4 wire = 2 hots, 1 neutral, 1 ground
3 wire = 2 hots, 1 ground.
4 wire allows you to split the 240 circuit in to 120 volts if needed, no neutral means no 120 volts, but you can still wire in 240 v plugs.
Ok don't need the 120's at all so I will just leave the neutral one unwired and just wire the three wires I have as you say.
Thanks a lot this saves a lot of trouble.