Here are a couple of ways you can trace down existing electrical wiring circuits.

I like the ease of use and portability.It can be used in a light fixture that uses standard A-19 lamps,outlets and on exposed wires. Also you can use this style tester by yourself saving trips back and forth between the breaker panel and the area your working on. For more information visit the Sperry site. http://www.awsperry.com/catalog?item=cs-550a Next up is a tool I use for tracing known "dead circuits". PRO3000 Tone & Probe Kit

This can be used on phone,cable tv,and computer cabling as well.I like this one because I can find buried wires in walls,cabinets as well as the dreaded attic and crawl spaces.You have to remember that this tool is designed for tracing low voltage application but you can use it if your 110v circuits are dead.If you hook it up to 110v you'll blow up the transmitter. Other methods require a helper.You can use the old yell back and forth to each other or you can use 2-way radios .

These radios are great when working with 2 people that may be out of yelling range or in a quite setting like a doctors office where screaming out "is that it" is not practical. One more method you could use in two ways depending on you environment is to use a music radio plugged into the outlet you are working on. You could plug the radio in and turn up the volume,if conditions are right, or you could run an extension cord to get the radio closer to your panel when searching for the right breaker. Very rarely do I go on a service call and find a perfectly marked panel let alone enough information to shut off the correct circuit.Therefore we must use the proper method to find the breaker to work safely on the circuit.

Sparky