With a pure 240 volt circuit, you have two hot wire leads (which create the 240 volts) and an equipment ground wire. There is no neutral wire as required in a 120 volt circuit.
A note about 4 wire 240 volt circuits:
Some plugs are designed to run an appliance on a split phase circuit and provide 120 volts and 240 volts at the outlet. They use 4 wires, black, red, white (neutral) and ground (green), with the black and red wires being "hot" in that case. The neutral wire is designed to carry an unbalanced load between the two phases of the circuit. The installation is similar to a three wire system, you just have another wire, a white neutral wire that connects to the neutral bar in the panel and the neutral terminal in the receptacle.