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repairing ceiling electric heat cable

davidpaul52 | Posted in Energy, Heating & Insulation on January 5, 2006 02:28am

I accidentally pierced an electric radiant heat cable in a ceiling. The cable is 22 guage copper with heavy, white insulation. I know residential electric well but have never had this problem before. Can some one help with proper splicing techniques?

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  1. DanH | Jan 05, 2006 02:38am | #1

    You need to figure out the brand of cable and contact the manufacturer.

    If ignorance is bliss why aren't more people

    happy?

    1. davidpaul52 | Jan 05, 2006 02:41am | #2

      Wish I could find the brand, no marking on the cable except red dots. Also this home was built in the early sixties.....

      1. DanH | Jan 05, 2006 02:42am | #3

        There must be a box somewhere where the cable terminates. There may be visible markings in there.
        If ignorance is bliss why aren't more people

        happy?

        1. davidpaul52 | Jan 05, 2006 02:48am | #4

          The cables terminate at a wall mounted thermostat made by federal pacific (FPE), bu the cables have no markings indicating that they may be FPE

  2. User avater
    maddog3 | Jan 05, 2006 02:58am | #5

    is this cable a single conductor ?

    1. davidpaul52 | Jan 05, 2006 05:11am | #6

      Just turned the computer on, Yes it is a single conductor, #22 solid copper.

      1. DanH | Jan 05, 2006 05:24am | #7

        I doubt that it's solid copper. Probably some other alloy.
        If ignorance is bliss why aren't more people

        happy?

        1. davidpaul52 | Jan 05, 2006 05:28am | #9

          The freshly stripped end looks like shiny copper, but with such a small diameter I can't tell if  maybe it's just copper clad.

      2. User avater
        maddog3 | Jan 05, 2006 05:48am | #10

        well then, usually heating cables consist of the wire, a semiconducting covering, and the insulation.
        ..If the semi-con is removed, then all you have is bare wire.... check the terminations inside the thermostat ,chances are this is what was done to terminate the cable there, if so you can splice the bare wire preferably by using uninsulated barrel lugs to repair the circuit .... without the semi-con the wire itself will not heat up...but use fiberglass sleeving to cover the bare wire . Tape the ends with 3M fiberglass tape...anything else will melt where the cable is in contact with the ends of the sleeve.Heat trace cables use two wires separated by the semiconductor, and the terminations are made using a similar procedure.,but will use a special assembly from the mfr.this is a generic response, but the cable has to be repaired, and this is all I can think of

    2. davidpaul52 | Jan 05, 2006 05:26am | #8

      Here's some more info that might help. It's a deicated 240v circuit, 15 AMP. The thermo is wired just like it would be for elec. baseboard.  I guess the main info I'm looking for is what type of wire can I use? Will #12 solid cooper be acceptable or is there special wire (like more heat resistant) for this application. To be code approved does this splice need to be in an accesible box like any other splice or is ther a code approved method that can be re-buried in the plaster? If I have to, I can put a box in the ceiling, but prefer not to.

      1. User avater
        maddog3 | Jan 05, 2006 06:02am | #11

        you can use the same gauge, just make the spilces as solid and tight as you can...if you use wirenuts they will become brittle in time and fail

        1. DanH | Jan 05, 2006 02:27pm | #12

          Problem is, since this is heater cable thermal cycling will defeat just about any connection scheme you come up with.

          If ignorance is bliss why aren't more people

          happy?

          1. User avater
            maddog3 | Jan 05, 2006 03:19pm | #13

            well , that would affect the terminatons in the stat as well,
            .
            .. where that wire terminates, the connections are no different than ordinary building wire.....heat trace.....looks like 300 ohm antenna wire once the outer jacket and ground braid are opened.
            The terms are made by separating the two leads, skinning the ends, sliding heat shrink over the bare wire and braided ground, and sticking the whole thing into a transition that supplies power... once the semi-con in removed there is no heat buildup between the two wires ....... and his single wire is probably similarbut your point is well taken, that is why the splice must be crimped

            Edited 1/5/2006 9:19 am by maddog3

          2. DanH | Jan 05, 2006 06:15pm | #14

            There's a heck of a lot of difference between two-wire heater cable and single-wire cable. With the single-wire cable, the wire is what supplies the resistance, vs the semiconductor glop between the two wires in the two-wire case. So the wire itself gets hot.
            If ignorance is bliss why aren't more people

            happy?

          3. User avater
            maddog3 | Jan 05, 2006 10:17pm | #15

            ....then how would it terminate at the thermostat ? is it constant wattage?
            ..I'm asking, cuz I don't recall ever working with the stuff !.miles of heat trace though

          4. DanH | Jan 05, 2006 11:01pm | #16

            The cable would have to be of a fixed length, more or less. Any longer and current/wattage drops, any shorter and current/wattage goes up, threatening to overheat things.In fact, I'd expect the cable to be supplied in a fixed length, with the ends factory-terminated to ordinary wires.

            If ignorance is bliss why aren't more people

            happy?

          5. davidpaul52 | Jan 06, 2006 02:02am | #17

            Thanks to Maddog3 and DanH...., Some additional info, FYI... I did attatch a temporary jumper for testing purposes, and the heat seemed to work just fine. Also the gap I have to bridge in the wire is less than 1/4 inch. (a 3/16 threaded fastener pierced the wire.) The insulation around the conductor is roughly the same size as #12 NMB wire (not 12/2wg but a single conductor pulled from  the yellow12/2 jacket)

  3. bigman | Jan 06, 2006 02:24am | #18

    Hello, I used to do a lot of ceiling radiant cable, before Thermo-Ray came out with the heat wires imbedded in 12" wide sheetrock panels, and even that is now a dinosaur.

    For those that have never seen it, a heat loss for the room is determined, then you order the length/wattage of cable you need. There was a spacing formula we used depending upon ceiling size and openings such as recess lights.

    We used roofing nails, half driven into the plaster board, spaced according to wire wattage/length (it could be 2" - 6"). Then the heat cable was laced across the room fron nail to nail, the heat conductor was the stapled every 6" to the plaster board and the nails where removed. It was then plastered over. We tested continuity 4 times to make sure nobody F$#@ed the wire up.

    The spacing was critical because the ends of the run had 6' long thick insulation leads that were meant to be run down the wall to the Tstat, therefore you had to end up with equal ends (wher you started, was where you ended, think about it, what a PIA, got paid top dollar ).

    When we had an "open circuit" which happens, plant hangers, settling, etc, we would use a fine point set of test leads and poke a lot tiny holes to locate the open part.

    We would then use an asbestos coverd wired (same wired used under electric cooktops), solder a splice piece in and plaster over the splice.

    T. G. nobody asks for that type of heat anymore ;-)

    1. davidpaul52 | Jan 06, 2006 02:37am | #19

      Thank you Bigman, this may be the way to go (cooktop wire) What should I use to protect the bare conductor after soldering? Will heat shrink tubing stand up to those temps? Or should i use the fiberglass tape mentioned in an earlier post?

      1. bigman | Jan 06, 2006 02:57am | #20

        The splices where only a 1/4" long, we dug out the plasterboard a little and replastered right over the splice. Let dry for a couple days before you use the heat.

        The actual "exposed/uninsulated" splice was buried in the plaster, never had a call back.

  4. bar2750 | Feb 10, 2020 12:18pm | #21

    That heating Cable is mostly in 30 years plus buildings (Chicago downtown) you can just splice it to reconnect the circuit with butt connectors either red butt connectors or plain butt connectors with heat shrink.... and you’ll be fine.

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