Reverse polarity?

[Trey5684]

Could someone explain reverse polarity, is it caused by an external problem from shore power pedestal, cord, plug etc. or can it be an internal problem in the boat? Shore power works ok for a while and the reverse polarity lights come on and trips shore power off. When this happens the volt meters drop from approx 115v to various voltages from 25v to 95v, confusing. Only items powered on the boat when this happens is the battery charger and refrigerator, when power trips the refrigerator switches to DC power and of course drains batteries. Boat has two shore power connectors but I believe one is basically just for a/c but a/c not running when this happens so boat is not drawing a lot of electric.
I already checked cable ends and plugs for corrosion and none found.
Thanks for any help

[jparsons121]

Those reverse polarity indicators are there to show when there’s voltage carried on the neutral and ground when it shouldn’t be. Given the additional symptoms with the voltage varying, Id inspect carefully your shore power cable. A broken wire or a bad connection could explain the voltage drop. Possibly because you’re carrying current on neutral and ground.