Hmm, although our house is an older property, the previous owner was an electrician by trade and he wired in some external lights and an external power point. I wonder if he installed any fancy earthing for that external power point which feeds my observing hutch?
On a similar note, I once had a circulating current in my system that made the auto guider cable heat up. This was traced to a faulty mains adapter where a big metal heat sink had rotated inside the unit and was actually shorting to the metal case. As soon as this was repositioned correctly, the circulating current stopped.
This electrickery can be quite scary stuff!
Cheers
Dennis