The 2011 National Electric Code (NEC) contains new requirements about ground fault protection for Marinas. The reason for this addition is that in recent decades we have seen an estimated 100 electrocution drowning deaths. These incidents typically occur when individuals are swimming in fresh water marinas that, for any number of reasons may have faulted distribution wiring, or faulted boats connected to said wiring. This sets up conditions for fault current to flow through the water. Since fresh water is only a marginal conductor, even small currents can result in large regional voltage gradients, paralyzing and consequently drowning a swimmer. People are often surprised to learn how low a voltage gradient threshold is necessary to cause paralysis when submerged in water. While I’ve not yet had the opportunity to investigate such an unfortunate incident from a forensic / electrical expert witness standpoint, I have heard protests arising from misunderstanding by contractors, owners, and code officials.
In one case, a contractor appealed for relief from the relevant electrical code section (2011 NEC 555.3). The contractor and related parties claimed that proper equipment was not available, the threshold 100mA current was too high to protect swimmers from electrocution, and that continuity of power would be unmanageable for the marina owner. An investigation revealed all of these claims to be false, and upon presentation of these facts to the state board of appeals, the variance was not granted.
Of particular importance is that people must remember there is not not a black and white threshold current above which electrocution is certain. First, the body of water and surrounding Earth is effectively a semi-conductor of enormous cross section, and therefore has expansive spacial current densities and expansive iso-potential lines to match. Any amount of ground fault current limiting will theoretically shrink, although maybe not eliminate, the “lethal zone” in the water. Second, GFCI equipment in the 5-6 mA range used at points of utilization has this setpoint because the fault current is likely to be highly localized, and it is a balance against continuity of power (nuisance trips) and user safety. The 100mA level prescribed by 555.3 is permitted at the feeder level. In the multi-user environment of a Marina, this allows for a greater amount of diffuse ground leakage current without nuisance trips. Yes, if a boat pulls in, rents a slip and trips the ground fault breaker immediately upon connection to shore power, it creates a “nuisance”, but let’s not forget it also prevents a potentially deadly condition. Having spent time on a US Navy nuclear submarine in ports around the world, I can say that even at high quality facilities, shore power interruptions are routine and expected. It’s just a part of life in the boat world. The reality is, the owner of the faulted boat needs to get the problem fixed. One could envision the enterprising marina owner partnering with a local contractor to offer pier-side “marine electrician services” to remedy such situations for the benefit of all parties.