Where to locate Galvanic Isolator

[Sailorlou]

Originally Posted by Ahmet Erkan

Dear Sailorlou,
In our community, sailors need to consult with the electrical experts like yourself and get their advice on electrical matters.
Please care more, and explain the product you are evidently recommending for our boats.
I was unable to find a "clear diagram" in the manual. Elaborate instructions and warnings say do not connect the "earth ground" to the "protective earth ground"
Is there a galvanic isolator (ie: inverse parallel diodes) inside the transformer case? Is the "earth ground" or the "protective earth ground connected to the chassis of the enclosed transformer? No instructions state where the "protective earth ground" should be connected.
Could you please explain why we should trust this manufacturer with our lives and feel safe by connecting wires into six terminals inside their magic box that the manual does not say where the wires go and not know where to connect the "protective earth ground" external to the transformer?
I apologize if I came across as pontificating, but if possible lets leave that behind us and try to give the best and most accurate advice to our fellow sailors.
Thank you.
Ahmet

OK Ahmet,

Glad to hear you are open to leaning more about isolation transformers and how they operate. The problem I have is that I do not like to spend a lot of my time educating people on electrical theory through an on-line forum.
The best way for you to learn what you are asking is to take the course offered by ABYC. You can contact Kevin Ritz directly through the web links I posted before. I am sure Kevin would be more then willing to point you in the right direction.
At this point I am not going to go into a long description of Isolation Transformers or galvanic isolators.
I will simply state that if you have an isolation transformer installed and correctly wired you do not need a galvanic isolator. The two do not work in conjunction with each other because a galvanic isolator requires you to connect the shore ground to the grounding system on your boat through the galvanic isolator, it does not break the ground connection between the shore and the boat. The isolation transformer protects your boat by breaking the physical connection of the ground, neutral and hot leads. These are given facts.
If you want to learn in detail how they are constructed and the theory behind their operation, you can either research it on the web, read books or take the ABYC class. I'm not trying to say you have not already done some studying, you obviously have to some extent. Maybe you just have either some misunderstanding or misconceptions or have been advised wrongly.
Sorry, I just don't want to spend the time, I would have to write a book and I really don't like to type that much. Try reading "The Boatowner's Guide to Corrosion" by Everett Collier. Also check out "Boatowner’s Mechanical and Electrical Manual" by Nigel Calder.
Also you must realize, that usually the wiring instructions put out by manufacturers have to be thoroughly researched because they can be held liable. Especially when it comes to important protection devices such as we are discussing. Good luck to you in your research.

[Ahmet Erkan]

Originally Posted by Sailorlou

OK Ahmet,

Glad to hear you are open to leaning more about isolation transformers and how they operate. The problem I have is that I do not like to spend a lot of my time educating people on electrical theory through an on-line forum.
The best way for you to learn what you are asking is to take the course offered by ABYC. You can contact Kevin Ritz directly through the web links I posted before. I am sure Kevin would be more then willing to point you in the right direction.
At this point I am not going to go into a long description of Isolation Transformers or galvanic isolators.
I will simply state that if you have an isolation transformer installed and correctly wired you do not need a galvanic isolator. The two do not work in conjunction with each other because a galvanic isolator requires you to connect the shore ground to the grounding system on your boat through the galvanic isolator, it does not break the ground connection between the shore and the boat. The isolation transformer protects your boat by breaking the physical connection of the ground, neutral and hot leads. These are given facts.
If you want to learn in detail how they are constructed and the theory behind their operation, you can either research it on the web, read books or take the ABYC class. I'm not trying to say you have not already done some studying, you obviously have to some extent. Maybe you just have either some misunderstanding or misconceptions or have been advised wrongly.
Sorry, I just don't want to spend the time, I would have to write a book and I really don't like to type that much. Try reading "The Boatowner's Guide to Corrosion" by Everett Collier. Also check out "Boatowner’s Mechanical and Electrical Manual" by Nigel Calder.
Also you must realize, that usually the wiring instructions put out by manufacturers have to be thoroughly researched because they can be held liable. Especially when it comes to important protection devices such as we are discussing. Good luck to you in your research.

Dear Sailorlou,
This is not a P... race :-)
There is no doubt in my mind that a shielded isolation transformer has a significantly better performance in galvanic isolation compared to adding a few diode drops between the "shore power grounding conductor" and "hull ground". Again, my concern is not with the isolation capability.

It is my belief that recommending the boaters to break the connection between their hull ground and the shore power grounding conductor is unsafe. I have already explained the reason for my concern multiple times. ELCI devices are not guaranteed to be present at the dockside or on board many boats. Even if an ELCI of GFCI device is present it does not warn the operator if it has failed. Therefore the diver below or the swimmer around the boat is subject to a system with a "single point failure" preventing him or her from death. The single point failure is shorting of the shore power hot conductor to the hull ground. Especially in a fresh water environment, if this failure happens people will die. Actually they do die.
Please concentrate on the other virtues of the isolation transformer, I will help you do it if you let me. The classic galvanic isolator with inverse parallel diodes needs to evolve, especially in the monitoring and self testing areas but you have to admit it provides a level of safety, much greater than an isolation transformer coupled with GFCI/ELCI devices. Ahmet

[Sailorlou]

Originally Posted by Ahmet Erkan

Dear Sailorlou,
This is not a P... race :-)
There is no doubt in my mind that a shielded isolation transformer has a significantly better performance in galvanic isolation compared to adding a few diode drops between the "shore power grounding conductor" and "hull ground". Again, my concern is not with the isolation capability.

