When we lived in NJ the public power often went to about 103-104 volts in the summer on super hot days, and we never had a problem with our AC or any other appliance. We have two different energy management systems, both of them cut out about 103-104 volts, so I think that is a safe minimum. As others have said though, I truly believe the cost of the energy management "device" on my power line is worth way more than paid for it.
Ed Headington