Quote Originally Posted by The Master View Post

The good news is that the circuit has now been running for over 7 hours and hasn't randomly triggered once. Maybe the interference is coming from something that's only on at night.
Your switch wiring is very close to resonance to communications r/f frequencies either private or GOV If you are running X # of meters you could be resonant at 1/4 wave or 1/2 wave . . . perfect as an antenna. As indicated above a load so as to define the actual switch event, an opto solution, or if you can determine the source even a choke to block r/f.