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Detecting Damaged Romex Cable Insulation

Discussion in 'Electrical Engineering' started by Home Builder, Mar 7, 2004.

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  1. Home Builder

    Home Builder Guest

    Background Scenario:

    Part 1) New house with 12-2 romex wiring installed by an electrician who
    often justified sloppy work with faulty assumptions. Regarding skimpy
    use of staples: "Them wires ain't going nowhere near the drywall screws
    but if the inspector says 'sumpin' we'll just tack up another staple
    here and there to keep 'em happy". I restapled most cable runs but
    probably missed a few areas --- given several thousand feet of romex
    used in the house.

    Part 2) Thermal/Acoustical Insulation Company comes along yesterday and
    sprays foam insulation which pushes some of the poorly stapled romex
    runs outside the stud bays, possibly allowing the romex insulation to
    be damaged when the excess extruded foam was "trimmed" back to the face
    of each stud bay by the foam installer. I asked the foam installer to
    let me know if he cut into any wires by mistake and he agreed to keep me
    posted, but using a continuity tester I later discovered a low voltage
    burglar alarm circuit that had been severed, pushed back into the wall
    and covered with extra foam. An accident? Perhaps, but it raises
    doubts. Severed wires on 24 gauge circuits are easy for me to detect,
    but nicked insulation on 12-2 romex is another story.

    Part 3) The foam insulation material (Icynene) began to shrink a
    half-day after installation, totally contrary to the manufacturer's and
    installer's sales claims, causing me to doubt the honesty and candor
    and/or knowledge of the insulation company. If they'll misrepresent the
    merits of their basic product, they probably won't be too forthcoming
    about collateral damage if/when they can cover it up and hide it from
    detection... figuring it won't be THEIR problem if someone gets
    electrocuted or the house burns down several years down the road.

    I can't think of any reliable way of determining if any of the romex was
    damaged without ripping out the foam and visually examining each of the
    wires and this will be difficult because the foam clings tenaciously to
    wiring insulation. I'm tempted to do this anyway because of the
    shrinkage problem but it would be nice to find a way of testing the
    insulation on each romex circuit without having to scrap away the foam.

    Any ideas?
  2. SQLit

    SQLit Guest

    You can test the insulation with an meggar. A unit that put out 500 to a
    1000 volts will work. Any scraped wire will be found quickly. Can not be
    powered up and can not be connected to anything. Recepts and switches ok,
    lamps no.

    I have a Speary that is ancient, AVO is another brand.
  3. Ben Miller

    Ben Miller Guest

    Think "Romex". A megger won't tell him anything. What are you going to meg
    it to? Ground? The insulation could be stripped from an area of the hot
    wire, but there would be no path for the megger current to flow through.

    Visual inspection is the only way to do it reliably.

    Ben Miller
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