The code's ground fault trip threshold is 30 mA at the pedestal and 100mA cumulative farther up the dock feeder circuit. The real danger is that any AC circuit fault leakage currents through the water from a boat to ground, even tiny amounts, can drown a person not wearing a PFD who for what ever reason is in the water near the dock, a phenomenon known as "Electric Shock Drowning" (ESD) because AC current shock paralyzes muscles.Shore power installations that comply with National Electrical Code (NEC) Section 555 wiring standards established in 2011 and updated in 2014 and 2017, require the presence of of current sensors on the hot and neutral wires that bring shore power to the service pedestal on the dock.
Three years ago an upgrade project to install a larger holding tank on our Albin 25 meant relocating the batteries to make room for it. One thing led to another, including a costly upgrade of new wiring and revamping the antiquated 45 year old shore power setup. The existing shore power not only didn't have circuit breakers, but the only fault protection of any kind was an old fashioned screw in fuse on the hot side and no other type of GFCI protection and no way to tell if a reverse polarity situation existed. So in addition to replacing all the AC wiring and adding a galvanic isolator in the green safety ground wire circuit between the entrance outlet and a new breaker panel, I replaced all AC wiring with new marine grade boat cable and now I'm glad I did. So here's what the new breaker panel looks like, 30 amp dual main ELCI (Equipment Leakage Circuit Interupter) breaker (dual meaning ability to trip both hot & neutral sides) with reverse polarity indicator. I only have two circuits so far, one for the hard wired battery charger and another for a 15 amp accessory circuit with three regular plug in outlets (first outlet is GFCI). We don't have any appliances like air conditioning, 110V water heater, electric cook top or microwave, mainly use it for things like a fan, the Admiral's hair dryer, & curling iron when we're on shore power at a dock. But the panel does have expansion slots for three additional 15 amp ciruits.