I have two sump pumps both are120v powered. One is the primary pump and secondary. The secondary pump has the power to take over for the primary if it were to fail. The only problem I have is if I have a power outage I loose everything. What I would like to do is have a relay or such be able to switch between normal power and Ac battery back with inverter. Any ideas for type of relay or switch?

 

An ordinary dpdt 120v ac coil relay or contactor , with the coil across the mains input, and the motors on the relay wipers, to switch between supplies.