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Thread: Knob and Tube in attic / insulation

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  1. #1
    Engineering Technician The old college try's Avatar
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    Default Knob and Tube in attic / insulation

    I'm doing some work in my attic to upgrade insulation. I'm pulling up the existing insulation as I go to ensure that there are no problems. I'm coming across alot of old knob and tube wiring, alot of which has been disconnected, and new wiring has been run all over. There are a few places where the wiring disappears down through the ceiling. I'm guessing that these wires are no longer live, but I want to be sure before I add new insulation. What's the best / easiest way to test these old wire to ensure they have been disconnected? I plan on removing any old wiring I find to leave no doubt for the next guy that owns this 80 year old ramshackle. Can I trust a non-contact voltage detector?
    Last edited by The old college try; 02-02-2008 at 08:19 PM.

  2. #2
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    I would, but let's wait for a real pro's opinion...

  3. #3
    Plumber Cass's Avatar
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    Generally they can be trusted as long as they are tested before each use.

    The only thing I would be careful about is cutting 1 leg of a 3 way switch that happens not to be energized, or even a regular switch for that matter.

    Lets see what the sparkys have to say.

  4. #4
    Engineering Technician The old college try's Avatar
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    So, I was all excited to get up in the attic and do my insulating before I came across this K&N wiring. I tested the wires (blacka and white) with a non-contact testor and the tester is lit up like a christmas tree on all of the wiring. I thought that it would all be dead since someone ran new wiring all over in the past. Needless to say, I'm completely limp. Since many of the wires disappear into the floor, I'm not sure how to proceed.

  5. #5
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    If you've got new wiring, odds are you've got a relatively modern service entrance panel, with circuit breakers. With you in the attic, and your lovely assistant (you do have a lovely assistant, don't you?) at the panel, have her turn off the circuit breakers one at a time until your K&T circuit goes dead. Repeat for all K&T segments you can find. That will identify the circuit(s) that are associaed with the K&T wiring. Then it's a matter of tracing each of the "bad" circuits to see where the K&T segment(s) are.

    It'd be nice to say "then replace them", but if they weren't all replaced when the new wiring went in, there was probably a reason. If it was just because the previous owner or electrician was lazy or ran out of money, you're OK, since you're ambitious and flush. If replacing the K&T is going to involve some serious demoliton, that's another story.

    Having said that, another alternative is to just go ahead and add the new insulation, perhaps posting a sign in the attic to warn future attic-crawlers of the danger hidden under the insulation. Be sure to use non-conductive insulation, but I can't think of any that is (conductive), offhand.
    Last edited by Mikey; 02-04-2008 at 04:00 AM.

  6. #6
    Engineering Technician The old college try's Avatar
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    Default She's lovely.

    She's lovely alright. Thanks for the advice. Is it possible to mistake a wire being dead by having a switch turned off somewhere, or will it typically be energized always? Also, I just went around and tested every receptacle in the house and they all have grounds. Am I correct in thinking that all of these have been re-wired and the live knob and tube is probably being energized by a light or from a switch?
    Last edited by The old college try; 02-03-2008 at 08:41 PM.

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