It is my belief that recommending the boaters to break the connection between their hull ground and the shore power grounding conductor is unsafe. I have already explained the reason for my concern multiple times. ELCI devices are not guaranteed to be present at the dockside or on board many boats. Even if an ELCI of GFCI device is present it does not warn the operator if it has failed. Therefore the diver below or the swimmer around the boat is subject to a system with a "single point failure" preventing him or her from death. The single point failure is shorting of the shore power hot conductor to the hull ground. Especially in a fresh water environment, if this failure happens people will die. Actually they do die.
Please concentrate on the other virtues of the isolation transformer, I will help you do it if you let me. The classic galvanic isolator with inverse parallel diodes needs to evolve, especially in the monitoring and self testing areas but you have to admit it provides a level of safety, much greater than an isolation transformer coupled with GFCI/ELCI devices. Ahmet

Hi Ahmet,

I really have no desire to try and create an instructional class on this forum to educate people on boat electrical systems. There are plenty of sources in existing books and available classes for people to receive that information and training in depth. The best source in my mind would be one of the classes on the subject offered by the ABYC. Once again, people can contact Kevin Ritz at ABYC for information on their available classes.

I understand your concern on a possible short to the bonding system from the incoming hot lead on the power cord when you are protecting your boat using an isolation transformer. However, your approach of using a Galvanic Isolator in conjunction with an Isolation Transformer doesn't make a lot of sinse. With a Galvanic Isolator you preserve the shore ground connection to the boats' grounding system, with an Isolation Transformer you break that physical connection. If you use them together you defeat the purpose of the Isolation transformer. You could use them in conjunction as you describe, but the only benefit you get from having the Isolation Transformer in that scenario is that is would clean up any noise on the shore power side and possibly protect you from any spikes, depending on the design. But you don't need an Isolation Transformer to do that. You could instead just use a standard one to one or a buck and boost transformer. The buck and boost in your scenario would be the best choice because it would give you clean power and the ability to boost any low power from the shore or conversely step down any high power from the source. It would also allow you to do a conversion from 110 to 220 or vice versa. Depending of course on the design of the buck and boost transformer.
You can also get an Isolation Transformer witch can both isolate and provide buck and boost. Isolation Transformers do not have a Galvanic Isolator built in, they are not necessary and defeat the purpose of the Isolation Transformer. Galvanic Isolators only block DC stay current. They do not clean up the AC power, they do not block AC stay current, they provide no electric shock protection. There are Galvanic Isolators on the market which do provide a fault notification indicator light, but most available do not have this function.
Proper installation and maintenance of the incoming power cord will prevent the hot lead from shorting to the ships ground system ahead of the transformer, by making sure you use a marine grade shore power cord and make sure it is in installed in such a manner that you don't have a chafing problem and using proper strain reliefs and that your terminations are done correctly. The core itself and it's incoming and outgoing wires are insulated from the outer case of the transformer. You usually connect the neutral wire to ground at the Isolation Transformer, but this connection can be done at the panel. This creates your neutral source within the boat. With an isolation Transformer your neutral to ground connection is on the boat , because you break the physical connection coming from the source.. Therefore you also eliminate any reverse polarity problems that might occur because of improper wiring at the source.
Once again, the purpose of an isolation Transformer is to break the physical connection between the source and the boat, thereby protecting you from electrical shock hazards both on the boat and the water, plus protecting you from both AC and DC stray currents as well as providing a clean power source.
That's it, I've beat this horse to death, if you want more in depth information try one of the sources I have already mentioned.

Thanks and good luck.

[Ahmet Erkan]

Originally Posted by Sailorlou

Hi Ahmet,

I really have no desire to try and create an instructional class on this forum to educate people on boat electrical systems. There are plenty of sources in existing books and available classes for people to receive that information and training in depth. The best source in my mind would be one of the classes on the subject offered by the ABYC. Once again, people can contact Kevin Ritz at ABYC for information on their available classes.

I understand your concern on a possible short to the bonding system from the incoming hot lead on the power cord when you are protecting your boat using an isolation transformer. However, your approach of using a Galvanic Isolator in conjunction with an Isolation Transformer doesn't make a lot of sinse. With a Galvanic Isolator you preserve the shore ground connection to the boats' grounding system, with an Isolation Transformer you break that physical connection. If you use them together you defeat the purpose of the Isolation transformer. You could use them in conjunction as you describe, but the only benefit you get from having the Isolation Transformer in that scenario is that is would clean up any noise on the shore power side and possibly protect you from any spikes, depending on the design. But you don't need an Isolation Transformer to do that. You could instead just use a standard one to one or a buck and boost transformer. The buck and boost in your scenario would be the best choice because it would give you clean power and the ability to boost any low power from the shore or conversely step down any high power from the source. It would also allow you to do a conversion from 110 to 220 or vice versa. Depending of course on the design of the buck and boost transformer.
You can also get an Isolation Transformer witch can both isolate and provide buck and boost. Isolation Transformers do not have a Galvanic Isolator built in, they are not necessary and defeat the purpose of the Isolation Transformer. Galvanic Isolators only block DC stay current. They do not clean up the AC power, they do not block AC stay current, they provide no electric shock protection. There are Galvanic Isolators on the market which do provide a fault notification indicator light, but most available do not have this function.
Proper installation and maintenance of the incoming power cord will prevent the hot lead from shorting to the ships ground system ahead of the transformer, by making sure you use a marine grade shore power cord and make sure it is in installed in such a manner that you don't have a chafing problem and using proper strain reliefs and that your terminations are done correctly. The core itself and it's incoming and outgoing wires are insulated from the outer case of the transformer. You usually connect the neutral wire to ground at the Isolation Transformer, but this connection can be done at the panel. This creates your neutral source within the boat. With an isolation Transformer your neutral to ground connection is on the boat , because you break the physical connection coming from the source.. Therefore you also eliminate any reverse polarity problems that might occur because of improper wiring at the source.
Once again, the purpose of an isolation Transformer is to break the physical connection between the source and the boat, thereby protecting you from electrical shock hazards both on the boat and the water, plus protecting you from both AC and DC stray currents as well as providing a clean power source.
That's it, I've beat this horse to death, if you want more in depth information try one of the sources I have already mentioned.

