The RV Electronics PLM-30A is a 30 amp voltage monitor and surge guard. It is suppossed to function much the way the Progressive Industries
EMS does. It is a surge protector and shuts off power from the generator or the pedestal if voltage goes outside safe range. RV Electronics is out of business, so if it doesn't work I'd remove it and replace with a PI EMS. Their lifetime repair or replace warranty can't be beat.
Surge Guard offers much the same protection, but only good for one year, no repairs possible.
Not sure how your unit should be wired, in a PI EMS 30 amp it is wired with Hot, Neutral, Ground (30 amp) in, and same 3 wires out. It can be wired between the shore cord and the transfer switch to only monitor shore power, or it can be wired into the output of the transfer switch to protect generator and shore power. If you don't have a transfer switch, it would be wired into the wires going into the breaker panel to monitor power from either the generator or shore cord.