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Marina Upgrades Improve Safety

New marina shore power devices can reveal hidden problems on your boat.

Electric Current at Marina Illustration

This is representative of only one of many possible AC fault scenarios that can lead to ESD. | Illustration: Courtesy, David Rifkin 

Picture this: You pull into a slip at a newly renovated marina for the night and connect your shore power cord as always. This time, instead of your air conditioner springing to life, the ground-fault-protection device (GFPD) on the power pedestal trips. You reset it to no avail; every time you try to connect, it trips. The marina owner shrugs and tells you some boats have problems with the new style shore power circuit breakers. You spend the night reflecting on the notion that new and improved somehow now means hot and sweaty.

If you have not run into shore power connection problems in the past, it may only be a matter of time as marinas comply with more stringent wiring codes and install sensitive monitoring equipment intended to make marinas and boaters safer. But why are these changes needed?


The Challenge

Wiring, wandering electrons, and water do not work well together. Our vessels provide a moisture-rich environment that can lead to corroded electrical connections, component deterioration, and electrical leakage. In a saltwater environment, the challenges are even greater, as salt crystals attract and hold moisture, accelerating deterioration and providing potential current leakage paths to ground. This is why the boatbuilding safety standards organization, American Boat & Yacht Council (ABYC) has special wiring requirements and standards for boats, intended to reduce electrical leakage in marina environments to minimum levels (30 milliamps). The standards require an equipment leakage circuit interrupter (ELCI) for boats, which serve the same purpose as GFPDs for shore power pedestals. Think of it as double protection. Troubleshooting both devices is similar.

The Danger

Someone who enters the water in a marina is at risk for electric shock drowning (ESD). Electricity can leak into the water from the wiring of the dock or marina, or from boats connected to the marina or dock's power supply. A swimmer can be immobilized by even tiny amounts of alternating current flowing through the water, resulting in drowning deaths caused by paralyzing muscle contractions. The new dock electrical supply systems can detect electrical leakage at very low levels, preventing damage to vessels and reducing the risk of ESD deaths if anyone enters the water.

Safety Alert

It's very important to remember that 120-volt AC power can be lethal, and even more so around water. If you're not completely knowledgeable about and skilled at working on AC marine wiring we recommend you secure the services of a qualified marine electrician for help. 

The Safe Solution

Shore power installations that comply with the National Electrical Code (NEC) Section 555 wiring standards, established in 2011 and updated in 2014 and 2017, require the presence of current sensors on the hot and neutral wires that bring shore power to the service pedestal on the dock. These GFPDs are monitored by microprocessors that constantly compare the amount of current that flows through the hot and neutral wires to your boat (and all other boats connected to the same GFPD device). Any difference means the "missing" return current must be going to ground through the safety wire or through the water, raising the possibility of an electrocution drowning for any person who enters an alternating current (AC) electrical field in the water.

Someone who enters the water in a marina is at risk for electric shock drowning.

If there is a differential greater than allowed by the new standards (30 milliamps), the device trips and stops all power flow to your boat. Other GFPDs farther up on the dock feeder circuit trip at 100 mA. This means that if several boats have leakage even under the 30 mA limit at their dock pedestal, the accumulation may cause the dock feeder circuit to trip, cutting power to the entire dock. For our purposes, we're only going to talk about the GFPD on your dock pedestal.

AC Fault Indicator

Is It Safe?

If your vessel doesn't have a shore-power AC polarity/fault indicator, it's strongly advised to have an ABYC-compliant indicator installed. ABYC standards require either a visual or auditory warning indicating the presence of a faulty AC power connection. It's possible to check your shore power supply cord with a voltmeter, but this procedure exposes the tester to potentially lethal voltages on the probes of the meter. Inexpensive voltmeters may not have sufficient safeguards built in to be safely used on line voltages present on shore power cords. If you do not have the technical knowledge or professional-grade meter necessary to safely conduct this testing, seek the assistance of a qualified technician.

Basic Troubleshooting

Repeated tripping of the pedestal shore power GFPD indicates the presence of an electrical fault in the shore-power cord or on your boat's AC supply wiring.

The following steps can help in establishing a working connection. If not, they provide a foundation of information that you can use to take further steps in troubleshooting. The following steps address several basic causes of dockside GFPD tripping. Your vessel may have more than one factor or issue causing the breaker to trip, making troubleshooting more difficult. If your device trips on a seemingly random schedule, it's a possible indication of multiple faults. Perform this series of steps to try to isolate the source of the fault.

As you perform each step, watch closely to see if the shoreside GFPD trips. If possible during troubleshooting, ensure that your vessel is the only one on that shore power feeder circuit.

