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The Electrical Dilemma On The Dock

How much electrical current leakage is acceptable before your onboard systems shut down or a lethal accident occurs? New regulations to detect this leakage may impact you.

Dock wiring diagram

Have you been cruising and been refused a transient slip because your boat was tested by the marina and determined to have "electrical leakage"?

Have you or your friends suddenly lost electrical power to a boat at the dock? Perhaps this occurred during the week when you weren't on board and it caused your batteries to go dead, the refrigerator to shut down, and the cold cuts and frozen bait to go bad in your absence. This is a widespread problem with a simple technical solution.

Some leakage of electrical current is normal. In fact, due to the design and nature of modern appliances using electronic control circuitry as a foundation for their operation, current leakage may be more common today than in the past. But reporting of in-water electric-shock deaths in freshwater environments all over North America during the past 15 years have increased concern, driving standards-writing bodies to develop requirements intended to mitigate any possibility of this occurring.

So, What's "Normal" Leakage?

In my 2007 book "Advanced Marine Electrics and Electronic Troubleshooting," I noted that the International Electrotechnical Commission (IEC) limits acceptable ground-fault leakage to 0.01 mA (milli amps) to 0.75 mA dependent upon the appliance category. More recently I've read that maximum leakage values for permanently connected IT equipment can be 3.5 mA or more in some cases. The use of electronic "filters" on equipment power supplies that use capacitors are the essential cause. Simply put, a modern boat with an all-electric galley and sophisticated AC and refrigeration systems is going to have multiple power supplies that can and will contribute to the overall on-board leakage current when the equipment is running.


Read "A Preventable Dockside Tragedy" to learn about electric shock drowning and what can be done to prevent it.

This explains why the 30 mA trip rate for whole-boat leakage protection came about versus the 5 mA (ground-fault circuit interrupter) rate for shock hazard protection.

Leakage current is cumulative in a grounding system, whether on board the boat or on the dock. The National Electric Code (NEC) requires 5 mA-rated GFCI devices for all 15- or 20 amp service receptacles on a dock. This will work just fine for a small center-console boat with no more than, say, a 120 volt battery charger as an appliance on board.

Handheld AC leak clamp

Handheld AC leakage clamp

All of this has prompted marina operators to comply with "No swimming from boats or off the dock" signage at their marinas. Plus, more and more operators are performing these leakage tests for their customers, and before any transient boat is allowed to plug into the marina's shore power system. Some of the tales I've heard about the test equipment used to perform these tests is concerning, however, such as large yellow boxes with multiple display screens and test probes dangling from them. Don't trust anyone using a box falling under that description for this testing. All that's needed is what's known as a handheld AC leakage clamp.

Different Parts Of The World, Different Solutions

The fundamental requirement that does the most to cure this problem has been in place since about 1957, developed in South Africa for the gold mining industry: the ground fault leakage interrupter. You've seen this device in your bathroom or kitchen. The plug assembly with the trip and reset button installed on the face is called a GFCI and is commonplace today. These devices are designed to trip at a maximum of 6 mA of ground fault leakage current and rated as 5 mA devices. They're only for plug-in receptacles supplying power to individual appliances, and provide shock hazard protection in case of a ground fault to the metal housing of say, a coffee maker. GFCI protection on boats is required for any electrical receptacle in a galley, head area, or outside on a weather deck.

These issues are not exclusive to North America. Realizing that some ground fault leakage is normal with certain appliances, marine entities in South Africa, Asia, and Europe created, and use to this day, a 30 mA device called a residual current device (RCD) used in dock pedestals and on boats. These became mandatory in Europe under the European Recreational Craft Directive in June 1998. Before that, they were widely used voluntarily. This 30 mA trip value (significant in a real-world situation) has long been considered a reasonable compromise between equipment leakage current in total from a boat, and personnel safety.

Leaked current goes directly into an electrical system's grounding wire, recognized in the U.S. as the green conductor in a typical 120 volt dock wiring circuit. If a boat is wired to ABYC electrical standards, as more than 90% of U.S.-built boats are, then some of this leakage current can actually leak into the water around the boat. This isn't a problem in saltwater as the water is electrically conductive enough for the current to get carried to earth ground rather efficiently. Freshwater, on the other hand, is not very conductive, and the leakage current will stratify near the surface, creating a real — and often deadly — hazard for swimmers. Note that many bodies of water that might be mistaken for saltwater can change the degree of salinity, for example, if a freshwater river runs into it. So never swim around marinas or boats actively using inverters or generators.

Dangerous Currents

1 milliamp (mA) of electrical current is equal to 1/1000 of an amp (A); 1 amp of electrical current entering the human body can be lethal. Medical journals describe the effects of electricity entering the human body in the following way, based on a 120 volt 60 Hz shore power system. (Effects vary depending on body mass, skin roughness, and overall physical condition.)

  • 1 mA — Barely perceptible
  • 16 mA — Maximum current an average man can grasp and "let go"
  • 20 mA — Paralysis of respiratory and limb muscles
  • 100 mA — Ventricular fibrillation threshold
  • 2 A — Cardiac standstill and internal organ damage

"Whole Boat" Protection

Ten years ago, here in America, ABYC mandated installation of what we refer to as an ELCI (Equipment Leakage Circuit Interrupter) device in the shore-power system on all new boats. These are rated at 30 mA, just like global RCD units. This whole system is designed to mitigate in-water shock issues. The problem is that tens of thousands of older boats registered in North America are not equipped with ELCI devices, so in-water shock hazards still exist.

