Knob and Tube in attic / insulation

Discussion in 'Electrical Forum discussion & Blog' started by The old college try, Feb 2, 2008.

  1. The old college try

    The old college try Engineering Technician

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    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: Feb 2, 2008
  2. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

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    I would, but let's wait for a real pro's opinion...
  3. Cass

    Cass Plumber

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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. The old college try

    The old college try Engineering Technician

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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. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

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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: Feb 4, 2008
  6. The old college try

    The old college try Engineering Technician

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    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: Feb 3, 2008
  7. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

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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.
  8. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

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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
  9. frenchie

    frenchie Jack of all trades

    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.

    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.

    Attached Files:

  10. The old college try

    The old college try Engineering Technician

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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.
  11. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

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    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.
  12. Nate R

    Nate R New Member

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    Mikey, how do you ID every outlet? Do you put a number on them?
  13. Ian Gills

    Ian Gills Senior Robin Hood Guy

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    Labelling on the panel is only supposed to be indicative.
  14. The old college try

    The old college try Engineering Technician

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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?
  15. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

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    Yes it probably should have. I would have at least. Does it at least have a GFCI?
  16. The old college try

    The old college try Engineering Technician

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    Yeah, I was happy to see that the breaker was a GFCI.
  17. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

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    I did until She Who Must be Obeyed opined that it looked dorky. Now they're identified by area/location -- e.g., kitchen/N wall, 3rd receptacle. Or Hall/ceiling cans. This means, of course, you often need to have the cross-reference in your hand to identify things, but it turns out not to be a problem.

    Every inspector who's seen my panel has said he wished they were all that detailed. I've said the same thing when called to work on one of the "Plugs" and "Lights" style...
  18. lampman42

    lampman42 New Member

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    Labeling Receptacles

    I like the spreadsheet idea very nice, I think I will do the same.

    As for labeling them I did work in a hospital and they had all the recep covers marked with the circuit number on the back of the plate with permanent maker. This may be a good alternative to marking on the outside.

    And the panel schedule wasnt all that bad most panels are pretty bad and you are lucky if there is a marking at all.

    Once again kudos to the spreadsheet idea. Why didnt I think of that?
  19. The old college try

    The old college try Engineering Technician

    Messages:
    104
    Location:
    MO
    So, I went up this evening now that I have all of the fiberglass removed from the area and I mapped out the old wiring. I think my next step is to pull off the switch plates and see if the old wires and entering those locations. If so, hopefully I can run new switch wires up to the attic and disconnect the old junk. I'll probably have to put a junction box where the old wires come up out of the exterior wall. I'm annoyed that I'm getting false readings on my non-contact tester. I tested it on a wire that not connected to anything on either end and it's reading voltage in the line, so I can't trust it.

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  20. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

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    What are red vs black?
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