Thanks and good luck.

Sailorlou,
I must admit that I have not read your previous replies but I did read this one in detail. You said and I quote "galvanic isolators provide no electrical shock protection". Oh my God, what you say is absolutely not true my friend.
The shore power grounding conductor (the green one) has a very important safety function and of all people a Electrical Engineer should never support throwing away this extremely important safety function.
We are not finished my friend. Because you are a EE, I am going to convince you to retract your present advice to the fellow sailors and tell them to maintain the shore power grounding conductor on board as an asset and use it clamp any lethal voltage surges of their hulls referenced to marina ground during a catastrophic failure and be able to perform this function because the boat is wired in compliance to the latest ABYC guidelines and the shore power grounding conductor is bonded to the hull ground of the boat. (via a galvanic isolator)

Sailorlou, you do not want to be responsible for the next swimmer fatality due to electrocution. Wake up my friend.
Ahmet

[Sailorlou]

Originally Posted by Ahmet Erkan

Sailorlou,
I must admit that I have not read your previous replies but I did read this one in detail. You said and I quote "galvanic isolators provide no electrical shock protection". Oh my God, what you say is absolutely not true my friend.
The shore power grounding conductor (the green one) has a very important safety function and of all people a Electrical Engineer should never support throwing away this extremely important safety function.
We are not finished my friend. Because you are a EE, I am going to convince you to retract your present advice to the fellow sailors and tell them to maintain the shore power grounding conductor on board as an asset and use it clamp any lethal voltage surges of their hulls referenced to marina ground during a catastrophic failure and be able to perform this function because the boat is wired in compliance to the latest ABYC guidelines and the shore power grounding conductor is bonded to the hull ground of the boat. (via a galvanic isolator)

Sailorlou, you do not want to be responsible for the next swimmer fatality due to electrocution. Wake up my friend.
Ahmet

Ok, I must admit I wrote that in a hurry and didn't go into the detail I should have. Most Galvanic Isolators on the market do not conform to the ABYC recommendations. These products do not provide the protection from electric shock on a fault. You must have a Galvanic Isolator that conforms to ABYC recommendations and be in another class altogether called a "Fail Safe" Galvanic Isolator.

Below is an explanation.
This is information from DEI Marine which manufactures what I believe are the best and safest Galvanic Isolators on the market. Their products are what is Known as "Fail Safe Plus" and Fail Safe Max" and don't require monitoring. Most on the market do not meet this criteria. The "Fail Safe Plus" is over $300.00 and The "Max" is over $400.00. In my opinion that money can go a long way to afford an Isolation Transformer.

"Galvanic isolators, and products that perform the
same functions for land-based applications have
an extensive usage history. Land based products
called decouplers are commonly used in the general
corrosion protection industry, where it is necessary
to prevent the flow of dc current while providing ac
continuity, the same function performed by galvanic
isolators. All such decouplers, when used in the
grounding path of electrical equipment, must meet
specific requirements of the U.S National Electrical
Code (NFPA 70); namely Article 250.2, which defines
an “effective ground fault current path,” and Article
250.4(A)(5) which defines the requirements of an
effective ground fault current path. While the key
requirement is that the grounding conductor can
never be compromised, there are two key criteria
that emphasize this:
• The grounding conductor continuity must be permanent
so safety grounding is always provided
• The grounding conductor must be low impedance
so circuit protective devices function properly.
In the U.S., the electrical standards for most boats/
yachts do not come under the U.S. National Electrical
Code (NEC), but rather under the American Boat and
Yacht Council (ABYC) standard A-28. In the most
recent revision of A-28 (published in 2008), ABYC
made provisions similar to National Electric Code
requirements, establishing a fail-safe criterion that
reflects the safety considerations taken into account
by the National Electric Code. Products that meet
or exceed the fail-safe criteria are not required to be
monitored by A-28, as the primary safety concern
has been eliminated.

On Monitoring Systems

When A-28 was initially written, it did not adopt
the previously established criteria for an effective
grounding path outlined in the NEC. As a result, early
galvanic isolators in the industry were not required to
"fail-safe". To compensate for this hazardous situation,
A-28 added a requirement for a monitoring
system, to provide an alarm if the galvanic isolator
failed open-circuit. While most manufacturers have
adopted fail-safe designs, monitored and non-monitored
systems are still available.
This is a poor substitute for a galvanic
isolator that meets failsafe requirements and
offers assured safety grounding. The very event
that would cause a galvanic isolator to fail open may
well be the event that creates the potentially hazardous
condition when grounding is lost, and which
may also damage the monitor that is to provide the
alarm. Even when the monitor alarm works properly,
a potential hazard exists until the alarm is noted and
the problem corrected.
The most reliable galvanic isolator design is one that
does not allow the safety hazard to exist.
Liability Implications of Monitored Systems
As a galvanic isolator manufacturer, we do not
believe that a lawsuit resulting from an electric shock
or electrocution that was the result of a galvanic isolator
failing open circuit, even if it meets the current
A-28 requirements by having a monitoring system,
would be defensible given the availability of fail-safe
products that eliminate this risk."


With all that said here is another explanation that has more detail about the difference between a Galvanic Isolator and an Isolation Transformer.

The following is quoted from Steve D'Antonio of PassageMaker, which also brings into the conversation the importance of a proper bonding system. Please read it all the way through and please especially note the part about Isolation Transformers.


"Most cruising boats employ some type of AC shorepower system. In fact, the newer the boat, the more complex and necessary this system is likely to be. More often than not, the most necessary consumer of shorepower is the battery charger. Even the most frugal and purist cruiser is unlikely to forgo this veritable necessity. For dockside vessels, keeping the batteries charged while the boat is unattended means having fully charged start and house batteries at all times—as well as an ample power supply for bilge pumps in the event of a hose, through-hull, or other leak.

