The best thing to do when you are going to wire a 220 switch is to make sure you hook up the ground and the hot so they are not crossed. If they are you are going to fry the appliance you are hooking up to the 220 switch and you won't want to do that.
220 volt lines are actually two 110volt lines out of phase meaning both wires are hot. You need to find a double pole disconnect switch with the correct amperage rating. the two white wires go one one side and the two black wires go on the other. The switch essentially cuts the wires apart.