the grill or base element in top oven is going to earth, the best way to find it is, switch the electrics off to cooker, remove the two wires to the bottom elemet, tape up and switch the power back on try oven , if it does trip replace the wires and remove the wires making note where the colours go to the grill, when it stops tripping, that is the element, there is only 2 elements on top oven, cheers
peterb, February 2005