The Offshore Voyaging Reference Site

Check Your Boat Shore Power System

Over the years I have bought three boats fitted with a shore power system and all of them were primed to kill, including our new-to-us J/109.

Sorry, I know that’s a dramatic first sentence but, seriously, this is scary stuff.

In the first two cases the problems were sins of commission where the AC system was wired incorrectly, but with our latest boat the problem is sins of omission, in that, although Tillotson Pearson wired the boat to ABYC recommendations properly when they built her 17 years ago, stuff has failed since then and not been fixed, leaving a situation that is, in many ways, the most dangerous of the three boats.

The point being that even if the new-to-us boat (or even brand-new boat) we buy was originally wired correctly, there are some things to check before we plug the boat into shore power.

So let’s dig into what those checks are, take a look at the truly scary shit I found, and then the fixes:

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Marc Jackson

I can understand the frustration about poor workmaship. Being a hardware store manager, I have observed the almost complete lack of ownership mindset that most people have. We live in rural America and customers are shocked when I tell them they are their own water utility company when it comes to water problems. They are frustrated at the inconvenience breakages give and at the same time unwilling to own their “crap.” Once you decide to truly own your stuff and get past that “someone else is at fault” loop, taking steps to minimize future frustrations look possible. It’s actually empowering once you swallow that big pill.

Not a boat owner, but those wires above the breaker look like they are touching the bolt above. Serious lack of wiring protection in that area, period. Cheers, Marc

Vesa Ikonen

Hi John.
Regarding your assumption:

Think of an ELCI as a Ground Fault Interrupter (GFI) for the whole boat that will, I’m near certain² (assuming that the boat’s AC ground is fully bonded to her underwater metals), trip if the live wire shorts to the case of any equipment, even if the shore power ground wire is disconnected.”

You are correct, that is exactly what would happen – it would even happen if the neutral wire would short.
The reason is that an ELCI is actually a device that measures the current differential between the live wire and the neutral wire. When the difference is zero (meaning that all current flowing in the live wire goes back via the neutral wire), the ELCI does nothing, and current flows in a complete circuit as it should.

If the differential is above a threshold set by the manufacturer (30 milliamps in Europe with 230V systems), the ELCI trips, since current is flowing (leaking) outside the circuit, i.e. it is shorted.

In a fully bonded boat, any metal part should be a path to ground (well, water, in case the ground wire is disconnected, but anyways). If either the live or the neutral leaks to anything metallic that is bonded to ground, ELCI will see a differential and trip.
This obviously assumes that the ELCI is THE VERY FIRST device in the circuit after the shore power receptable!!!

A tricky situation might occur in a non-bonded boat such as mine:
a non-grounded metal object might become energised if a live wire touches it, but the ELCI will not detect that until a person touches it and something that is grounded, and completes the circuit. Think of a stanchion and a wet wharf. Even in this scenario the ELCI will very, very likely save your life, since the current that it allows before tripping is so low that it should not kill you.
We did try this in a lab with our electricity professor, and it worked fine (no, we did not touch the wires).

ELCIs have fortunately been mandatory on new installs on all shore power systems (and all wall outlets in kitchens, bathrooms and anywhere outdoors) for quite some time at least in Finland, and I hope that applies EU wide. They work very well in protecting you around water.

Actually, when we tested our boats ELCI with an electrical engineer friend of mine, we could not get a reading for the current needed to trip it, since the marina’s ELCI that was upstream was just that much more sensitive that it always tripped first 🙂

An ELCI costs very little money, and I think everyone with any AC on their boats should get one tomorrow.

Matt Marsh

Yep. The ELCI is a very clever little device. You just run both the AC Hot and AC Neutral wires through the hole in the middle of a small transformer core. As long as all current going out the Hot comes back through the Neutral, the total flux induced in the core is zero.

If there’s a current imbalance, i.e. if current going out the Hot comes back through any path other than the Neutral, the flux induced in the core will be non-zero. There’s a little electromagnet driven by the secondary side of the transformer core that pops the breaker open if the current imbalance exceeds the threshold.

Simple, very reliable, and a big boon to safety. Just make sure you get one that acts on both poles (as I think all marine-legal ones do); interrupting the Hot side only won’t save you if the dock is wired backwards.

