Jeff,

I do electrical wiring as well as telephone and computer wiring. A few years ago, I was toning some NM cable (Romex if you know the brand) in an older building. I was using a Progressive Electronics 77HP tones to find which cable I was working with. I forgot that the toner was still on the cable when I energized the cable. As I was walking back to the place where I was testing the cables, I got this "sinking feeling" that I goofed. I climbed the ladder expecting to find a puddle of solder and a burned out toner only to discover the toner now had a green LED and was still functioning perfectly. So, to answer your question, some toners will work on "live" circuits, some will not.

I have a Fluke Intelliprobe Pro 200 that has indicator LEDs that flash when you are on a "live" data line. Testing a data line connected into a switch will yield a short indication on all pairs, but the Fluke will let me know if the cable is patched through and, with Arthur's excellent trouble shooting hint, that Fluke will tone across ground (you can use an AC outlet ground) and any pair connected to the switch and you will get tone. The thing eats 9V batteries, but it has saved me a tremendous amount of time testing network cables, so I look at the batteries as just the cost of doing business.

Rcaman

Americom, Inc.
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