THE SAFE SHOREPOWER SYSTEM

Once you bring AC power aboard, you must also accept responsibility for ensuring that it is safely wired. This means meeting the American Boat & Yacht Council’s specifications as described in its Standards and Technical Information Reports for Small Craft, Chapters E-2, E-4, and E-11: “Cathodic Protection,” “Lightning Protection,” and “AC & DC Electrical Systems on Boats,” respectively.

Together, these guidelines form an intricate mosaic that tries to make the mixture of electricity and seawater—an inherently unsafe combination—as safe as possible. (For the purposes of this discussion, “sea water” includes any water your boat may be floating on—salt, fresh, or brackish). One of the primary tenets of these ABYC standards is the need for bonding. Bonding is just another name for electrically connecting (a connection usually associated in some way with grounding) selected metal objects on board a boat.
These objects (sometimes referred to as masses) include such things as the engine, metallic fuel and water tanks, steering gear, metallic hardware below the waterline, spars, shrouds, davits, arches, and so on. A bonding wire is used to connect the masses. This grounding circuit is separate from the green AC safety ground circuit, but as we will see later, it is important that these two circuits be connected.

There’s no shortage of controversy where the practice of bonding is concerned. However, along with many other boatbuilders and repair yards, I subscribe to this practice for several reasons. But one reason in particular stands out: A bonded boat is less likely to electrocute one of its crew.

Aboard a properly wired vessel, if an energized AC wire—often called “hot” and typically black or red—comes in contact with one of these bonded masses, a tank or a rudder post, for instance, the electricity is safely discharged to ground and will, in theory, trip the circuit breaker as well.

On a vessel that does not follow the ABYC guidelines on bonding, the hot conductor will energize the metal mass—for example, that same tank or rudder post. If an unsuspecting crew member comes along and touches this energized mass with one hand and then touches another mass that is grounded, such as the engine block or propeller shaft, with the other hand, the resulting electrical shock across the crew member’s chest will be a frightening, if not fatal, experience.
Detractors of the practice of having a “bonded boat” argue that bonding is much more likely to result in galvanic corrosion—sometimes incorrectly referred to as electrolysis. Unfortunately, they are correct.

Galvanic corrosion, also called dissimilar-metal corrosion, occurs when two different metals—for instance, aluminum and bronze, or stainless steel and brass—remain in contact either directly or through a wire while they are immersed in an electrolyte, in this case, sea water. The rate and severity of corrosion depends on many factors: the types of metals involved, the salinity and temperature of the water, and the presence of zinc anodes, to name a few. Typically, galvanic corrosion is a relatively slow process, causing cumulative damage over the course of months, if not years.

Even if there were no solution to this dilemma—and there is—please read on, because you have a clear choice: Suffer galvanic corrosion damage or electrocute yourself or one of your crew. This should be an easy decision to make.

COMMON AC MISTAKES

In addition to the failure-to-bond problem, many vessels are plagued with other AC electrical land mines. The most notorious of these is connecting—aboard the boat—the AC neutral conductor (the white wire) and the safety grounding conductor (the green wire). Unlike in a house, aboard a boat, these two conductors should have nothing to do with each other. Rather, they must be connected only ashore.

This includes the internal wiring of appliances such as some domestic microwave ovens, coffeepots, clothes dryers, and so on. In many instances, boatbuilders, repair yards, or owners will obtain these common domestic appliances for installation aboard a vessel. These appliances must be tested, and possibly modified, to ensure safe shipboard use.

The reason for this idiosyncrasy is the potential for the transmission of current through sea water. All AC power coming aboard on the hot conductors (on a vessel equipped with 240-volt service there will be two hot conductors) must ultimately find its way back to ground. If the white and green wires are allowed to touch or are intentionally connected, ordinary current that normally returns to its source on the white wire will return to its source through the green wire as well. In a properly wired boat, the AC safety grounding circuit (the green wire) must be connected to the bonding circuit—making these two circuits essentially the same system. So current improperly flowing between the white wire and the green wire can also flow through the bonding circuit.

If a boat is wired in a way that connects the green and white wires, the current’s return could then take one, two, or all three of the following paths: through the white neutral conductor, through the green safety grounding conductor, and through the boat’s bonding circuit to underwater hardware and thence to the sea water. If high resistance develops in the neutral and/or AC safety ground conductors—this often happens when the shorepower cable contacts become corroded or wet—the sole return path for shorepower current could become the sea water.

A swimmer passing through this electrical path could be killed, even if the strength of current is not great enough to be considered lethal ashore. Sadly, this has happened on a number of occasions. Again, salt water or fresh—it doesn’t matter. In fact, studies and anecdotal evidence indicate that AC current may be more likely to be lethal in fresh water than in salt water. The reason for this is the directness of the path that current takes when it travels through fresh as opposed to salt water.

Because fresh water is less conductive than salt water, current takes a more direct path through fresh water. This more direct path results in a higher current density—that is, the amount of current present in the water at a given location. A good analogy is a lightning bolt passing through air—it’s concentrated and very direct because air (like fresh water) is a poor conductor. Greater current density means a greater difference in current potential from one location to the next, and greater potential for the current to electrocute a person or upset his or her heart rhythm, delivering a lethal shock.
In 1999, a nine-year-old boy was electrocuted as he swam in fresh water next to a marina dock. He was wearing a life jacket, and his face never touched the water. His mother jumped in to save him. As she did so, her limbs and extremities went numb. In spite of this, she was able to pull her son to the dock, where others helped pull them from the water. The ensuing investigation determined that this unfortunate tragedy occurred because of an electrical fault in a nearby unbonded boat. A melted wire allowed AC shorepower current to leak into the water around the boat and the nearby dock where the boy was swimming.