(I might add that ELCI, RCD, GFCI, ALCI, LCDI are all just different names for the same mechanism, which can be integrated in a number of different ways, eg. as part of a main breaker, or in a receptacle, or as a standalone whole-boat device, or to protect just one circuit…..)

William Murdoch

Should the ELCI be installed on the boat; down stream of the dock cord, beyond the boat plug and boat cord socket, and downstream of maybe 10 feet of the boat interior wiring? Should it not be at the pedestal end of the dock cord? There, as a part of the dock cord, no on boat modifications would be required, it would be easier to implement, and it would provide protection not provided by an ELCI installed aboard. Of course, all marinas should provide an ELCI as a part of the dock pedestal, but until then, why not provide your own as a part of your boat’s dock cord? To me it looks like the “good, fast, cheap” solution to providing a 30mA leak to ground protection to my boat.

A50 ft, 30A cord with an ELCI at the dock end would provide what I think is better protection to my boat than an onboard ELCI.

I wonder what ABYC thinks of this solution.

Dick Stevenson

Hi John and all,
It may be of interest that many RV owners will use an interface device between the “shore power” pedestal and the vehicle. The worry is clearly not ESD, but rather the issues of surge protection and warnings about low and/or high voltage, polarity, ground problems and the like. RV parks often share with marinas poorly designed and poorly maintained electrical systems that get regularly abused by their visitors.
My best, Dick Stevenson, s/v Alchemy

Dick Stevenson

Hi John,
That difference is exactly what I meant when I wrote, “The worry is clearly not ESD…” Perhaps I should have been clear that I was referring to electric shock drowning, ESD.
My best, Dick

William Murdoch

I can get around the issue of a pig tail ECIL unit with its mid-cable plug and socket by buying the unit listed on the website I referred to with a 50 ft cable.

By replacing my existing (and old) 50 ft shore power cord with that cord, I’d also have little chance of having my shore power hooked up in a marina with a cord without a ECIL because I have never had a marina offer to hook up the boat with any cable other than mine

But, there is no avoiding the fact that the ELCI would be in an exposed and vulnerable location dangling in the shore power cord below the marina power pedestal.

Vesa Ikonen

By the way, it is very hard to imagine why anyone would spend $1600 on an isolation transformer and not spend $30 on an ELCI, since AFAIK an isolation transformer will not save you from a scenario that an ELCI will.

I am amazed that ABYC would exempt ELCI’s based on isolation transformers!

Does anyone know why on earth they do?

Ernest E Vogelsinger

Hi John,
on my boat I installed an ELCI device like this:
Trips on overload above 16A, and on a ground fault delta of 30mA. No need to install expensive (300+) devices as they don’t do anything else, especially if you have mounted them in an according IPx casing.

Vesa Ikonen

Hi John.
I got mine from wholesales, and forgot to translate Euros to Dollars. Seems that hardware stores ask more like 50-80 USD.
The thing is: you don’t have to go Bluesea on these things – just get a regular household RCD/GFI and install in a plastic casing that is at least IP54 rated.

DC panels and busbars are a different story, and with those, the most likely cheaper alternative is automotive gear which does not last around salt water – there I will happily pay for Bluesea.

Any reputable brand like ABB, Hager, Schneider or similar will do, as long as it handles the current you need (mine was 25A and is combined with a circuit breaker).
ABB calls these Residual Current Circuit Breakers

Proper casing and they do fine in a boat. Even cruise ships use them.

A GFI ’becomes’ and ELCI simply by making sure it handles all the current used downstream, and installing it right after the shore power receptacle – or the isolation transformer if you have one.

Vesa Ikonen

Seems like Mastervolt requires not just one but two GFIs when installing their isolation transformer:
one at the input, another at the output.
Sounds bulletproof.

John, when you mentioned the hazard of wiring the transformer incorrectly, did you mean that the connection between the output neutral & output protective earth is often skipped?

Matt Marsh

Worth noting: All of the insurance carriers we talked to while getting coverage set up for Maverick V advised that boats whose shorepower systems do not comply with current ABYC standards are uninsurable, period. They no longer accept “it complies with the standards that were in effect when it was built.” A transfer of ownership triggers an underwriting requirement to bring everything between the dock end of the cord and the main AC distribution panel up to current standards, including a marine-rated ELCI and main breaker with reverse polarity indicator, or else they will not extend any “afloat and navigable” coverage.

