Even if the device is not immediately affected, damage may have occurred which could cause the unit to malfunction and even fail at some point in the future. This is commonly known as electronic rust. A high voltage surge can cause the motor to suddenly stop working with no apparent outward cause. Low voltage will cause the motor to slowly burn up. You'll smell the burnt insulation and wiring.
Damaged equipment comes from two sources, external and internal.
Both can lead to damaged equipment if steps are not taken to prevent them.