The good news? Adding an ELCI device to an older boat is quite possible. They're typically combined with the main shore power circuit breaker in 30- or 50 amp configurations, with the 30 mA leakage current breaker integrated into the device. Companies like Blue Sea Systems offer detailed installation instructions for these devices, and this can be a good upgrade for any older boat. The cost is about $200 plus installation — typically a one- to two-hour project for a certified marine electrician. That said, if your marina has upgraded its dock wiring to comply with the newest version of the national electrical code, then each dock pedestal will be equipped with a 30 mA ground fault protection device, making an onboard ELCI redundant.

What Does The NEC Say?

The National Fire Protection Association (NFPA) writes the standards that make up the National Electrical Code (NEC), which covers electrical installations in buildings and marinas. Within those standards is a series that addresses marina wiring: Article 555. Regarding ground fault protection, it says: Receptacles providing shore power "installed in accordance with 555.33(A) shall have individual GFPE (ground fault protection equipment) set to open at currents not to exceed 30 milliamperes."

This finally emulates what the rest of the world has been doing for years! Translated into plain English, this means that the plug you use to bring shore power onto your boat is now required to have a 30 mA trip device in the event your boat exceeds that amount of leakage current. This threshold has worked quite well globally and will NOT be a problem if all is well on your boat. Over 30 mA is indicative of a serious fault and should be checked out by a certified marine electrician, not your cousin who does house wiring.

Although I've seen steps in the right direction within Article 555, the latest 2020 version of the NEC contains a troublesome flaw, posing a significant problem for conscientious marina operators attempting to comply with recognized industry standards. Article 555.35, Note 3, discusses branch circuits, the supply circuits to each dock finger pier. "Feeder and branch-circuit conductors that are installed on docking facilities shall be provided with GFPE set to open at currents not exceeding 100 milliamperes."

That 100 mA ground fault device will create a problem, in my view. If ground fault current is cumulative in a wiring system — as already stated, it is — and you have 10 or 20 cruising boats with all the bells and whistles in electrical gear installed, let's say each with 9- or 10 mA of inherent leakage current, you won't be tripping the 30 mA devices now required for each boat plugged in, but odds are good that the 100 mA device at the head of the dock is going to nuisance trip.

The net result? Warm beer, smelly bait, and spoiled cold cuts. My question to the NEC team is, if each boat is protected at 30 mA, do we also need a 100 mA device at the head of the dock? I don't think we do. It serves no useful purpose. Should there be a properly rated overcurrent circuit breaker on the dock in the event of a genuine electrical short circuit? Yes. A 100 mA GFPE device? No! (See "What You Can Do About It" below)

What You Can Do About It

The 30 mA receptacle requirement is new and technically quite welcome, and the 5 mA GFCI requirement that has always been in place for 15- to 20 amp receptacles is just fine. The 100 mA whole-dock requirement is a mistake. Get rid of that and you'll be back to fully charged batteries, cold beer, and sandwiches that won't put you in the hospital.

If this is something that you regularly encounter, you can make a difference. NFPA is a standards-writing body just like the American Boat and Yacht Council (ABYC). NFPA creates the NEC (National Electrical Code), which licensed electricians are obliged to follow.

When developing standards, part of the process requires a public comment period before publication. Comments need to be addressed by the standards-writing committee. It's clear to me that this particular NFPA group is not hearing from the same public I hear from — boaters and marina operators. The best advice I can give, besides what is needed to mitigate the problem, is to share this article with your marina operator. They need to contact NFPA directly and complain, and so should you. This might get attention so the NFPA will make the appropriate changes. Otherwise dock power lines will be tripping without regard to the cumulative effect.

Contact NFPA via email at or by mail at Secretary, Standards Council, NFPA, 1 Batterymarch Park, P.O. Box 9101, Quincy, MA 02269-9101.

New NEC Requirements That Make Sense

A new requirement in NEC Article 555 recommends that the marina operator have a leakage current measurement device on hand: "Where more than three receptacles supply shore power to boats, a leakage current measurement device shall be made available and be used to determine leakage current from each boat that will utilize shore power." This is a great idea. Just remember that all onboard electrical loads need to be up and running when these checks are performed. Some cycling loads like refrigeration and air conditioning systems may not show up at the moment of the test.

Lastly, this newest NEC recommends periodic checks for AC leakage current "to determine when an individual boat has defective wiring or other problems contributing to hazardous voltage and current."

The takeaways? 1. Check with your marina personnel about precautions they're taking to measure current leakage from boats at their docks. 2. If your boat is older than 10 years and not fitted with an ELCI in your shore-power system, always check in advance with marinas you plan to visit to make sure they'll let you dock; or have the device installed in advance. 3. Never swim in the water around docks, or around boats at the docks, especially in fresh- or brackish water.

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Ed Sherman

Contributor, BoatUS Magazine

Ed Sherman is an avid boater and the author of "The Twelve Volt Bible for Boats," "The Power Boater’s Guide to Electrical Systems," and "Advanced Marine Electrics and Electronics Troubleshooting." He's the former vice president and education director of ABYC.