Is such a tool available?


Old 06-16-05, 07:40 AM
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Is such a tool available?

I'd like to find out the distance of a couple of wires going from the main breaker panel to a certain appliance. Is there a tool available that can measure this via principles of resistance somehow?

I know, yes, I can easily break out a tape measure but the reason I ask is that the wire runs through certain parts of the attic I literally cannot get access to.
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Old 06-16-05, 08:15 AM
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You need a Time Domain Reflectometer. This is used to determine the length of wires by engineers. Maybe you can rent one somewhere.
Old 06-16-05, 12:14 PM
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or if you have a good friend in the telephone business... an outside cable maintenance guy would have a TDR that would measure it after you remove the power..
Old 06-16-05, 03:18 PM
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hmmm...ok I will bite.....Why do you need to know this??

Are you looking for the voltage drop in the feed?

Otherwise I would just do a rough math many feet up the wall, then so many feet to the appliance many feet down the wall...throw on a few feet for good measure and be close enough.

Before I would go looking for any specialized equipment it might be easier to answer if we knew the need for the accurate measurement...
Old 06-16-05, 08:51 PM
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TDR's use the speed of travel in a transmission line. Today's units are pretty sophisticated,and can be readjusted for different types of cables. The default setting is aroung 0.6 X speed of light. I am not sure if a simple cable like Romex can be tested but , maybe.....

A high end four wire resistance bridge can measure the resistance of a wire, but it would require extremely fine resolution to differentiate between say 50 and 75 feet of #12 copper.

All in all, couldn't you just use a tape measure.

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