What is the line-to-line voltage?

80 volts, but to what? Are you using a real grounding conductor for this measurement?

What are you using to make the measurement?

Digital meters have very high input impedance, and can indicate 80 V from an open conductor that runs in a cable by coupling from another conductor in the cable.

Occasionally I come across what may be this same problem. Check the voltage coming off the breaker. Check each line to ground and then to each other. It may be a bad breaker.

Hope this helps.

Sorry,
You will have to either turn the other breaker off while checking each line to ground, or undo the the termination points of the wire at the pump. What can happen is the voltage from one leg will go through the pump and return on the other leg with a drop, if the other leg is not getting voltage.