Because this was fresh water, the current had difficulty finding a path to ground, until the boy entered its path. The salinity of the human body makes it a much better conductor than fresh water. The boy’s mother was able to pass through the path of the current without being electrocuted because of her greater body weight and skin surface area, but the current was great enough to be lethal to the boy’s smaller, lighter body. Had the vessel with the offending electrical fault been bonded, it’s unlikely this tragedy would have occurred. The fault current would have passed safely ashore over the green safety grounding wire, where it would most likely have tripped the dockside circuit breaker. If no other lesson is learned from this sad tale, let it be this: Never swim in a marina or next to docks where shorepower is present.

Small amounts of AC current are sufficient to immobilize voluntary muscle reflexes, such as those needed to swim and stay afloat. Current as low as 5milliamps can cause muscle seizure. Higher current (50 milliamps for 2 seconds or 500 milliamps for just 0.2 seconds) can cause ventricular fibrillation and ultimately death. (This is probably what happened to the boy mentioned above.) Essentially, a swimmer can drown or suffer heart stoppage even in water that’s not over his or her head.

Another common AC error is severing the connection between the AC safety ground and the boat’s bonding system. Both are green wires, but of different gauges: one wired to most or all AC appliances and going ashore in the shorepower cable; the other, a series of wires aboard the boat that connects various pieces of hardware. As mentioned above, these two circuits must be connected (usually at the boat’s electrical panel) and remain at the same electrical potential at all times. Connecting the two ensures that fault current is safely conducted to the shorepower ground and that—ideally—the circuit breaker is tripped. (The boat that led to the nine-year-old’s death did not possess this connection.)

To understand the importance of this connection, consider the scenario in which a fault is created when a hot wire comes into contact with a grounded wire—usually by accident, for example, when a hot wire gets crushed between a metal tank and a support beam. Now fault current passes to the tank. If the tank is properly bonded and if the bonding circuit is connected to the AC safety grounding circuit, the current will be safely conducted to ground ashore, not through the water.

In an attempt to reduce the occurrence of corrosion, an unwitting skipper may disconnect this all-too-important connection. The reasoning is that if the underwater metal is not connected to the dock through the bonding circuit and AC safety ground, then the boat will no longer be plagued by galvanic corrosion induced by neighboring boats.

This is indeed true: Separating the bonding circuit and the AC ground circuit may reduce the likelihood of stray-current corrosion (this type of corrosion is caused by DC current that leaks into the bilgewater or the water surrounding the boat) and galvanic corrosion that travels over the shorepower green grounding wire. But disconnecting this wire will do nothing to mitigate the effects of these types of corrosion if they originate on board.

As an aside, many boat owners and even some marine professionals incorrectly assume that because it often appears that this corrosion occurs or is exacerbated when a vessel is plugged into shorepower, the culprit must be the AC power, or the marina’s AC power supply itself. In fact, nothing could be further from the truth. Galvanic corrosion and stray-current corrosion are both strictly DC phenomena. Stray current from one boat may still enter and damage another boat’s bonded underwater fittings. Although this does occur, it’s not terribly common. But nothing can prevent stray current except eliminating the bonding system, and for reasons discussed earlier, that’s not a safe option. Once this connection between AC ground and the bonding system has been disconnected, the scenario of an electrocuted crew member or swimmer pays another visit.

I once encountered the following set of circumstances. A boat owner intentionally broke the connection between the bonding and ground circuits. The boat’s microwave oven developed a short between the hot conductor and the metal enclosure, and the ground contact on the shorepower plug was heavily corroded. The scene was now set. There was no low-resistance return path to ground for the energized metal enclosure, so it remained energized. The boat was afloat. And I was working on some galley plumbing. Each time Ibrushed the microwave with my shirtsleeved arm while I was touching a bonded piece of hardware, I felt a slight tingle.

Had my sleeves had been rolled up, you might not be reading this article today. If the microwave’s safety ground and the hardware’s bonding wire had been connected, there would have been no difference in potential, and thus no possibility for electrocution, even if the shoreside ground were faulty. The moral of this story is that the AC safety ground circuit and the bonding system must always be connected, and they must remain at the same electrical potential.

THE PROBLEM

Now that we have established that your vessel should be properly wired for AC safety ground and selected onboard hardware must be bonded, you might ask why anyone would not do this. The problem is that when all of the safety precautions I have mentioned are taken, the undeniable side effect is the increased potential for galvanic corrosion when the boat is plugged into shorepower.

When you bond underwater metals and dutifully connect them to the AC shorepower safety ground, you may have unwittingly invited aboard an unwanted guest—corrosion. The circumstances are simple: You conscientiously bond your boat and inspect the zinc anodes regularly, changing them whenever they are more than 50 percent depleted. You also remain plugged into shorepower to keep the batteries up and the reefer cold, and to run an air conditioner, a microwave, a coffeemaker, or other appliances. Your slip neighbor, however, hasn’t been seen aboard his boat in months, but his boat remains plugged into shorepower to keep the fridge cold and the air conditioner running.

You have now inadvertently connected the two boats together, electrically, through the AC shorepower safety ground. Galvanic current flows from one boat to the other. When the other boat’s zinc anodes are depleted, yours take over, protecting both boats’ underwater hardware. In this case, that’s not for long. This could happen with any number of boats, potentially an entire marina.

It’s important enough to warrant repeating: Galvanic corrosion is DC (direct current) in nature. Stray current corrosion, which is different from galvanic corrosion but sometimes confused with it, requires the introduction of “leaked” voltage from, once again, a DC-positive source, such as a wire whose insulation is damaged that is immersed in bilgewater.

