[JRTJH]

Amperage is the "working load that produces heat" part of electrical items.

As voltage (the pressure in the hose) goes down, the current (volume in the hose) must go up to maintain the amount of "work" the appliance performs.

As an example:
1600 watts at 120 volts carries 13.3 amps through a circuit breaker
1600 watts at 104 volts carries 15.4 amps through that same breaker...

So, in this example, if you're plugged into a campground pedestal supplying 30 amps to your trailer and the voltage is 120 VAC, your air conditioner drawing 1600 watts will run "OK" with a 15 amp breaker but will "trip" the breaker if the voltage drops to 104 VAC.....

On the "other side of that equation", most air conditioners are wired to 20 amp breakers. So, it's going to be a "happy camper" buzzing along at 120 VAC while drawing 1600 watts. With that 20 amp breaker, if the voltage drops to, say 95 VAC because of heavy useage on the campground grid, that 20 amp breaker will not protect your air conditioner (designed for 13.3 amps of current) from receiving the increased current required to maintain 1600 watts to the compressor, which will be in the 16.8-17 amp range... That will produce increased heat in the compressor, probably damaging the internal components... It may "keep on running while almost smoking" that weekend. But sooner or later, the results of being overheated will take its toll and you'll be replacing the rooftop unit.

The 20 amp breaker won't "protect your air conditioner" from low voltage or high current.... That's why an EMS is so vitally important.