Well, this is where the voltage going into your coach from the power pedestal can dip very low (say, below 104 volts) or swing very high (133 volts or more) depending on the condition.
A low voltage condition can be very hard on appliances that need serious start-up current (like air conditioners) while a high-voltage condition can be just as hard on electronics (like your computer, microwave, electronics, and most everything else you plug in). To remedy this situation, Progressive Industries has designed some mighty impressive voltage monitoring devices that will only connect when the unit senses good power. Otherwise the contactor is open (where no power passes through). Our units also include a MOV "surge protector" which eliminates the quick "spikes" that a relay can't act quickly enough to disconnect. So if you don't want to live in fear of the volt you need the Progressive Industries EMS models will keep this from happening to you.