This may not be universal, but it is true of all the carriers we considered.

With that in mind, I would have no qualms about using “well, the AC system is probably uninsurable and X,Y,Z will need to be replaced either now or the day after I buy it” as a bargaining chip in just about any purchase of a boat where any of that stuff is less than perfect.

And, in any new design, I would – unless there is a very compelling reason to do otherwise – limit the AC shorepower system to just an isolated battery charger, and design all systems to run either from the DC main bus or from an inverter-powered AC bus that has no link to shorepower.

Ernest E Vogelsinger

Hi Matt,
with my refit I installed a “limited system” somehow as you described. I have two AC chargers that can be switched separately, but I needed some AC in the boat as there are outlets and a LED/AC lighting in the main cabin. This circuit is separately switchable, and the ground fault line is only connected to the bonding (steel hull) if the this circuit is enabled. This setup allows me to have the chargers running while still no AC aboard.

Ernest E Vogelsinger

Yup, absolutely, see also my other post here “unless you are an expert and really know your stuff”. AC is inherently dangerous, especially on the water. No one should “assume” to know what he/she is doing, it might be one of the last assumptions.

(BTW, my surveyor recommended my solutions to Pantaenius being “state of the art or better”. Just wanted to brag a bit about it 😉 )
In Europe there is no ABYC but we have all these ISO and CE stuff. For AC, not a lot of difference except that a lot of things (ELCI for example) are required rather than recommended.

Alan Sexton

Hi John, marine electrical installations in Australia and NZ are covered by AS/NZS 3004 part 2, 2008 & 2014.
An earth leakage breaker is obligatory both on the vessel’s connection point to shore power i.e whole boat protection and then further ELCB’s are required for outlets around the vessel, these must be downstream of any onboard power source (inverter or generator).
In NZ any boat connecting to shore power must be inspected by a licensed electrical inspector every 4 years with a certificate (called an EWOF – Electrical Warrant of Fitness) being issued. Same applies for Motorhomes and caravans connecting to the mains- they have a separate standard.
We do have some grey compliance areas for boats built pre 2008, and this requires the inspector to apply some judgement, some of whom have been a bit over the top.
Every new production boat arriving in NZ from Europe has to have its AC (and LPG) installations upgraded to comply with the local standards

Dan Manchester

Is that an RF cable running across the GI and other AC cables, will give a nice buzz on your VHF?

My set up is a 120 V boat in a 240 V world; fortunately the isolation transformer acts as a stepdown transformer and I believe it still provides the required protection and dual voltage. I would do the full conversion but it would mean new inverter, new gererator, new Aircon, a whole bunch of powertools becoming paperweights, and for no real gain for what we really use onboard. If someone would just send me a 120 V nespresso machine, I’d be set!

Dan Manchester

Thanks John, yes, the aircon situation is annoying and as a result not operated very often except when I’m onboard dockside doing sweaty maintenance in the summer.

Related question; is it safe to use a portable generator through the shore power inlet to an isolation transformer? I assume only the run from the generator to the transformer is essentially unearthed, or do generators have their own earth somehow?

Ernest E Vogelsinger

A generator, whether in the power plant or on board, always generates a potential difference between two conductors. In a power plant, one of these conductors is always the “real” earth/ground, whereas a generator of course has no “earth”. With a line from the power plant, you can touch “neutral” without any problems, but never the “phase” (if you are standing on the ground). With a line from a generator you may touch each conductor separately because there is no potential difference to earth – but never both at the same time. You can of course define one line of the generator as “earth” and connect it to the bonding system, but I would strongly advise against it, unless you are an expert and really know your stuff. What must not happen is that the generator gets a connection to shore power.

