I am reinstalling a 230/115 volt 1/2 hp pool pump.

What is confusing me is this. The circuit breaker is a double 40amp. I have assumed this means that it is 220volt circuit. However the wiring is only a three wire romex cable in a conduit. The wires are black and white with bare copper ground.

Now in every post I see online they say for a 230volt setup you should have a black, red and green wire. I am totally confused. Was this originally wired incorrectly? The pump is the original ( about 25 years old ) and was installed by the pool people. The switch on the outside wall is also marked 115v. Inside the black clip is in the 115v position.
The wiring and the clip inside suggest it is set up for 115 volts. So why is there a double circuit breaker?

220 volt circuits are made up of two 110 volt legs. It appears that whoever wired this up used the neutral leg/white wire as the second 110volt leg. 220 volt circuits MUST BE GROUNDED. Your new pool pump must be set in the 220/230 volt mode. If you have an electrical tester, check the voltage between ground and the white wire and then ground and the black wire, you should get a reading of 110 volts in each case. In effect here, the ground wire is neutral and is highly important that this connects to the ground on the pump otherwise there is great danger of electrocution. Another way to visually confirm this a 220 volt circuit, is to pull the cover from the breaker panel and see that the white and black wires are connected to your 40amp 2 pole breaker. When making your connections to the pool pump, apply black or red tape to the white wire, this will correctly identify as a hot wire for future reference. As always, if in doubt, consult an electrician.

Yes I took off the breaker panel cover, and yes both black and white wires are attached. Since I need some other electrical work done anyway, I'm going to call an electrician. I don't really want to mess around with stuff I'm not sure about.

Thanks much!

You pretty hit the nail on the head. Couldn't have answered better myself