It is possible to accurately determine if there are damaging or dangerous leakage currents in a moorage. It does take proper equipment
The list includes the following items:
1. An amp clamp meter capable of reading in the milliamp range. A Fluke 360 will cost about $600.
2. Some 30 amp and 50 amp connectors to make "break-out" adapters to speed up checking shore power
connections, as applicable.
The amp clamp must be placed over the power and neutral wires bundled together with the green ground wire excluded. The "break-out" adapters enable doing this without disturbing the shore power cables
which have the power, neutral, and ground wires bundled inside the cable jacket.
Amp clamp readings should be less than 2 milliamps for each boat's shore power connection. It may not be zero because there are some electronic devices, such as polarity error indicators, that apply very small currents to ground.
What you need to find are boats with shore power connections where ground faults exist. Worn or defective insulation
can result in modest leakage current
leakage in the 10 to 100 milliamp range, and wiring
errors (where the ground and neutrals are reversed) can result in leakage currents above 1000 milliamps. Such currents can be lethal to anyone in the water
I have used such equipment, and have found boats with leakage up to 3500 milliamps.