Switching power source causes motor to stop 1

[surf40]

A friend of mine is an electrician that has never worked with motors before. He asked me to help him out. He has a customer that has a 120v 60 hz AC electric motor that has some medical applications. It’s power source is a wall socket. They are trying to connect it to an alternate power source (a generator). They have a switch that will change the power from the wall to the generator. The generator is providing the same 120v 60hz. But when they throw the switch to change the power source, the motor stops. During the switch change, the motor is without power for about 100-200 ms. He can disconnect the generator after the motor stops, and when he connects it back up, the motor will start and run just fine.
So what is he missing?
Thanks

Surf40

 

[OperaHouse]

There are UPS supplies where the inverter operates all the time. Line voltage powers the inverter. The output is never connected to the power line. Since the inverter is always running, there is no transition to worry about. e might want to consider this approach.