I have encountered many people who will argue strongly that corrosion can be caused by “hot marinas,” that is, faulty dockside AC electrical systems. This belief is usually based on a “corrosive” experience they’ve had while visiting a marina, which was, in all likelihood, caused by common DC galvanic or stray-current corrosion. But they have misidentified the source because it occurred only when the shorepower cable was connected. Personally, I have yet to find any evidence that AC current is capable of causing stray-current corrosion (other than in a laboratory or in some commercial pipelines that have been buried under high-tension power distribution cables), although DC current may be superimposed on AC circuits and consequently cause corrosion. However, faulty AC shorepower wiring is quite capable of injuring or killing people, as previously mentioned, whether swimming or not.

THE SOLUTIONS

Fortunately for cruisers using dockside shorepower, it is possible to have a safe, properly wired AC electrical system and simultaneously prevent rampant galvanic corrosion. Would it solve the problem if the damaging DC current could be prevented from sneaking aboard your boat, but the required AC safety ground current were allowed to pass unimpeded? Yes, it would, and this can be accomplished by using a device known as a galvanic isolator. Depending on the configuration, this device will prevent up to 1.2 volts from passing through the green AC shorepower safety grounding conductor, thus stopping most destructive galvanic current, which is usually less than 1 volt.

Remember, however, galvanic corrosion currents are DC in nature, so that’s all the galvanic isolator stops—again, up to 1.2 volts DC. It will not prevent AC voltages/currents from passing through it, so the safety ground remains intact, in accordance with ABYC standards. (Any galvanic isolator you purchase or have installed should comply with the latest and most stringent ABYC standard: section A-28 of the Standards and Technical Information Reports for Small Craft. If your vessel is already equipped with a galvanic isolator and it does not meet this standard, consider upgrading it with a compliant model.)

If the galvanic isolator solved the shorepower-induced corrosion problem completely, I could end my discussion here. Unfortunately, this is not the case. The Achilles heel of the galvanic isolator is twofold. Its primary weakness is that when it is subject to high DC fault voltage (this may be as little as the previously mentioned 1.2 volts), the isolator becomes essentially transparent, conducting any current that cares to pass through it. This effectively nullifies the corrosion firewall effect of the galvanic isolator. Unfortunately, unless your boat’s electrical system is equipped with a monitoring device, you may never know the galvanic isolator is not working. For that very reason, the latest ABYC standard calls for incorporating a monitoring device into every galvanic isolator.

The galvanic isolator’s other shortcoming is its inability to prevent other shorepower-induced faults, the most notorious being reversed polarity. If this situation exists, the galvanic isolator will have no effect on it. Undoubtedly, it is better to have a galvanic isolator—one must be installed on each shorepower inlet or circuit—than not. However, the prudent cruiser must be aware of its limitations.

The ultimate solution for most of these problems is the isolation transformer. Once installed, the isolation transformer acts much like its own power supply, similar to a generator or an inverter, or a utility company, for that matter. All voltage produced by the isolation transformer seeks a return to its origin, not just any ground. The importance of this feature cannot be overemphasized. Shorepower voltage, once it passes through the isolation transformer, will return only to that isolation transformer, through either the white neutral conductor or the green safety grounding conductor, whether by design or fault. Voltage that now emanates from the isolation transformer will never travel through sea water to seek a path to ground. This protects swimmers. Damaging galvanic voltages that normally would be allowed to come aboard via the green safety grounding conductor in the shorepower cable are also thwarted, because there is no longer any direct connection to shoreside grounds. This is where the isolation transformer and the galvanic isolator diverge. Where the galvanic isolator attempts to block DC current from coming aboard, like the walls around a medieval fortress, the isolation transformer severs this connection altogether, much like digging a moat around the same fort, filling it with water and crocodiles, and pulling up the drawbridge.

The isolation transformer achieves all of this through the principle of magnetic inductance. Here’s how it works. Shorepower voltage travels from the dock, through the shorepower cable or cables, and onto the boat’s shorepower inlet. As is the case for the galvanic isolator, one transformer is required for each shorepower inlet. But instead of allowing current to go from there to the shorepower circuit breaker panel, the isolation transformer interrupts the current before it can reach the circuit breaker. The incoming AC power travels through the primary or input winding of the transformer and back to shore. That’s as close as the dockside shorepower ever gets to the boat’s electrical system. Electricity is induced on the transformer’s secondary or boat side winding magnetically. There is no direct connection. This arrangement eliminates the possibility of reverse polarity and of unintentionally creating the potential for a swimmer either drowning—because the electricity paralyzes his or her voluntary muscle reflexes—or, if the current is strong, being electrocuted. (It’s telling that vessels equipped with isolation transformers are exempt from ABYC’s reverse-polarity indicator requirement.)

Additionally, much like the power sources mentioned above, the onboard AC green safety grounding conductor now originates at the secondary winding of the isolation transformer. As a result, shoreside grounds and the boat’s ground have nothing in common. This reduces the potential for foreign stray-current corrosion. Stray-current corrosion, which originates domestically—that is, aboard your own boat—is still potentially destructive and not prevented by the isolation transformer or any other device or practice except good wiring procedures. With the installation of the isolation transformer, all onboard bonding, DC grounds, and AC safety grounds remain unchanged, provided they previously met the ABYC standards mentioned at the beginning of this article.

The primary drawbacks of the isolation transformer are its size and weight. The average 30-amp unit may measure roughly a foot square and weigh 60 pounds. Although such a unit is not impossible to accommodate, all space aboard cruising boats is precious. Additionally, an isolation transformer has to be properly ventilated.

When shopping for a unit, the primary prerequisites are a marine UL listing (most isolation transformers are UL listed, but not all carry the “marine” prefix), full adherence to ABYC’s standards for isolation transformers, and a shield between the primary and secondary windings that is able to carry the full current rating of the unit in the event of a short circuit. The final requirement is that there must be no connection between the isolation transformer’s windings and shoreside ground. Beyond that, there are several case and shield grounding configurations and options. Some units are even capable of boosting low dockside voltage.