  • Turn off all alternating current (AC) powered circuits on your vessel including the shore power master switch or breaker isolating the shore power from your vessel's circuit breaker panel.
  • Unplug your shore power cord at both ends.
  • Reset the shore power GFPD if it was previously tripped. Typically, this will be a reset switch or button on the shore power breaker panel.
  • Plug your shore power cord into the pedestal on the dock. Be extra careful not to drop the other end of the cord into the water. (When connecting shore power for normal use, always connect the boat side first.) If the GFPD trips with only the shore power cord plugged into the pedestal, it indicates an electrical leakage or a short on your cord.
  • Plug the cord into your vessel.
  • Check to be certain that your boat's shore power polarity indicator (often installed next to the shore power circuit breaker or switch on your vessel) shows the shore power to be of the correct polarity. On my vessel there is an orange light to indicate the presence of power and a green light to indicate proper polarity. If your vessel's indication system is different, consult the manufacturer's manual to ensure correct interpretation.
  • If your vessel has a switch that selects between shore power and inverter power, select the "shore power only" position. Most modern marine inverters automatically do this, so you may not have a switch to isolate the inverter from the shore power system.
  • Turn on the shore power master switch on the boat's circuit breaker panel. Turn on one 120-volt powered system at a time from your boat's AC circuit breaker panel and any power switches on the equipment itself. If the shoreside system does not trip, turn that system off and go to the next system. Some 120-volt electric systems, such as the water heater or refrigerator, will not demonstrate a fault until the thermostat sends power to the appliance. You may need to run the hot water or turn down the refrigerator temperature until the unit cycles on. Air conditioners and refrigerators may also have a water pump that cycles on and off. Repeat this process until the system causing the dockside GFPD to trip is found. If nothing trips the GFPD, start adding systems one at a time until all systems are turned on. You may have several small leaks and the GFPD will not trip until all of the leaking systems add up to 30 mA.

How To Use A Multimeter

A Common Culprit

A commonly reported source of GFPD tripping is interconnection of the neutral and safety ground wire systems on a vessel. ABYC wiring standards prohibit the interconnection of any AC circuit neutral to the safety ground system anywhere on a vessel. There are exceptions for inside generators, inverters, and isolation transformers, which because they originate on the boat, normally won’t leak current into the water, but this is beyond the scope of this article.

Many vessels have been found to have the ground and AC neutral wires interconnected.

The only other place they're allowed to be connected is at the dockside power source box. Despite this, many vessels have been found to have the ground and AC neutral wires interconnected somewhere on board. Doing so can be very dangerous to persons on the vessel and those in the water nearby in the event of a fault, short, or electrical leakage. Some larger home appliances, such as 240v AC dryers or water heaters designed for home use, may have their neutral and safety wires connected internally to the chassis, which violates the ABYC requirement. Some galvanic isolators also send a test pulse, which may cause the GFPD to trip. If you have one, you can temporarily disconnect it by jumping the incoming and outgoing ground wires. Also, as mentioned above, new boats built to ABYC standards have an additional ELCI that does the same thing as a GFPD but is installed on the boat at the AC panel. It will also trip at 30 mA of leakage, and you may need to test this device in the same way. Because of small variations in sensitivity, the shore power pedestal GFPD may not trip at exactly the same time as the boat's ELCI.

What Do I Do If There's A Problem In A Specific System?

Turn off the system that is causing the leak, and don't power it up until the source of the leakage or the neutral/safety ground interconnect has been found and corrected.

Do I Try To Fix It Myself, Or Should I Get Help?

Boats often collect an assortment of modifications and additions to their electrical systems. Color coding of the wiring used in modifications to both the AC and direct current (DC) sides may no longer comply with industry standards intended to make clear the voltage levels present on each wire. Be VERY careful to determine if the circuit you're about to touch is high-voltage-alternating or low-voltage-direct current. The use of a voltmeter to confirm this is an essential safety procedure prior to touching any live circuit on a boat. This is another reason to have the boat AC side completely powered down when troubleshooting is started.

GFPD manufacturers indicate that in the absence of a genuine electrical fault or prohibited neutral to safety ground interconnect, the next most commonly found source for GFPD tripping problems stem from improper inverter installation. Modern inverters are complex and powerful devices; do not underestimate the knowledge required to troubleshoot these systems. Contact the manufacturer of the inverter or an appropriately certified marine technician for assistance in determining if the inverter may be causing the GFPD system to trip.

Basic troubleshooting for AC electrical system faults will involve inspecting all connections to ensure they are clean, corrosion-free, and dry. The hidden side of the shore power receptacle on the boat is a common location for connection deterioration (sometimes causing fires) and should be inspected for any indications of overheating or corroded terminals. The boat's AC wiring should be inspected visually and electrically (using a volt ohm meter) to ensure there is no unauthorized onboard interconnection between the AC neutral and the safety ground system. Further, it may require the use of a clamp-on ammeter and voltmeter to isolate the source of low-level electrical leakage on an individual circuit. You should attempt these procedures ONLY if you are familiar with the use of this test equipment and – most importantly – are aware of the dangers of working with AC circuits.

Isolation Transformer Solution

Finally, after ensuring that your boat does not have any active faults or wiring problems, there is one solution that will successfully address the following:

  • Stop current-induced onboard galvanic corrosion.
  • Eliminate concerns about reversed polarity from the shore AC supply.
  • Prevent current leakage on your vessel from entering the surrounding water and the ground wire system.

This all-encompassing solution is the installation of an onboard isolation transformer. These units are installed between your shore power feed and the onboard 120-volt circuit breaker panel and completely isolate the hot, neutral, and ground wires from the shore power alternating current system.

David Turley

David Turley is a commercial jet captain, a certified Airframe and Powerplant aviation mechanic, and a lifelong sailor. He is currently checking the AC wiring on his 44-foot Bruce Roberts ketch and sails on Delaware and Chesapeake bays.