A while back I was involved in a discussion of shore line electric power that supplies wiring built in to boats. Further discussion has indicated to me that the problem that the marinas are having is corrosion that is caused by the split return path the neutral current takes when the neutral of the boats system is bonded to the engine or to the hull grounding plate. In a couple of cases I have observed in the time since the earlier discussion the zinks seemed to be boiling off the hull. The production of bubbles ceased instantly when I unplugged the shore line. The only remedy I have developed so far was to use a short pigtail with a male cord cap to connect the on board wiring to the on board power source and use that same short pigtail to connect the on board wiring to the shore line extension cord. This leaves the on board wiring's Equipment Grounding Conductor (EGC) not bonded to the boats ground when on shore power. This generates a couple of questions in my mind that I would like comments on.
Since the US NEC stops at the dock receptacle I believe that this technique cannot be an NEC violation. Would you agree?
Do you see any real safety issues with not having the EGC bonded to the metal objects, such as the engine, on the boat?
How could we guard against a fault in the cord, such as from chafing, energizing the lifelines or metal railings on the boat.
A Ground Fault Circuit Interrupter (GFCI) might prevent a tragedy but it would not prevent the problem from occurring in the first place. The universal installation of multi pole transfer switches that would switch the neutral with the ungrounded conductors across an entire marina would break the circuit without opening the EGC but every boat would have to have a switched grounded current carrying conductor for that to work.
Could we equip the boat with an isolation transformer that would break the neutral current return path that is going through the boat. The transformer would be in one of those plastic battery trays to keep it aloof from the boats grounding electrode system. The neutral of the transformer secondary windings would be bonded at the boats distribution panel rather than at the transformer.
I have never seen any complete answer to the marina stray voltage problem and I'm looking for ideas.
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Tom Horne
