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Thread: Knob and Tube in attic / insulation

  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.

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    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...

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    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.

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    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.

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    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.

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    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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    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    You're close. The wire must be energized, but current need not flow, for the non-contact gizmo to say "live" on the ungrounded conductor (black, aka "hot"). I'm not sure if the gizmo will ever say the grounded conductor (white, aka "neutral") is live even if current is flowing, but I'm sure someone else knows. I think not, but will experiment today. I think you're probably right, that they elected to rewire the receptacles, but skipped the lighting. Which wires are hot depends on how the lights and switches are wired.

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    I&C Engineer (mostly WWTP) Lakee911's Avatar
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    I had a few places that I couldn't replace the K&T without demo, so I put an electrical box over the hole where it disappeared into the wall and then just switched to romex and ran that to where ever it went. Did the same where it went down again.

    Jason

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    Jack of all trades frenchie's Avatar
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    Quote Originally Posted by The old college try View Post
    She's lovely alright. Thanks for the advice. Is it possible to mistake a wire being dead by having a switch turned off somewhere?
    Yes.

    If the switch is off, the wire from the switch to the light will seem dead; it'll only show up as live if the switch is turned on.

    Ditto the neutrals on a receptacle with nothing plugged in, or the neutrals from a light that's turned off or doesn't have a bulb in it.

    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?
    I wouldn't take it for granted. Someone may have run a separate ground wire. I've never dealt with k&t, but I have seen this in houses with cloth-wrapped 2-wire cable, where someone had obviously added the ground wire, later.
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    Engineering Technician The old college try's Avatar
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    So, when I came home from work today, I found that the breaker labeled "third floor bathroom, plugs on north wall in basement which includes fridge and answering machine", was tripped. This is what I'm dealing with. Who labels things like this in the panel??? Total bushleague. This breaker has tripped about 4 times in the last 3 years, and I find it too coincidental that it tripped a couple of days after I pulled insulation off of the old wiring. Now I'm nervous. I'm also nervous that some of the wires I found just laying there under the insulation had been previously broken off and pulled out of the ceiling leaving bare wires just hanging out in the walls. I think I'm going to go up and sketch up the wiring layout and try to figure things out. If I can't figure it out, I'll call in a pro.

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    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Quote Originally Posted by The old college try View Post
    ...the breaker labeled "third floor bathroom, plugs on north wall in basement which includes fridge and answering machine", was tripped. This is what I'm dealing with. Who labels things like this in the panel???
    That's actually pretty good, in my book. I usually see labels like "Plugs", "Lights", etc., if there are labels at all.

    At home, I identify every outlet and have a spreadsheet posted on the panel door that lists all outlets by breaker, and all breakers by outlet. Makes it easy to quickly see what breaker I need to trip to work on a specific outlet, and what other outlets will be affected when I do.

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    DIY Senior Member Nate R's Avatar
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    Mikey, how do you ID every outlet? Do you put a number on them?

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    Senior Robin Hood Guy Ian Gills's Avatar
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    Labelling on the panel is only supposed to be indicative.

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    Engineering Technician The old college try's Avatar
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    It would have been sweet if the downstairs refrigerator and answering machine were still there so I knew what they were talking about. Oh yeah, the bathroom was re-done sometime in the recent past. Shouldn't it have been put on its own circuit?

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    I&C Engineer (mostly WWTP) Lakee911's Avatar
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    Yes it probably should have. I would have at least. Does it at least have a GFCI?

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