Lutron CB933 is a cable tester for tracking and identifying up to 16 cables.
Operation Description: Connect the ends of the transmitter cable (CH1 to CH16) to each wire of the track under test. Plug the "COM" end of the transmitter (black) into a known wire.
At the other end of the tested track, connect the "COM" (black) end of the receiver to the known wire. Connect the red tip of the receiver to the wires of the cable under test in turn - if the wire is not open the display shows the number of the wire (from 1 to 16) according to the transmitter tip connected to it.