Ernest E Vogelsinger

A portable generator must never be used as power source for an AC network (like in a house, or a boat).
[Edit – it is perfectly benign if the portable gen powers an isolation transformer only]
The reason is that a portable generator has no earth-neutral and as such no ground fault capability. In technical terms but simplified a portable gen provides an ungrounded IT network, while shore power (and a correctly installed inverter) provide a grounded TN network. If interested the different network types are discussed for example here:,_TN_and_IT_systems
Note: electricians study this topic years long for their final certificate, so no DIY should try to mess around with this, just leave it to the pros. It cannot, however, be wrong to be educated so one can distinguish between the “real” pro and the usual cable splice guy (no offense meant)

Dan Manchester

The above scematic was left to me by the previous owner who I believe was an electrical engineer and might help with your thinking it through. I have a selector switch installed to choose between 110 generator, 240 shore, or 110 inverter. I only get dual voltage on shore power. It looks like the boat side earth runs through everything, but doesn’t explain the generator before the inlet.

Dan Manchester

Hi John, actually this is the drawing of the set up for a portable generator through shore power, which is the set up I have. There is a selector switch, as per the dotted box, but I’m unsure if this does anything to the earth when moved from shore to generator.

Ernest E Vogelsinger

Sorry, but I wouldn’t really recommend this setup.
First, when using the genset (1,3) according to the drawing there is no ground fault line at all, or at least the GF line emerging from the transformer is not shown.
Next, the genset feeds into the transformer secondary. If this is an “old school” transformer based on windings on an iron core this is bidirectional, so the genset would induce current on the shore side of the transformer, which would power the (possibly open) shore plug. A dangerous situation.
In case of a modern HF transformer it would most probably burn the electronics, or at least trigger the internal breakers.

Why not power the transformer from the genset? this would circumvent these issues.

Dan Manchester

Hi John,

I was going to comment to mention this but you’d closed off comments.

The portable generator goes through the shore power inlet, through a double pole breaker, to the ISO transformer, then to a selector switch, which has Shore/gennie/inverter options. I think the selector switch chooses which outputs from the iso transformer (or the inverter) to supply to the switchboard. Noting I have a dual power switchboard supplying 120/240 when on 240 shore, but only 120 when on 120 generator.

I’m certain this is a fairly unique installation, driven by the PO’s being British, refitting the boat in the US, and intending to sail it home (though only getting to australia), so wanting a versatile dual power system.

I’d like to swap out the 120 V gennie to a 240 V version to give me dual voltage at anchor so I can run the water heater, I just don’t want to introduce a safety risk by doing so. This thread has helped rationalise that thought process and lead me to think there is no greater risk.


Dan Manchester

Hi John,

Thanks, I fully appreciate how difficult it is to give an opinion on something from a dodgy sketch and a bad description! If nothing else this exercise has made me think about and look at the AC side of my boat considerably deeper than ever before. Knowing how it works in practice, I do now have a reasonable level of confidence that it is doing what it is meant to, whether it meets AS/NZ code may be a different question. I work with a bunch of marine electricians, so will ask one to take a look; though if you ask the same question to 5 electricians you’ll get 6 different opinions…

Ernest E Vogelsinger

John, a portable generator delivers no “neutral” but merely two phases with 120V (or 240V) potential difference. One of these phases is usually connected to the ground fault connector(s) at the gen plug(s), but this only helps if the gen and whatever is plugged in share a common “ground” where a fault current can pass between gen and its client.
Some gens come with a ground hook you’re supposed to drive into the ground but this might be unwise to do on a boat. So the only way to use a portable gen for general onboard AC is as you say via an isolation transformer (wired correctly).
Similar issues arise with inverters, but I won’t cover them here 😉

Alex Borodin

I am absolutely unqualified to make comments about safety of electrical systems, so that’s exactly what I’m going to do now.

Looking at that photo, I’d be worried that there seem to be AC and DC conductors passing through a bulkhead not protected from chafing and not isolated from each other by a conduit.

Alex Borodin

> When AC and DC conductors are run together, the AC conductors shall be sheathed, bundled, or otherwise kept separate from the DC conductors.