One point worthy of mention: Isolation transformers and polarization transformers are not the same thing. The latter only ensure correct onboard polarity in the event of a dockside fault. They will do little if anything to prevent corrosion, and the return path of the current to shoreside ground remains unchanged. If you have a polarization transformer, you are protected only from reverse-polarity scenarios—dangerous though they are—not from shore-induced corrosion or the possibility that you will electrocute a swimmer.

The isolator and transformer are not mutually exclusive systems. Some boats use both—the galvanic isolator supplements the case ground of an isolation transformer—but this is a belt-and-suspenders approach. In most cases, the economical approach is to use the galvanic isolator, and the all-inclusive approach, which affords the greatest corrosion prevention and some protection against electrocution, is to use the isolation transformer. Given the choice, I’d opt for the latter, but it’s not practical for every boat because of its size, weight, and expense. At a minimum, every boat that uses shorepower should have a galvanic isolator.

Only a small number of isolation transformer manufacturers produce units appropriate for the recreational cruising vessel, specifically, single-phase 120/240VAC, 30/50 amp service. Whichever product you may use, ensure that the installation instructions are followed to the letter. (If the isolation transformer is not installed property, you won’t get the benefits of this system and will have wasted your money.) Unless you are trained and experienced, AC shore power wiring should be left to the pros—and preferably to an ABYC-certified marine electrician."

Hopefully this article will answer all your questions, because I am definitely not going to write any more on this. I will not respond to any further inquiries. I used to be paid for this and I retired 8 years ago.

Sincerely backing out,
Lou

[HankOnthewater]

Thank you Sailerlou for the very good contribution above!

[Ahmet Erkan]

Sailorlou,
No wonder the boaters are so confused. We asked what time it is and got told how to build a watch. Thank you anyway.
I must admit, most of the verbiage is accurate and obviously written by and/or recommended by people who have a high level of expertise in marine power systems but very little of the verbiage is relevant to our discussion.
Once again, the subject of our discussion :
Is the safety of nearby swimmers compromised when the connection between the shore power grounding conductor and ship’s underwater metals is disconnected.
Are you saying nearby swimmers can be just as safe when the Shore Power Grounding Conductor is disconnected from the underwater metals of a boat if an isolation transformer is installed?
I am saying the swimmers nearby would be much safer if the shore power grounding conductor is left alone connected to the ship's hull ground through a proper galvanic isolator with a proper monitor.
I am further saying in this post that people who sell the sailors a $6 rectifier for $600 are crooks that EE sailors in this community should expose. The products Isolation Transformer, and Galvanic Isolator mentioned anywhere in this discussion means properly designed and manufactured products. (ie: The isolation transformers have side by side coils, twin bobbins, shields, physically separate primary and secondary windings, class H insulation, at least -60dB common mode noise attenuation, whatever, Galvanic Isolators with proper rectifiers, capacitors, external monitors, warning lights etc.)
All products should come with either real schematics or one line diagrams and not insult the boaters intelligence with wiring diagrams designed for the stupid with wires that terminate at some terminal block and the user has no idea where the cable is going inside the cabinet.

Lou, we are still not finished. You have not told us how your isolation transformer protects the swimmer when the shore power hot conductor shorts to the hull ground and the leakage current is not enough to trip the shore power CB or if the CB is a regular CB and not an ELCI or GFCI?
(ie: How would have your isolation transformer protected the sad fatality of the nine year old boy in the fresh water marina?)
By the way the article you forwarded did not describe what exactly the root cause of the failure was that resulted in the tragic accident. “Melted wire allowed shore power current to leak into the water” Duh. What shorted to what? What should have been connected to what?
Regards.
Ahmet

[ronstory]

SailorLou, Great background and overall summary! pulling that info together into one post is most appreciated

[Sailorlou]

Originally Posted by Ahmet Erkan

Sailorlou,
No wonder the boaters are so confused. We asked what time it is and got told how to build a watch. Thank you anyway.
I must admit, most of the verbiage is accurate and obviously written by and/or recommended by people who have a high level of expertise in marine power systems but very little of the verbiage is relevant to our discussion.
Once again, the subject of our discussion :
Is the safety of nearby swimmers compromised when the connection between the shore power grounding conductor and ship’s underwater metals is disconnected.
Are you saying nearby swimmers can be just as safe when the Shore Power Grounding Conductor is disconnected from the underwater metals of a boat if an isolation transformer is installed?
I am saying the swimmers nearby would be much safer if the shore power grounding conductor is left alone connected to the ship's hull ground through a proper galvanic isolator with a proper monitor.
I am further saying in this post that people who sell the sailors a $6 rectifier for $600 are crooks that EE sailors in this community should expose. The products Isolation Transformer, and Galvanic Isolator mentioned anywhere in this discussion means properly designed and manufactured products. (ie: The isolation transformers have side by side coils, twin bobbins, shields, physically separate primary and secondary windings, class H insulation, at least -60dB common mode noise attenuation, whatever, Galvanic Isolators with proper rectifiers, capacitors, external monitors, warning lights etc.)
All products should come with either real schematics or one line diagrams and not insult the boaters intelligence with wiring diagrams designed for the stupid with wires that terminate at some terminal block and the user has no idea where the cable is going inside the cabinet.

Lou, we are still not finished. You have not told us how your isolation transformer protects the swimmer when the shore power hot conductor shorts to the hull ground and the leakage current is not enough to trip the shore power CB or if the CB is a regular CB and not an ELCI or GFCI?
(ie: How would have your isolation transformer protected the sad fatality of the nine year old boy in the fresh water marina?)
By the way the article you forwarded did not describe what exactly the root cause of the failure was that resulted in the tragic accident. “Melted wire allowed shore power current to leak into the water” Duh. What shorted to what? What should have been connected to what?
Regards.
Ahmet

Ahmet,

In answer to your question,

"Are you saying nearby swimmers can be just as safe when the Shore Power Grounding Conductor is disconnected from the underwater metals of a boat if an isolation transformer is installed?"

