Amongst Tempo/Progressive Electronics other Telco products is the widely used 77HP toner and 200EP Inductive Amplifier. Most likely you will recognize these. I have older versions of both, which at the time were yellow. The 77HP would be connected to a line with clip leads, and the line could be traced and identified using the 200EP.
I have used mine to trace telephone wiring through though switchboard wiring bundles, in and around the museum and in many other ways. Note also; the 200EP can also be used to trace AC lines, by listening for the 60 Hz. AC signal from the line (toner not needed). It will "see" the 60 cycle current through several inches of wall and give a good indication of where the line is. If disconnected at the panel, the toner could be clipped to the line, and the normal signal traced in the same manner. However, in this application, I have always found the 60 cycle in the line to be sufficient.
In older times, an AT-8629 Test Probe (banana probe) would be used for a tracer, with the tabs of the probe clipped to your butt set. (See bottom photo) This past weekend, I picked up another of the banana style probes in a turquoise colour.
The advantage of the 200EP is greater sensitivity and the speaker being part of the probe making a three handed operation into a single handed operation. With the 200EP you don''t have to worry about the clips constantly falling off and trying to balance the butt set at your ear - after all I only have two hands
. However, I just wanted to point out both will work.
I have used my toner many times tracing wiring inside the walls and equipment in the museum. I recommend the acquisition of a Toner/Inductive Amplifier to anyone who does a moderate amount of premise wiring, or who is attempting to trace wiring through devices such as a switchboard.
These are relatively trouble free devices, though mine is many years old, all it has required through the years is occasional replacement of 9 volt batteries. They can be quite expensive if bought new, but some real deals may be found on eBay for lightly used ones.
As with all alkaline battery powered equipment, batteries should be changed at least on a yearly basis to prevent the possibility of battery corrosion.
Now to round out my suite of cable testing equipment, someday I hope to add a portable TDR (Time Domain Reflectometer) unit to locate bad spots within wires. It would tell me exactly how far down a line a fault is located. However it is not likely I will find one which is affordable within this lifetime
One can always dream.