July/August 2018
When renovating houses as a hobby, I need to locate powerlines inside the walls and also underground. What curcuit can I build that would be useful? Also, what is the theory of how such a detector would work?
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If you can ensure that the power is OFF (e.g., the main fuse or circuit breaker is open) you could just connect a battery at the end of the power line to be traced, and use a buzzer or test lamp to discover the power line(s) that connect to it.
But... It’s so much simpler (and a lot safer) to just buy a wiring circuit tracer. The device consists of two parts — a radio-frequency (RF) generator that is clipped to one end of the wiring to be traced, and a second instrument that will sniff out the wiring that carries the RF test signal.
Check the Internet for recommendations and merchants.
The two main ways to trace wires is by inductive or capacitive pickup and by using a metal detector.
If the line is active and carries AC current, then an open inductor (coil of wire) connected to a simple audio amplifier and headphones or speaker will create an audible 50 or 60 Hz buzz near the current-carrying wires. A bulb with a blinker placed as a load on a circuit helps identify a particular line. There are also high-frequency modulated loads to help tracing, e.g. https://www.youtube.com/watch?v=GcaKaAISzjQ.
Capacitive sensors, e.g. https://www.amazon.com/Sperry-Instruments-VD6505-Non-Contact-Sensitivity/dp/B000GLAC5G/ref=sr_1_3, can detect energized lines with no current flowing, which may be useful to identify an unused line inside a wall.
Finally, metal detectors may help to trace wiring inside metallic conduit.