I guess this means a conduit is not required. Told you I’m unqualified 🙂

James Greenwald

Dear John and Vesa,

Currently in the final stages of updating our entire charging AC/DC, storing and monitoring systems. (1988 Swan 53) I have been informed by our ABYC designer and installer that with our Victron isolator, along with a residual current device (RCD) or a ELCI will suffice to meet Victron’s design and installation standards. ( we have an RCD)

James Greenwald

Hi John,

Perhaps I was not clear we did install an isolator transformer and have an RCA boat side. I believe RCA/ELCI are basically the same? For sure my personnel weak points have been the refitting the electrical systems and have relied on outside boatyard assistance. Which as you correctly point out do not always have my best interest and safety in mind. RANT……. I am consistently riding them on taking care of these details, which for what I am paying they should be managing themselves. P.S I hate them all 😉

James Greenwald

Really! I would like to know more to the subject. I thought Isolator Transformers are fairly straight forward.

James Greenwald

Misspoke; no galvanic isolator only isolation transformer. For sure eliminates the need for galvanic isolators and polarity alarms.

James Greenwald

Also to the shore side connection we have gone with the SmartPlug Which as understand is a vast improvement in shore power connection and safety.

Ernest E Vogelsinger

you don’t mention polarity although this is as well important.
I just refitted the complete AC system on my boat after purchase, and installed a Philippi polarity monitor. The AC master switch has two “ON” positions, where “1” passes phase/neutral unmodified, and “2” exchanges phase/neutral. So if you come around an incorrectly wired post the monitor would show red instead of green, and all you have to do is to use master position 2 instead of 1.

Ernest E Vogelsinger

Uh, well, I should make a habit of not skipping parts of the article – of course you did, I just skipped that expensive BlueSea monster 😉
Of course you’re right in pointing out that a mistake can be made, however this would immediately show up in having the polarity monitor being bright red instead of green, cannot be overlooked as the monitor is located immediately above the switch. Additionally this monitor shows if the ground fault wire is connected correctly – if there is no connection both lights (red&green) are illumniated simultaneously. If this is the case my governance dictates that AC must not be switched into the cabin, but the chargers (being fully isolated and having no ground fault line anyway) can still be used.
All this for less than 50 bucks if I remember correctly.

Ernest E Vogelsinger

Wilco 🙂
Just need to rearrange miscellaneous structures (such as the engine) to make room for that… 😉
Seriously, I did consider (in fact still am) but at the moment there are more important things on the list, the AC system being thoroughly tested and ok’ed for now.

Ann Bainbridge

A year and a half ago we paid only $720 (USD) for a Victron isolation transformer (3600W). Worth every penny. The Victron transformers also do voltage conversion (115<->230V) which, at the time, the Mastervolt isolation transformers did not.

Dan Manchester

I’m going to have another guess: is it that the equipment appears to be in part of the bilge, which is a really silly place to put electrical equipment?

Alex Borodin

Looks like up under the deck-hull joint to me. But if it’s the bilge, then oh, boy…

Dan Manchester

Could be right, in which case I change my answer to that centre bolt appearing to be galvanised and starting to corrode. As well as the entry gland for the breaker being at the top and right under above mentioned dodgy bolt.

Dan Manchester


Kevin McNeill

Re the photo, the shore power leads are resting on a bolt end and unprotected, not a good scheme.
The shore power for our boat, an elderly Irwin 37, come aboard and goes through a hydro meter. From there it goes to two things, the battery charger and the hot water tank, all else is done through the inverter.

Ernest E Vogelsinger

Ah wait – did you say you’re running the calorifier from shorebased AC, and the rest of the boats AC from an inverter?
I’d say this is inherently not ok except when you NEVER use the inverter when docked and plugged in, ’cause a fault that would connect shore power with your inverter wouldn’t be desirable.
Basically the rule is to never have more than one single source of power, the others inaccessible by design.

Ernest E Vogelsinger

This is true for combined devices (charger/inverter), but a “normal” inverter hooked to the battery bank has no idea if there is shore power live or not. Therefore strict provisions must be taken so the inverter can only be started when shore power is completely disabled.
Additionally: with shore power (w/o isolation transformer) the ground fault line must be connected to bonding when shore power is active. This connection MUST NOT be in place when the inverter is running, usually the inverter case will be “grounded” then (depends on the inv make).

Stein Varjord

Hi John,

Again an important topic that is almost neglected in most boats. I’ve made sure all this is good on our boat, but have no isolation transformer, yet. It’s an interesting topic. I see Steve D’Antonio and others have also pointed out that a lot of isolation transformers are installed in dangerous ways, especially how they may effectively disconnect the boat from the shore ground system, without a good alternative.

