I would like to convert the wiring of my sprinkler system pump form 220 service to 110. The pump comes with an optional switch. The 220 line is controlled by a switch inside the house and line going outside to a box that the pump plugs into.

You need to remove 2 pole breaker and replace with single pole 20 Amp, if #12 wire.
One of the wires needs to be reidentified with white tape,(All junctions, at switch, and pump). Be sure pump is not too large for wiring.
Many pumps can be jumpered different so it may work on 240 volts. More efficient, less voltage drop, less work involved and cheaper.

Stratmanco... a sidebar question on the wire identification... is tape an acceptable means for identifing, or does it need to be painted? I've heard that tape is not allowed per NEC... yet I haven't seen any documentation to support that.

Thanks

I have never seen it in the NEC , BUT in this area it states in the local code that it is to be idenified by colar of tape- which would in this case be WHITE< VERY good answer STRATMANDO ::: Youal have a nice day and GOD BLESS ;;; F.B.E.

Thanks Eagle... I tend to think that is correct, and I've been doing it that way. I will continue to do so until someone proves it's not acceptable.

Thanks again.

The NEC uses the term "effective means" when talking about identifying wires. They left it up to the AHJ in other words. For info on when you can and cannot reidentify a conductor as grounded refer to 200.6, it is more strict than one might think.