Thanks for the reply.
The device in question is a very old skydigi box (Sky is a satellite TV service we have in the UK) and for some reason it had a squared figure of eight but I had been using a regular non polarised cord and after years of use a number of problems were beginning to show.
I have since took the skybox apart and followed where both pins go, and the circler pin went to an on-board fuse before anything else which I am assuming is the live and the squared one had one long track on the circuit board that looked like it was a common natural return for the various chokes and other components on the mains side of the board.
I also marked the cable with a red marker pen to show which side is live two after testing it with a continuity checker.
Thanks
