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When power at the dock lets you down
6/1/2020

Several months ago we heard about boat owners complaining of electrical problems at some marinas on the west coast of Florida. Leakage of electrical current at shoreside facilities is nothing new—and it can be deadly in some instances. Updated rules governing electrical installations at marinas were put in place years ago but apparently they didn’t solve the problem. We asked electrical expert Ed Sherman to explain what was going on. The following report is excerpted from an article he wrote for Marine Electronics Journal.


By Ed Sherman

So, your customer is ecstatic over their new boat and the $40,000 worth of electronic equipment you just installed. That is, all except for one minor detail that seems unexplainable: every time the boat plugs into shore power the main ground fault protection device at their newly rewired marina trips, shutting off the power to their boat and all their neighbors on the dock. What could possibly be wrong? After all they just spent $600,000 on their new dream cruiser. Further complicating the issue is that your customer says that when they took their first cruise down the bay and plugged in at a transient dock at a quaint and much older marina down the bay, there were no problems with the shore power. What’s up here?

To answer this question requires a look back at some interesting history relative to both dock wiring as well as boat wiring. Let me begin by identifying the root cause of the dilemma that has emerged. In-water electric shock death, more commonly known today in the marina world as ESD, is what got this ball rolling. Believe me, this ball has been winding down a long and winding road over the last decade, in part due to a general lack of understanding of the problem and its causes as well as changes in the choice of equipment used on new boats.

ELCI—a long and winding road

The ELCI, or equipment leakage circuit interrupter, was first introduced to the recreational boating world by the ABYC in July 2011. The winding road began there with general non-acceptance. Problems were plentiful; nuisance tripping was so prevalent that the ABYC extended its compliance requirements until 2012. This troubled me because I knew that similar devices, known as RCD’s, or residual current devices, had been in use for several decades in other parts of the world without incident. In any event, after altering design parameters and adjusting the ABYC E-11 standard to accept the European RCDs that were in use on imported boats without the nuisance trip problems ELCIs became accepted. These devices are now a requirement on new boats as a part of the National Marine Manufacturers Association’s (NMMA) boat and yacht certification program, which uses ABYC standards as its basis.

So, what do these devices do anyhow? They sense any current differential between the shore power hot and neutral conductors supplying the boat. Any differential indicates a ground fault, and historically these could exist for years without anyone knowing the difference. These leaks are simply too small to trip any conventional circuit breaker as used in shore power or onboard AC systems. The ABYC mirrored current ratings as used globally, 30mA. The intent here was to establish a reasonable trip point that could save lives but accommodate low levels of inherent AC ground fault leakage.

You see, on an ABYC-compliant electrical system the grounding system is connected to the boat’s bonding system, which means metal through-hull fixtures connected to this bonding system could act as a source for AC leakage into the water. The premise here is that if the boat is plugged into shore power and the dock wiring and fixtures have been tested annually (as required under NFPA—National Fire Protection Assoc.— regulations), then any fault or leakage currents will follow the low-resistance pathway back to the power source via the dock’s grounding system vs. through the water, helping to eliminate ESD.

Understand that all of this was counter to what the ABYC felt was a better solution, and that is to control this problem at the power pedestal supplying the boat. Back in 2009 when we at ABYC first started looking at all of this the dock folks simply did not want to discuss any of this, which is what drove the ABYC to act in ultimately mandating the ELCI. The issue with NFPA was the 30mA trip point and inferring personnel protection. As far as NFPA (which publishes the NEC—National Electrical Code) was concerned, 5mA was the appropriate level for protecting people and 30mA or more was to protect equipment only. We at ABYC knew from considerable experience that whole-boat 5mA (GFCI) trip rates were going to cause nuisance tripping on a wholesale level! Suffice it to say that the wording found in ABYC’s E-11 standard addressing ELCI devices is carefully crafted to not even discuss personnel protection. The definition found within E-11 is telling:  

"Equipment Leakage Circuit Interrupter (ELCI)—a residual current device (RCD) which detects equipment ground fault leakage current and disconnects all current carrying conductors from the supply source at a preset trip threshold.”

Let’s just say that the now known fact that turning off this leakage current has a fortunate side effect: it helps to eliminate AC current into the water surrounding a boat plugged into shore power at a dock.

National Electrical Code

ESD has certainly gotten a lot of press over the last 10-plus years, and in 2011 the National Electrical Code altered its standard for dock wiring to include "whole dock” protection at no greater than 100mA. This requirement carried over in the 2014 revision of NEC 70. Several of my marina manager friends attempted to do the right thing as they upgraded their docks, comply with existing NEC/NFPA requirements. The end result? Disaster. More wholesale nuisance tripping.

You see, AC current leakage is normal at extremely low levels. The important thing to remember here is that this leakage current entering the dock’s grounding system is both normal and cumulative. With 10 or 20 medium- to large-sized cruising vessels plugged in at a dock with a 100mA GFP (Ground Fault Protection) device at the head of the dock, nuisance tripping is all but guaranteed. It’s extremely important to note here that there may be absolutely nothing wrong with the boats in question, but rather the trip point for the dock’s GFP device at 100mA.

For marina operators that waited until the 2017 edition of the NEC to provide guidance, the problems got even worse.

Next week: Notorious leaky devices and testing for ground fault leakage current.


About the author

Ed Sherman is the former longtime education director for the American Boat & Yacht Council and the author of several books on outboard motors, onboard electronics and electrical equipment. He writes a regular column on technical electrical topics for Marine Electronics Journal.

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