Got called to a work shop today as UKPN discovered that they were getting back feed voltage down two phases. What I found out was when I pulled one of the cutouts then switched a 3 phase machine isolator on, (bearing in mind the the supply was only getting as far as the incoming side of the starter and not the motor) I was getting a reading of around 100V backfeed to the load side of the cutout. Stumped?