I’m not yet comfortable enough with my own understanding of the topic to make a decision, but I consider getting one of the Mastervolt isolation transformers you mention. Looking at their texts and data I get some (maybe unfounded) questions. In their first sentence of the description they use the words “galvanic isolation”, which is a whole other thing than an isolation transformer, of course. The product name is “Mass GI 3,5”, where I assume GI is for galvanic isolator?

I also notice that Mastervolt has another product with the same capacity that weighs in at 5 times as much, 30 kilos, even though that one is a stripped version, no cabinet etc. There one can visually confirm that it’s an actual transformer with coils and all. They still use the same words in their description, though. Galvanic isolator.

Is this a case like when the old type battery chargers with coil transformers were replaced by electronic transformers with dramatically reduced weight and size, plus far better performance? Or is it two different types of product confusingly put in the same group because they are applied to the same type of problem, galvanic corrosion prevention?

Ernest E Vogelsinger

Hi Stein, of course an Isolation Transformer galvanically decouples the boat from shore as well. The GI 3.5 and GI 7 are in fact full blown isolation transformers and differ only in power.
The issue is that a transformer can be used in two different ways (isolation or polarization), and this is often grossly misunderstood – for our requirements full isolation mode is required.
There is one drawback in using an IT, being that the shorebased line passes through the boat but is not grounded in the boat (must not!), so a fault in the supply line aboard before reaching the IT can wreak havoc. Actually this is the reason why the supply line must have an ELCI + breaker as close to the shore plug as possible to minimize such a risk.

Stein Varjord

Hi Ernest,
What I wondered about is the difference between the GI 3,5, and the IVET 3,5. They both have the exact same output, 3,5 kW:

Since they are both touted as isolation transformers and both description texts seem to say, vaguely, that they work mostly the same way, I wonder why one weighs 6 kilos, and the other weighs 30 kilos, 5 times as much as the other while giving the same 3,5 kW power. The latter heavier version is even in a “naked” edition, without the slow start included.

My only way of explaining this is that either they are:
– Different types of tools doing a different job.
– Different generations of tech doing the same job.
– Some other explanation?

Rob Kuder

Hi Stein,
I’m no expert but – same job, different tech. The GI 3.5 is a modern high frequency switching converter while the later is an old school iron core transformer. Interesting to me is that the GI 3.5 will only put out 1.9kW @ 120V because it is limited to 16A.

Ernest E Vogelsinger

Of course you’re right John – however I meant the line from the shorepower plug on the hull to the inverter. This is basically ungrounded shore AC and must be treated as such, thus the “ELCI as close to the plug as possible” recommendation/requirement.
Usually it is sufficient to have this cable completely sheathed from plug to inverter (except the ELCI connections of course).

Michael Iannicelli

Another Reason to Upgrade to an ELCI – Finding Faulty Equipment.

I updated a friend’s 40-year-old Morgan with two, 30-amp shore power circuits feeding 2 AC subpanels. We replaced the two original main breakers with a dual ELCI panel from Blue Sea (model 3117). I liked the Reverse Polarity indicators and the water resistant housing which is mounted in the engine room. Blue Sea’s documentation is great and the installation was straightforward.

After connecting the shore power cables and energizing both breakers, one immediately tripped. We could only energize one 30-amp circuit at a time. After hours of troubleshooting, we found the AC rotary selector switch (Shore/Off/Inverter) was leaking current between the AC subpanels. We did not try and measure the leakage, but it was obviously greater than the 30ma ELCI trip point. After replacing the Rotary switch (another Blue Sea item – I’m a fan) everything worked as designed. 

I consider myself fortunate for finding the current leakage during the upgrade. I could have been seriously injured while troubleshooting a subpanel thought to be de-energized. 

Michael Iannicelli

For your sanity, I hope not. What lead us to finally suspect the Rotary selector switch as the problem, was Not being able to clear the fault by isolating any of the Panel circuit breakers. I wish you better fortune.

