Some submersible pumps have a gray motor box to start the pump & some submersible pumps have the new style motor box built in and is not lighting proof. some 240vac are two wire and three! I would like to know the difference between the 240vac two or three wired pumps because of the yellow wire for the third is either common or ground of what>?

The difference in the two pumps is that with a three wire pump the start and run capacitors are in the gray box. With a two wire pump the caps. are built into the motor. Because of this with a two wire pump you only need to run the 240v down the well to the pump. The yellow wire on the three wire pumps is the igh voltage wire that come from the start cap. I have used both pums but usually use the two wire because they are easier to hookup and the wire is cheaper because you only need to run three wires. (2 hots and ground) On large HP pumps you will always have three wire motors because the caps. get too big to get them in the motor. It is best to go three phase with big pump if you can.