Broken alarm wire

hookMarch 8, 2011

I have an elderly (30+ years) wired alarm system. It developed an opening in a loop which I have located to within a few feet, it is between 2 windows right next to each other. I know it is a broken wire or a bad solder connection. (I replaced the switches.)

I have temporarily fixed it by running a jumper between the magnetic window switches, but I would like to find the exact location of the break before I start tearing the walls apart.

The switches are about 3 feet apart, and the tracer tells me the wire runs under the sills. The tracer does not locate the problem.

I can remove the molding directly under the sill, but I expect I will just see a 2x4. If I must cut the sheet rock, I would like to do as little damage as possible.

I have not tried to measure the capacitance of the wire from each side as it seems to me that the wire is too short for that.

Any thoughts will be much appreciated.


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I don't think it will be possible to pinpoint it if it's buried in the wall between the switches. When you replaced the switches, did you check the wires for continuity? It would be very strange for existing wiring to develop an open unless you put a nail through it or something like that recently.

If you are convinced the problem is the wires, can you just abandon the existing wires, remove the molding, and run new wires?

    Bookmark   March 8, 2011 at 4:53AM
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Install a new line between the switches.

It is not worth the effort to try and repair a bad line, especially a short one.

Alarm wiring is low power and does not have any significant rules about installation or protection.

Putting it behind quarter round and under baseboards is a common location.

    Bookmark   March 8, 2011 at 8:20AM
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wires don't normally fail on their own. But little furry critters love to chew on them, causing failures of their own.

    Bookmark   March 9, 2011 at 3:06AM
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Yes I did check continuity, and it does seem odd that it is a bad wire for no reason after all this time. My test leads easily reach both wire ends. It started out as an intermittent, and got much worse over a couple of weeks, driving me nuts. It would go from 0 Ohms to 30 meg. Ohms, and back, now it shows as open. But I have it cornered. My guess is a finishing nail just nicked it.
I think that you suggest a good plan, to just run a new wire under the molding. It may be hard to get the wires to the switches with out cutting some of the good wires with the drill though.

Thanks for the help

    Bookmark   March 9, 2011 at 3:04PM
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I removed the molding (actually it is more like baseboard upside down) from under the sill, and found a space of about �". Plenty of room to run a new wire.
Of course I would like to know what happened to the old connection, but that would involve cutting and repairing the sheetrock, and my curiosity is not that great.
Thanks for the help.

    Bookmark   March 24, 2011 at 2:29PM
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Glad to hear that it worked out fine.

    Bookmark   March 25, 2011 at 12:32PM
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