the size of the wire should not be a problem, i was doing my oven like that and the contactor stuck in the test runs and the circut board burned out but I was able to solder it back and am just using one element until I can get a pid and ssr, the wires never got hot, I think the biggest thing is if the contactor will take the amperage that both elements are drawing. It might stick or burn out. just do some test runs to see what happens and have a fire extenquisher ready
