This is a rather convoluted and twisted discussion mixing AC wiring
protection with short circuits and leaking AC circuits both in the marina and adjacent boats. By mixing it all together you can get rather confused. They are really separate, but associated topics.
- - It is my understanding the "RCD" is merely Euro-speak for USA GFCI circuit breaker (Residual Current
Device). It detects the current entering the device as un-equal to the return current (neutral) and disconnects the circuit. Obviously electricity is "leaking" to somewhere else. It could be through a human with one hand on the appliance/power cable and one foot in a bucket of water
(so to speak). The result can vary from curled hair to worse. Or electricity could be leaking back into the earth ground wire (green) but not sufficient to trip the circuit breaker.
- - It is this stray leaking current in the earth ground (green wire) that is of special concern to boaters. Typically to save money
, the manufacturer connects the AC earth ground wire to the engine
which is in turn connected to the propeller
shaft and propeller
. Secondarily the "bonding system" of all other metal on the boat - stanchions, chain plates, metal through-hulls, etc. is also connected to the engine
, et. al.
- - This minute stray current leakage provides the necessary energy to start and accelerate electrolysis
in your propeller and other fittings exposed to sea water
(salt water) and they start to be eaten away or de-alloyed. Zincs go first, but soon after the propeller and bronze through hulls follow.
- - It is all too common in old and less maintained marinas
for the shore power
systems to have disconnected earth grounds or inadequate wiring
. Some of it fried and burnt by old cases of dead shorts - and the wires never repaired or replaced. So you end up with all the boats connected to shore power
being "earth-grounded" together. A neighbor boat with a "leaking AC" system will end up sending that electrical current to your boat and system.
- - 1. You have "earth ground" green wire to protect appliance dead shorts and enable the C/B to trip. 2. You have "earth ground" wire to protect humans from being a surrogate earth ground. And 3. you have "earth ground" isolation from faulty shore power to protect your boat's underwater metal from being electrically dissolved.
- - Others have spoken to the particular ways to accomplish protecting you and your boat.