When you drop a cable from an above location, you must locate the end of the cable at the desired lower location. If you are working alone and want to drop a cable a number of stories down a shaft or return duct in a house, it is difficult to locate the end of the cable.
Using a small piezo buzzer, you can locate the end of the cable even if you are working alone. The piezo buzzer (Radio Shack #273-074) generates 4.2 KHz of sound when a tone generator (or a 9-V battery) applies 3 to 16 V of direct current (DC) to it. Use an inductive amplifier with the buzzer and tone generator to intensify the sound if the walls have more girth.
- Buy a small piezo buzzer, which works on DC volts and is the diameter of a nickel.
- Enclose the piezo in a small weighted enclosure (like a small piece of pipe) so that you can drop the "drop cable" (which is just a cable with at least two conductors in it) straight down and protect the buzzer at the same time.
- Attach one end of the "drop cable" to the piezo buzzer's nodes, and then drop this end into the shaft.
- After lowering the "drop cable" down the shaft, connect the tone generator (or a 9-V battery) to your end of the cable. This will make the piezo "sound" at the bottom of the shaft.
- Go to the desired drop destination and listen for the sound. The wireless amplifier probe can detect the signal, but this is not necessary for most applications.
- Once the piezo is found, tie the cable(s) to be pulled up onto the end of the "drop cable" and pull them up.
This tip is helpful if you are fishing wires inside ducts that can't be easily seen from below. There may be many ducts, and all may be sealed. The piezo sound helps find the duct.
Randy Schwartz, owner of Handyman Plus (Blue Bell, PA), does commercial and residential telephone and cable TV wiring for the home or office.