GFCI and ELCI breakers can be confounding, but heed their warning

6 Aug

I recently met cruisers who have been having trouble connecting their mid-80s boat to shore power pedestals equipped with GFCI (ground fault current interrupters) or ELCI (electric leakage current interrupters). Many months of working with electricians allowed them to plug into GFCI breakers without tripping them but still not ELCIs. So, what’s the problem, why did it take months to get it fixed, and what serious safety issues were uncovered? Read on…

In 2011 the National Fire Protection Association changed the national electric code (NEC) to require marina shore power systems be equipped with ground fault protection (GFP). These code requirements only impact new builds or significant renovation of existing marinas. It took states until 2014 to adopt these changes so it’s only been in the last five years or less that boaters have begun encountering marinas equipped with these technologies. Troubles reported from these early encounters led to a revision to the NEC in 2017.

The most recent versions of both the national electric code and American Boat and Yacht Council (ABYC) standards call for an ELCI breaker at both the pedestal and onboard the boat. These standards are only relevant for newly built boats and marinas so it will be many years before the majority of marinas and boats are so equipped.

A serious note

I started off writing this article about the pain boaters suffer dealing with these new marina shore power systems and how to deal with the issues. But the more I was reminded of the basic physics of electricity, the stronger I felt that these systems exist for our safety. I think we all as boaters — I certainly know I am guilty — can become lax about the potentially volatile relationship between electricity and water. Electro-shock drowning is a real and very scary thing. I’ll attempt to stay off the soapbox but please remember that the prohibition on swimming in marinas isn’t because the world is full of fuddy-duddies; it’s because it can be quite dangerous.

The basics

(Image courtesy BlueSea Systems)

Each alternating current (AC) circuit contains a hot, a neutral, and a grounding wire. The hot carries the electricity to the circuit while the neutral is the return path. Grounding conductors are a safety measure in the event of a fault in the circuit. They provide a safe path for the current to return in the event of a neutral fault and also a means to trip a circuit breaker if the hot conductor becomes exposed.

Though there are many similarities to how a boat and house should be wired there are some very important differences. One of the biggest is that each boat connected to a marina’s shore power system is essentially a sub-panel on the marina’s electrical system. This is an important distinction because a main service panel connected to utility power typically has a neutral to ground bond (the neutral and ground wires are connected in the electrical panel). But, there should only be one such bond in the system so any sub-panels wouldn’t have this bond. This difference becomes a complication when we disconnect from shorepower and start generating our own electricity with either a generator or an inverter.


Most people will be familiar with a ground fault circuit interrupter (GFCI) from household wiring where they’ve been required near water sources for more than 20 years. These breakers look for current flowing on the grounding conductor of the circuit and trip if current exceeds a threshold — that threshold is set at 5 milliamps for single circuit 15-20 amp household GFCIs and 30 milliamps for shore power circuits. GFCIs are available both built into outlets (above left) and in circuit breakers (above right) in nearly all amp ratings.

A GFCI trips when there’s current on the ground of a circuit. You may wonder why this is important and if you should really care. The short answer is yes.

A boat with a properly functioning electrical system but a failed connection in an appliance (image courtesy Boat U.S.)

Think of a metal-cased microwave on your boat. Imagine the clip that holds the cord where it enters the case breaks and the sharp metal edge of the case saws away at the cord as your boat is underway. Eventually, that sawing action results in a cut to the hot or neutral wire’s insulation. Now, one conductor is touching the case of the microwave. Fortunately, the case is grounded. So, if the cut occurs to the neutral wire’s insulation the result will be that return current is flowing on our grounding conductor. If the microwave is plugged into a GFCI outlet the outlet will see current on ground in excess of 5 milliamps and trip the protection in the outlet. If the hot wire’s insulation is cut a short circuit is created and trips the circuit breaker.


An equipment leakage current interrupter (ELCI) device makes sure that all electricity sent from a shore power pedestal returns. More specifically, the breaker detects any current that is leaking into the water. It does this by looking for an imbalance in the amount of current traveling on the hot and neutral wires. If less current comes back on the neutral than left via the hot it has to be leaking somewhere. So, the ELCI determines this is an unsafe condition and trips the circuit protection device.

A properly functioning circuit with a current coil measuring the hot and neutral (Image courtesy BlueSea Systems)

Why is this unsafe? Because even in a properly grounded boat some current will leak to the water via the tie between the AC grounding system and the boat’s bonding system. This current in the water is very dangerous to anyone swimming around the boat and also will cause accelerated corrosion of submerged metal.

In this diagram 30 milliamps of current not returning on the neutral (because it’s leaking to ground), causing the ELCI to open (Image courtesy BlueSea Systems)

The primary difference between an ELCI and a GFCI is the measurement used to determine if a circuit should be interrupted. A GFCI monitors the amount of current flowing through the grounding conductor and interrupts the circuit if a threshold — typically 4-6 milliamps for an individual circuit and 30 milliamps for a shore power connection — is exceeded. An ELCI monitors the current imbalance between the hot and neutral and interrupts the circuit if the threshold — typically 30 milliamps — is exceeded. GFCIs can be used on an entire shore power feed and on individual circuits but ELCIs are typically employed only for shore power feeds.