The simple answer is "Yes". I'll re-state what is in the information I put in the last post. If you had read it thoroughly you would have seen the answer to your question.

The output side of an Isolation transformer becomes the source and the return to ground goes back to the source, which is the Isolation Transformer, not the shore ground. The electricity will not enter the water in a properly wired and maintained electrical system utilizing an Isolation Transformer.

That is not to say a boat nearby will be safe. The best approach is simply to stay out of the water in a marina environment. But, if every boat had an Isolation Transformer it would be a lot safer. A better way would be to place an Isolation Transformer at each source pedestal on the dock. Several years ago California actually introduced legislation to try to get a law passed requiring this at marinas, but unfortunately it didn't get passed.

You seem to like to argue for the sake of argument. Why don't you take the classes from ABYC and become a certified ABYC Marine Electrician. Maybe that will convince you. Obviously I can't.

The boy mentioned that died, in the article I quoted, was Kenvin Ritz's son. Why don't you give Kevin a call at ABYC, maybe he will be able to convince you. But probably not. There is no 100% solution.

There will always be a point of failure in any system that can be designed. The point of failure you keep bringing up is where the hot lead from the shore power feed shorts to the bonding system ahead of the transformer. This is a possible failure point. Also, you can have a single wire failure point on a Galvanic Isolator, namely, what if the ground wire in the feed from the shore source opens? Your return to ground is now the water.
I could, like you, keep pointing out possible points of failure in any design. There is no system that cannot fail. An Isolation Transformer is the best available solution.

Kevin Ritz's number and email is - (503)543-9777 / kevintritz@gmail.com
or you can call Capt. David Rifkin (USN, Ret) at (904)382-7868 / qualitymarinesvcs@comcast.net.

Kevin Ritz and Capt. David Rifkin established a web site that is dedicated to ESDP (Electric Shock Drowning Prevention). There is a video on the web site where Kevin explains what happened to his son.
Here is the link - https://www.electricshockdrowning.org/.

You can also go to Mike Holt Enterprises for some of the best classes in the industry. Here is a link to Mike's web site - https://www.mikeholt.com/index.php.

[Pelagic]

Sailorlou
I found this quite appropriate
[emoji4]

https://gloria.tv/video/bDZgrE7Djbwz4wWxxFwDwBhfK

[Sailorlou]

Originally Posted by Pelagic

Sailorlou
I found this quite appropriate
[emoji4]

https://gloria.tv/video/bDZgrE7Djbwz4wWxxFwDwBhfK

Pelagic,

I actually watched the cartoon video.
Although I'm not a religious person, I was raised in a very religious family and am well aware of the "Patience of Job".
I would ask you one question. Are you saying, 1) I need to have more patience. 2) My patience is being tested. or 3) You think I have a goodly amount of patience?

I'd like to think that both 2 and 3 are true.

Either way thanks for your comment. It gave me a good laugh.
Lou

[Pelagic]

Originally Posted by Sailorlou

Pelagic,

I would ask you one question. Are you saying, 1) I need to have more patience. 2) My patience is being tested. or 3) You think I have a goodly amount of patience?

I'd like to think that both 2 and 3 are true.

Either way thanks for your comment. It gave me a good laugh. [emoji2]
Lou

It was meant to lighten the mood and yes 2&3.[emoji6]

[Neptune's Gear]

Sailorlou, great posts, and I’m in total agreement. Here in NZ, the US rules and cable colours are different, but electricity is electricity. I tell my customers that anyone who has shore power without at least a failsafe galvanic isolator, preferably with monitor, is a fool. That protection is stage 1. Best is an isolation transformer.... our rules here actually require neither, which is scary.

[Oceansailor]

Could we not agree that a galvanic isolator only protects the boat.

An isolation transformer protects boat even better and in addition also protects people?

[Ahmet Erkan]

Originally Posted by Oceansailor

Could we not agree that a galvanic isolator only protects the boat.

An isolation transformer protects boat even better and in addition also protects people?

Dear Oceansailor,
The short answer is, a properly installed isolation transformer on board a vessel does not protect the boat. The improper advice given by “experts” on this forum to disconnect the shore power ground from the hull ground (because the transformer through some magic makes everything safe) actually will protect the boat but at the price of endangering the swimmers or divers near the boat.

1. A fail safe galvanic isolator will always protect the swimmers and with a properly designed power system monitor it will also guarantee the boat is protected as well.
2. A dock mounted isolation transformer with an onboard properly designed power system monitor will also protect the boat and protect the swimmers. NOTE: The shorepower grounding conductor is still required to be brought onboard for the power system monitor to test and verify isolation and that the system has no single point failures for the swimmers protection.

Fellow Ocean Sailor,
I have defended items 1 and 2 above based on sound electrical principles but I have also been raised with values from a culture which considers bragging, chest beating etc as inferior forms of behavior. Therefore, if you are not a marine power systems expert and if you are going to believe me only if I have at least the same academic credentials and work experience as the other experts on this forum, feel free to contact me privately.
Lastly, experts in this forum should not recommend improper wiring of isolation transformers and ABYC should consider phasing out the older wiring diagrams in E11 which show no connection between the shore power grounding conductor and the underwater metals of the vessel. In fact if I am not mistaken the current technical committee at ABYC state they are not responsible for some of the figures in the documents that were introduced by the original technical management. Also ABYC states they are not the law, but recommendations and guidelines. Excellent and prudent guidelines I must admit except for a few legacy figures that their time has passed and they should be revised out.
Cheers mate
Ahmet (ahmet_erkan@sss-nc.com)