Vesa Ikonen

One hint if the ELCI trips immediately after powering on and plugging something in:
check that the neutral wire (the complete circuit) actually runs back through the ELCI. I have seen it happen several times that a device that has its live wire fed through the ELCI has its neutral bypass the ELCI, thereby making the ELCI trip as it sees a current imbalance.
This typically happens in distribution panels where some devices are fed by an ELCI/GFI and some directly from a circuit breaker with no GFI, with separate neutral busbars for each circuit but with one neutral wire connected to the wrong neutral bus, so this should not happen on a boat with an ELCI upstream of all AC distribution, as all neutral wires should terminate at an ELCI or a single neutral busbar connected to one.

Still, this situation might be tricky to troubleshoot, since it is really not a dangerous fault although the ELCI will make it seem that way (no device is broken or miswired, and you are not at risk, it’s just nuisance tripping the ELCI the second you connect something to the receptacle).

In this scenario the ELCI trips when you plugin a device that consumes power in any receptacle downstream of it, but it should not trip by merely plugging in the shore power cord with all consumers disconnected.

Terence Thatcher

Wow. What I don’t know could hurt me. The through hulls on my boat are not bonded. I have considered doing that, but it is quite a task. It sounds as if a good first step, nonetheless, is to have a certified electrician install an ELCI. Thanks.

James Kevern

Re: portable generators. As John noted they can be used at houses when fitted with a change over switch to connect neutral to ground. In a marina the ground connection is somewhere on shore, which is why the inverter charger has relays that connect them when in invert mode, but disconnect and pass through in shore power mode. From the Victron Multi user manual:

The MultiPlus is provided with a ground relay (relay H, see appendix B) that
automatically connects the Neutral output to the chassis if no external
AC supply is available. If an external AC supply is provided, the ground
relay H will open before the input safety relay closes. This ensures the
correct operation of an earth leakage circuit breaker that is connected to
the output.

Our solution back in the days when we had a portable generator was to take a plug from the hardware store, jumper white to green and plug that into the receptacle on the generator. This provides the grounding that ordinarily occurs somewhere on shore. The indicator that this was needed in our case was the reverse polarity light flickered without the grounding plug in place.

However I will provide the same caveat – I’m not a trained electrician or electrical engineer, so it’s possible, if not likely, that there is some reason this is a bad idea. As others said, the isolation transformer is a more fool proof solution.

James Kevern

One other point – newer marina installations in the US have ELCI’s or Residual Current sensing breakers in the shore power pedestal. The new section in Fort Pierce FL had those and routinely had boats come in that would trip them. Our brand new Outbound 46 did, and an electrician finally traced it to a sliver of metal left between the neutral and ground connections on the water heater (which looked to me like a manufacturing artifact to prevent welding current from going through the heating element). And this was a well respected first world brand. We were fortunate to discover that early in our ownership of that boat.

Loic Robineau

Great article thank you! Like probably a lot of us, I am a total newb in electrical boat system. Can you recommend some great book to learn from the start ?

john stanley

Hi John

I use a socket test plug at the marina post before I connect. This avoids the danger of connecting to a faulty or reversed supply and having to get back on the boat to check what the panel is telling you.
I also plug my own inline RCD at the post and plug my coord into that. This not only protects the boat but also if the insulation on the cord is damaged and someone stands on it with wet feet on the dock.
Finally I plug in the socket tester in the boat to confirm all is ok.
Of course you still have the issue of needing to prove the correct operation of your tester, so perhaps a second for an periodic check.


Brown Bear

john stanley

Hi John, here is a link for the one I use at home, although I have an american boat it was supplied to the UK so is kitted out with 13 amp 3 pin sockets. These test plugs are available in all pin configurations in whichever country your boat is from.
I would presume this would Identify a fault in a galvanic isolator (open circuit) when used in an onboard socket?



Michael Thompson

We have just been working through electrical system checks and improvements on a second-hand 38 foot yacht (1986) we purchased. Shore power connector was loose (replaced it), some wiring in 12v DC system had been connected with electrical tape in past DIY repairs (had a marine electrician crawl over every wiring join and do it properly), we had a 240v compliance test done (we are in Australia) – all passed OK and feel like we can sleep at night knowing it’s all correct. Now checking re situation on galvanic isolator as still learning – that’s the next job and will probably have new one installed. We don’t keep the boat plugged in to shore power when we are away – solar power keeps batteries topped up for bilge pumps and fridge, everything else switched off. Although just about to install a BRNKL also to remotely monitor certain systems.

