Hmmm... It is a 32amp plug so it goes straight to the fuse box, although it has to travel quite a long way. Maybe that is the issue.
Well, the controller allows me to set a deg/hour rate, which I set according to a firing schedule I researched. So from that I can work out how long firing should take to reach a certain temperature. Assuming it actually heats up at that rate, which on the Bisque firing it did.
Is it normal for the temp rise to slow down as it gets hotter? Perhaps I am being naive to think it would rise at the rate set on the controller? In the end it was going for 18 hours and hit 1239deg and I switched it off as I didn't want to leave it overnight knowing it might not be functioning very well.
I don't mind if it takes a long time to reach temperature, but the fact the temperature keeps dropping then rising again suggests to me that it is not right.