First the language about the Ground Fault Protection of Equipment (GFPE) for the receptacle outlets which supply individual vessels is the permissive can rather than the regulatory shall. That being the case I would expect the marina owners and/or operators might take the least expensive compliant approach of installing the 100 milliamperes trip point GFPEs on the feeder and not install individual outlet GFPEs.

I can now understand the difficulties that would be encountered using a highly sensitive ammeter to measure any apparent current in a vessel's external power cord the test current supplied from the marina's electrical system. The vessel under test could have a modest amount of leakage and still put the total of leakage from that feeder over it's 100 milliamperes trip setting.

Let me ask for feedback on 3 possible methods of predictive testing of individual vessels for any ground faults on it's electrical system. First we need the answer to a critical question. Does the American Yacht Builders Association's standard E-11, AC & DC Electrical Systems on Boats require or even permit the connection to the Grounding Electrodes present on the vessel to continue to be connected to the Grounded Current Carrying Conductor while the vessel is receiving power from an external source? If it does not have previous versions of the standard required or allowed such connections?

What if at the first time each vessel requests marina power you open the breaker and plug the vessels shore line in. Without closing the outlets breaker you test the Grounding Impedance of the vessel's external power cord with a clamp on grounding impedance tester. Ideally the impedance will be so high that it would be beyond the ability of a Grounding Electrode Impedance Tester to measure. But if there is a ground fault, on the vessel, the impedance to ground of the vessel's unintentional Grounding Electrode would be measurable. OHMS law calculation should predict how much current would flow to the Unintentional Grounding Electrode on the vessel if the pedestal's outlet breaker were closed. The marina's operator could set an acceptable level of leakage which might well be none. Not allowing any leakage would prevent the leakage from all vessels supplied from a given feeder from adding up to the feeder's GFPE trip level. Exceeding the marina's maximum predicted current leakage would be a failure of the connection pretest and the marina operator would decline to provide marina power service.

Second possible predictive technique might be to measure the insulation integrity of the vessels electrical systems and its connected loads at the highest sensitivity on an Ohmmeter of adequate sensitivity prior to plugging in the vessels External Power Cord. If there is a Ground Fault in the vessels AC wiring system it should show up as a measurable resistance between the Equipment Grounding Conductor of the vessel's External Power Cord and the Current Carrying Conductors of the that Cord. A measurable resistance would be a failure of the connection pretest and the marina operator would decline to provide marina power service.

Third technique, admittedly at additional cost to the Marina's operators, would be to temporarily supply each newly connecting vessel through a portable Isolation Transformer, which need not be of sufficient capacity to supply the vessels full load, to check for an imbalance of current flow in the vessel's External Power Cord. Such an imbalance could only be caused by a Ground Fault on the vessel's AC wiring system. Once again a measurable current flow in the Vessel's External Power Cord would be a failure of the connection pretest and the marina operator would decline to provide marina power service.

As an aside a marina operator could choose to make an isolation transformer, of adequate size to supply a vessels load, available to vessels that have a Ground Fault on the vessel's electrical system. Such a transformer would create the equivalent of a Separately Derived System to supply power to the problem vessel.

Regardless of whether such an isolation transformer is offered they could offer contact information for every AYBA certified electrical technician doing business in the local area. I would imagine that it would be an hours work to rearrange the location of the main bonding jumper on the vessel's electrical system if that is the cause of the fault. In many cases that would only require relocating the main bonding jumper from the vessel's power distribution panel to the neutral terminal of the on board source of supply.

The technician could offer to install a transfer mechanism which would transfer the Grounded Current Conductor; neutral; in the same operation which transfers the Ungrounded Current Carrying Conductors from the on board power source to the external power cord. A common an inexpensive way to accomplish this, which is commonly used on recreational vehicles, is to use the external power cord as the transfer device. The on board power supply source is connected to a receptacle outlet that matches the external power supply cord. As long as the external power supply cord is the only source of supply to the remainder of the vessel's electrical system, unplugging it from the onboard source of supply powered receptacle would also disconnect all of the current carrying conductors. Plugging the cord into an external source of supply would connect all of the vessel's electrical system's current carrying conductors, beyond the onboard source of supply's receptacle outlet, to the external source of supply. If the fault was caused by an accidental connection to current carrying conductor in the branch circuits of the vessel's electrical system the same technician would be qualified and equipped to find the fault and clear it.

“ Tom Horne