separate K&T conductors are, the greater the amount of inductive heating that is present.
Only to a degree and while this IS important with power conductors the inductive heating on a 15 ampere branch circuit is negligible.

In addition, blown in insulation sometimes causes two separate K&T conductors that possibly aren't tightly secured to be pushed together (especially in walls) and can cause a direct short igniting a fire.
Two K&T conductors that would be loose enough to be pushed into contact would not be properly installed without insulating loom on the wires. Assuming a total breakdown of the wire's insulation AND the thermal insulation pushing the conductors together is a lot of assuming. My opinion is that type NM cable is as likely to be punctured by an errant nail or screw as any problem with properly installed K&T such as you have described.


In my opinion the biggest problem with K&T is that it was protected by screw-base fuses and it was far too easy to install a 30 ampere fuse on a #14 conductor circuit.
 
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Old 09-12-13, 03:34 PM
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K and T obviously has its drawbacks because bare wires clearly pose a problem, or even wrapped K and T. But what about the cloth covered stuff?
The wires - individual conductors - used for K&T wiring are not bare. They are insulated by rubber and cloth. K&T is still usable and may be kept in service so long as it is left undisturbed and in dry air.

It's the "dry" in the dry air requirement that's important. That's why K&T can't be covered with insulation.

In 1983 I began renovating our 1908 house. It had gas-electric lighting when it was built. The house was fed with a single piece of 14-2 NM from the fusebox. All of the other wiring was K&T. Within a week or so it had a new 200A service, two new subpanels, more than 1,000' of new Type NM with a grounding conductor, etc. When I finished, there were two K&T runs still in place. I took the inspector everywhere, and showed him the working K&T. The house passed final with flying colors, and that wiring was still in place, and still in service, when I sold it 15 years later.

Because there's no grounding conductor present, a circuit that ends with either K&T or early Type NM (the "cloth covered stuff") cannot be extended.

But I have another question. What is the difference between not having an air gap for this older wiring with blown in insulation......and modern 14-2, 12-2, etc that is surrounded by blown in insulation?
The reason for the air for K&T has been explained above.

I'll assume that when you ask about "14-2, 12-2, etc" you're asking about Type NM cables, not Type AC or MC. There is a similar requirement limiting the number of Type NM cables that may be run together through an insulated space.
 
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Old 09-13-13, 06:27 AM
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Two K&T conductors that would be loose enough to be pushed into contact would not be properly installed without insulating loom on the wires. Assuming a total breakdown of the wire's insulation AND the thermal insulation pushing the conductors together is a lot of assuming. My opinion is that type NM cable is as likely to be punctured by an errant nail or screw as any problem with properly installed K&T such as you have described.
My opinion is based upon personal experiences of many years ago. If K&T wiring were to remain in pristine condition, as good as the day it was installed, I would have to agree, but the fact is that it many times doesn't. Attics get used for loose storage and K&T wiring gets disturbed. 40 years ago DIY homeowners started getting concerned about utility bills as rates began rising and started insulating attics by shoving batts of insulation under the K&T wiring. In my own experience I have seen K&T conductors laying loose on top of insulation batts. I have also seen K&T conductors laying loose on top of plaster lath in uninsulated attics. Walls were opened by DIY renovations and the K&T conductors were pushed this way and that way for insulation to fill the wall cavities. The point is, K&T is fine as long as it is never disturbed and remains pristine, but many times it does get disturbed by unknowing DIYers who do whatever they have to do to get their insulation in place. As far as blown insulation in walls, there is a reason the insulators ask about K&T wiring. I have seen a few cases of fires igniting in walls originating from K&T wiring after cellulose was blown in. Was the K&T installed properly when the old house was framed, I didn't know. Was the K&T previously disturbed, I had no way of knowing, but the fact is, it sometimes does happen. My opinion is it's best to replace K&T wiring in many cases, but if it has remained in pristine condition and is not subject to damage, it could last a long time.
 
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Old 09-13-13, 10:49 PM
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if it has remained in pristine condition and is not subject to damage, it could last a long time.
Note that that means the K&T conductors are not in contact with insulation, anywhere.
 
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