Friends of mine have a circuit where the RCD trips but only after prolonged rain. There are a number of garden and security lights on that circuit so I very much suspect there is a junction box where water gets into it.

There are two challenges:
- Find where the cables are buried.
- Find the 'wet' junction box.

I assume this is a problem which electricity distribution companies have to cope with more often and that there is a well know solution.

For 1: Find where the cable are buried.
I was thinking to put an RF signal on the cable and then use an antenna/coil to find where they are. (Of course first disconnect it from the mains)

For 2: - Find the 'wet' junction box.
I was thinking of borrowing a Time-domain reflectometer (Or set one up with a pulse generator and a scope). But I have no idea how accurate those are, especially with multiple junction boxes upstream.

I am hoping for somebody with practical experience or knowledge/tips how/if these methods would work?

I have a scope, pulse generators, multi meters, a spectrum analyzer and a small electronic lab available.

  • \$\begingroup\$ The TDRs used by telecoms and power people are pretty accurate (about a metre at most error) and fairly easily available. For a long distance, a simple pulse generator and scope will probably be accurate enough. You will need to find the velocity of the signal though. \$\endgroup\$ – Peter Smith Jan 14 '19 at 12:45
  • \$\begingroup\$ @ Peter Smith I like your approach. The cascaded junction boxes can be the calibration of distance, each box returning a tiny glitch to the sending end. \$\endgroup\$ – analogsystemsrf Jan 14 '19 at 14:24
  • \$\begingroup\$ Thank you both, I have only theoretical knowledge about signal reflections and this is useful. \$\endgroup\$ – Oldfart Jan 14 '19 at 14:42

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