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Critters got into wires, determine damage location
Posted 28 July 2019 - 12:52 PM
I have a wired ELK system and a few weeks ago the alarm company called me on a weird intrusion alarm. Inside doors triggered, which cannot be reached without triggering other sensors first.
Upon inspection, two door sensors are unresponsive. They exit the cabinet from the same hole and head on the same direction.
I had critters in my wiring before, in the crawlspace, but input stainless mesh around all those exposed wires.
I'm trying to avoid going on a wild goose chase, tearing into sheetrock everywhere. Is there a method of narrowing down, where the open circuit occurred? The first line is about 10ft long the other 20ft. I suspect the chewing happened in the same location...
Posted 28 July 2019 - 03:25 PM
High voltage insulation tester (Meggar) and a stethoscope.
The high voltage/low current source should cause arcing and the stethoscope should be able to locate it by sound through the drywall board.
Posted 28 July 2019 - 06:14 PM
I figured out a solution. I was able to pull out the wire from the alarm cabinet and just placed it on the wall to determine an approximate location, which placed it within two studs.
I was under the mistaken assumption that critters don't like wires and only chew them because they are in the way. Wrong! This particular critter seems to have chewed them just because, stopped digging through insulation right after it hit the wires.
Posted 29 July 2019 - 07:23 AM
Yes, you may have a critter rotting inside the wall.
We had some professionals come in a find a dead racoon inside a cinder block wall by the smell. One brick was hacked out and replaced. I don't know how they were that accurate but the smell stopped then.
In the electrical utility world causing a cable to arc with a high voltage allows locating accurately by sound on cables three feet under the ground.
As a side: we had a lineman find a street lighting cable fault (only 120vac) by the tingle in his balls, standing on the sidewalk. When they dug, it was accurate. It's not fun, tearing up people's lawns and sidewalks in a research fashion. LOL
Long cables are now done with echogram equipment. The reflected impedance change show up on a graph calibrated in distance units.
Insulation less than 80 years old should be fire retardant. An insulation tester doesn't cause much heat with it's microampere capacity.
Edited by LarrylLix, 29 July 2019 - 07:25 AM.
Posted 12 August 2019 - 11:00 AM
Echogram? Isn't that medical equipment?
I have always seen it referred to as TDR (Time domain reflectometer) but there may be other names for it. If you have or can borrow an oscilloscope and some sort of signal generator it's a good way to find breaks and shorts. I have done it several time to find breaks in such things as sprinkler cables. Although short distances can be hard due to the short time delays. They make expensive equipment calibrated in distance but with a scope you just need a bit more calculation to find the distance.
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