This question is just for my general knowledge and not related to a problem. I've read here a lot about pumps and matching impellers to motors. A good match is most efficient, an under-sized impeller is okay but not ideal, an over-sized impeller is bad for the motor. So on a two speed pump why doesn't the motor have a problem when on slow and the impeller is over-sized for the motor hp? I assume it has to do with the different RPM's and maybe different windings but I'm not sure. Please educate me.