Paul Kanev

My Hinckley had paired 30 amp shire power cord systems. One for AC, the other for everything else. Each is connected to a vectron 3600 isolation transformer
We plan a transatlantic from Bermuda after the 2022 race to azores and in turn to Scotland
Where did you source and supply shore power cords for UK and EU for dock hookup?
Many thanks

Dick Stevenson

Hi Paul,
Mid-Atlantic Yacht Services in Faial will be able to do and/or supply most anything you want along those lines. Contact ahead of time for assurances.
If planning to be there for period of time: we had a small EU/UK power panel installed with circuit breakers for 2 receptacles and a battery charger (using a full range of voltages and hZ). I also had a EU/UK shore power inlet. This allowed use of local appliances such as de-humidifier (very nice as you live closed up more than many cruising locations) and space heaters. It simplified living and cruising on the boat during our years in Europe/UK a great deal.
My best, Dick Stevenson, s/v Alchemy

Ernest E Vogelsinger

Re “testing ground continuity” – there is a really smart little gadget from Philippi that will show you immediately if your shore power connection is fine (green LE), reverse polarity (red LED), or if the ground connection is missing or has failed somehow (both LEDs).

Dick Stevenson

Hi John,
I have called ABYC and they report no membership below $275 USD per year, a “business membership” and no individual membership at $190/year. Did I miss something?
And even at $190/year, I do not suspect I would wish to consult the standards more than a handful of times.
I do very much want to support ABYC and I make a point of asking every boatyard I come into whether their techs are ABYC certified and think it would make a difference if everyone did this.
My best, Dick Stevenson, s/v Alchemy

Dick Stevenson

Sure does. Thanks, Dick

Dick Stevenson

Hi John,
A follow up on ABYC membership:
I twice reached by phone the ABYC membership coordinator who kept saying there was no membership for boat owners. Earlier today I have talked with her and she has now acknowledged the recreational boater’s membership for $190 per year. Not sure still what the confusion was.
There is an industry vs recreational tree/crossroads to their web site and the default seems to be industry oriented and that was another rabbit hole I kept inadvertently going down. So I ended up on the part of the site which, of course, did not address recreational boaters.
Thanks for the help.
My best, Dick Stevenson

Kevin Towers

I have a thirty year old boat that was completely re-wired 12 years ago. Unfortunately, they never included a galvanic isolator or a ELCI in that project, so I’m looking to correct that now.
Thinking about how galvanic isolators are sized, they are designed to take the complete fault current until the main or sub breaker trips. That means a 30A breaker should have a minimum of a 30A isolator. But with a ELCI installed, the ground wire should never see more than 30mA before the ELCI trips, so sizing a galvanic isolator for 30A is an overkill and waste of money. Thoughts?

Dave Warnock

Just checking on naming as it took quite a lot of googling.

Am I correct that for Europe (well at least the UK) when you talk about ELCI breakers that is the same as RCD breakers that we use?

If I am correct would it be possible to add a note to the text as searching for ELCI products in the UK doesn’t find much.


Tom Irwin

John, late to the party on my read of this but better late than never. I just resubscribed , thanks. In your article you test continuity of the shore ppower ground. You state “ from the ground pin on the unplugged dock end of the boat’s shore power plug to the shore side lug on the isolator. “. My new galvanic isolator , just like yours, is installed in a stern locker accessed below through my aft cabin. How do you physically “ connect your meter” between the shore side lug of the isolator in the aft cabin locker and the ground pin on the boat’s shorepower socket which is located on the outside aft bulkhead/ stern scoop . These twopoints are just feet apart but separated by the deck ! I am sorry i am either ignorant or misunderstand your instructions.

Brian Underhill

Fascinating and informative article as always John, thank you.

Re Galvonic Isolators (GI), when used in conjunction with an ELCI, am I right in thinking the GI should be installed as close as possible to the shore power inlet plug and the ELCI must be within 10ft of said inlet plug?

In other words, the GI is installed on the ground wire prior to the ELCI and not after it?


Brian Underhill

Thank you for the prompt response John!