New thermostat blows trip-switch when attached to chasis of dryer?

I got a new thermostat and fitted it. I first tried it without re-attaching it to the machine and I got the dryer producing heat, which indicates that this was the problem, but when I attach the new thermostat to the machine it trips my trip-switch. The new thermostat is not the same as the original one, but the guy in the electrical wholesalers said that it should be ok. Any ideas?