How do you connect 240V electric water heater?

On a 120/240 volt distribution system the ground wire is terminated at the point where the service neutral terminated in the distribution panel. It is usually a double lug the neutral wire connecting into one hole and the ground wire connecting into the other hole. Through this lug assembly there is a machine screw that is inserted through the lug assembly and it screws into the metallic enclosure of the distribution panel. This action bonds the metal enclosure, neutral wire and ground wire bringing the point to a common potential of zero.