Both devices will successfully interrupt a circuit if there is current leaking back to the grounding conductor of the shore power circuit. But, if current is instead leaking through the boat’s bonding system and into the water the GFCI won’t trip because it’s not seeing any current on the ground conductor it monitors. On the other hand, the ELCI will trip because it sees a current imbalance between the hot and neutral — more current going out on the hot than returns on the neutral.

Current Level Probable Effect On Human Body
1 mA Perception level. Slight tingling sensation. Still dangerous under certain conditions.
5 mA Slight shock felt; not painful but disturbing. Average individual can let go. However, strong involuntary reactions to shocks in this range may lead to injuries.
6-16 mA Painful shock, begin to lose muscular control. Commonly referred to as the freezing current or let-go range.
17-99 mA Extreme pain, respiratory arrest, severe muscular contractions. Individual cannot let go of an electrified object. Death is possible.
100-2,000 mA Ventricular fibrillation (uneven, uncoordinated pumping of heart). Muscular contraction and nerve damage begin to occur. Death is likely.
2,000+ mA Cardiac arrest, internal organ damage, and severe burns. Death is probable.
Source: OSHA

ELCIs can be installed both on the shore power pedestal and on the boat. Each installation location serves the same basic purpose but installing one on your boat ensures that your boat won’t ever leak dangerous current into the water and also gives you confidence your vessel shouldn’t have any trouble when you plug into an ELCI equipped shore power pedestal. An ELCI breaker is preferred for shore power circuits because of its ability to detect more faults than a GFCI. However, the use of an ELCI for the shore power circuit doesn’t remove the need for individual GFCIs in their typical locations around any potentially wet areas.

Why was the breaker tripping?

The offending panel with power flowing

As I mentioned above, these boaters worked with multiple electricians to resolve their issues but were still having troubles with ELCI equipped marinas. I was fortunate to visit the boat while it was at a marina — Burnham Harbor in Chicago — with ELCI equipped pedestals — and this was a major factor in being able to determine the root cause. This allowed me to see the issue happen, form a hypothesis about what was wrong and then test it out.

The electrical panel above is original to their boat, but the wiring behind it has been modified in a way that’s not obvious at first glance. There’s now an inverter — mounted in a closet in the aft master stateroom — with its hot, neutral, and ground directly connected to the respective busses on this panel.

The presence of the inverter immediately attracted my suspicion that it was causing the issues. Inverters and reverse Y-adapters are the most frequent causes of ELCI nuisance tripping. A look around the boat revealed there were no breakers to isolate the inverter, so to test this theory I disconnected the inverter from the back of the AC panel. With inverter removed the boat was able to draw power from the marina without issue. Reconnecting the inverter immediately tripped the ELCI.

With the culprit identified the question of why was left unanswered. Some research, contemplation, and discussion with people far more expert than me leads to a theory that makes sense to me. I believe what’s happening is actually a problem of timing.

Remember in the basics section above where I said the difference in electrical systems on a boat becomes a complication when we start generating our own power? Well, here’s that complication. ABYC A31 says: – The inverter/charger output neutral shall be grounded at the inverter/charger only when the device is the AC power source.

So this means the inverter has to create a tie between neutral and ground when power is coming out of the inverter and break that tie when it’s coming from shore power. That’s because your boat isn’t a sub-panel any longer as the inverter or generator is the primary source of power. Many inverters do this using relays, including the one onboard this boat. When there’s shore power coming into the inverter the relays are energized and that causes them to break the tie between neutral and ground. But, before those relays could receive power and break the tie the shore power breaker in the pedestal was seeing a fault condition (because of the tie between neutral and ground on the boat) and tripping the breaker.

The remedy

The inverter was installed by a previous owner many years ago and worked fine since it was installed. While it may have worked fine I don’t think it’s been working safely. Fundamentally, I believe this inverter was badly installed and has created some real hazards.

The first step I suggested to allow the boat to draw power from an ELCI equipped pedestal was to add a breaker to the output side of the inverter. This allows isolating the inverter from the AC panel which obviates the ground to neutral issues when connected to shore power. It also allows a quick and definitive way to ensure no power is flowing from the inverter onto the panel. The boat owners were able to have a yard install the breaker pictured above the following week.

It’s taken me a while to fully realize the ways in which this installation is dangerous. Because the output of the inverter is directly connected to the main panel there’s no back feed protection so if the shore power breakers are on the shore power cord itself will carry current from the inverter. There is a multitude of other issues with this installation all stemming from an inadequate installation. These issues are best addressed by having a qualified electrician review the inverter installation.

Final thoughts

As I worked through these issues I’ve been very concerned that multiple professionals have been on this boat and over the electrical system. I would have guessed that they would have highlighted some of the issues I saw, but I wasn’t there and I don’t know how thoroughly they went over the system and the particulars of the work they performed.

But, for me, it only takes one read of the story of Lucas Ritz, a 10-year-old boy killed by ESD, to invigorate the desire to call out unsafe conditions. It’s important to mention just how receptive these boaters have been when I’ve mentioned concerns. The safety issues that exist on their boat aren’t there because they don’t care about them, they’re there because they don’t know about them. So, although their tripping of shore power pedestals wasn’t because of current leakage into the water, it certainly did highlight some very important issues.

Additional Reading:

This article was syndicated from Panbo


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