An ample ground connection from the boat through the shore power cord to the dock all but eliminates the possibility of ESD cause by your boat. This simple test uses the boat’s 12-volt direct current power and a 50-watt DC light bulb to test the boat’s entire ground system all the way through the dockside end of the shore power cord.
Flip off both boat and shore main breakers, unplug the shore cord from the dock and bring the dockside end aboard, close to the boat’s DC circuit breaker panel. Use a 12-volt direct current light that draws at least a few amps (our 50-watt 12-volt DC drop light draws 4 amps).
Connect a wire from one terminal on the light to the shore cord’s ground (the outer metal housing on 50-amp 240-volt cords, as shown, or the bent prong on 30-amp 120-volt cords).
Connect a wire from the light’s other terminal to the boat’s 12-volt DC positive bus (shown clipped to the output of an unused 10-amp circuit breaker). If it lights, you’ve got a ground good enough to carry several amps, and also a proper connection between the boat’s DC negative and AC ground.
While you’re at it, connect the test wire to the shore cord neutral prong, too (the only unbent prong on 50-amp cords, or the smallest of the three prongs on 30-amp cords). If the light comes on, you’ve got an improperly connected neutral wire somewhere that should be corrected. This tests the entire ground system under your control — from shore cord end through the boat’s grounding system — even if the boat is fitted with a galvanic isolator or isolation transformer. Just be sure to test each cord and each shore power inlet receptacle.