Onboard Isolation Transformer vs Safety

[DotDun]

An isolation transformer eliminates stray current/voltage issues from affecting your boat and eliminates the need for reverse polarity monitoring.

[DotDun]

Originally Posted by Ahmet Erkan

dfeltsent,
Here are a few thoughts about single point failures with isolation transformers and galvanic isolators.
A single point failure is not desirable for obvious reasons. There are also cases that a single point failure cannot be eliminated but the risk of occurrence is minimized by various means. For example a small airplane cannot have a redundant second engine (because it would be too heavy, too expensive etc) but a single engine airplane has a special engine with dual redundant spark plugs, magnetos, fuel tanks etc. Not only these dual redundant systems are built in but the pilot verifies each redundant system is operational prior to flight.
Lets look at an isolation transformer installed at the dock. The neutral of the transformer is not grounded.

Then, it's not neutral, it's L2. Plus this goes against NEC & ABYC codes.

Originally Posted by Ahmet Erkan

The hot, neutral and ground conductors are brought into the boat via the shore power cable. The underwater metals of the boat are electrically floating. (as well as floating on the water)
Now the system does not have single point failures. You do not have to connect the shore grounding conductor to the underwater metal of the boat. If any hot conductor shorts to the hull the diver will not get electrocuted because there is no return path to ground from the hot conductor.
The only way the diver can get electrocuted is if two failures occur simultaneously. For example if the hot conductor shorted to the hull and the neutral conductor shorted to the ground. A caveat with the systems that do not have single point failures is an effective warning system must exist when a failure has occurred.
So please do not think that an isolation transformer on board is going to make your corrosion problems go away

Statements like this makes one believe you don't understand galvanic corrosion.

Severing the shorepower ground connection from boat ground solves ALL galvanic corrosion issues caused by neighboring boats and poorly wired marina electrical systems. An isolation transformer alleviates the need for shorepower ground.

Originally Posted by Ahmet Erkan

and provide safety just like it does for the patient at the hospital.
People who have disconnected the shore power grounding conductor from the underwater metals of their boats because they have been misguided by the manufacturers of isolation transformers. Get a galvanic isolator. Your boat is a disaster waiting to happen,

Originally Posted by Ahmet Erkan

especially in a fresh water marina.

The failures you describe are simply figments of your imagination. You need to provide evidence that anything like you are describing has ever happened. The sky could fall tomorrow also, what is your plan for that??

[Ahmet Erkan]

DotDun
NEC requires the secondary of a pole transformer to be brought to a house and the Neutral conductor (center tap of an isolated 240V winding) to be bonded to the chassis of the distribution panel after the wires enter the house. What I am recommending is compliant with the NEC in all respects. The wiring instructions from the “marine isolation transformer” manufacturer (and your recommendation) is non-compliant with the NEC while the boat is in the water (read this as not safe), and a jumper is recommended when the boat is in a drydock to make it compliant with the NEC to protect the yard workers.
Listen very carefully now. If the neutral conductor is grounded ashore before the power is brought into the boat it will not be possible to test the isolation transformer and if the hot conductor shorts to the boat ground, this would be a "single point failure" which will electrocute the diver. I am trying to explain a method to break the connection between the shore ground and the boat ground in a safe manner and you are defending a clearly unsafe wiring method that is also non-compliant with the NEC. Furthermore you are being rude with your “sky falling” sarcasm and asking me what my plan might be.
Ahmet

[DotDun]

Originally Posted by Ahmet Erkan

DotDun
NEC requires the secondary of a pole transformer to be brought to a house and the Neutral conductor (center tap of an isolated 240V winding) to be bonded to the chassis of the distribution panel after the wires enter the house. What I am recommending is compliant with the NEC in all respects. The wiring instructions from the “marine isolation transformer” manufacturer (and your recommendation) is non-compliant with the NEC while the boat is in the water (read this as not safe), and a jumper is recommended when the boat is in a drydock to make it compliant with the NEC to protect the yard workers.
Listen very carefully now. If the neutral conductor is grounded ashore before the power is brought into the boat it will not be possible to test the isolation transformer and if the hot conductor shorts to the boat ground, this would be a "single point failure" which will electrocute the diver. I am trying to explain a method to break the connection between the shore ground and the boat ground in a safe manner and you are defending a clearly unsafe wiring method that is also non-compliant with the NEC. Furthermore you are being rude with your “sky falling” sarcasm and asking me what my plan might be.
Ahmet

1) ABYC extends/modifies NEC due to the special application of boats in the water (which NEC clearly doesn't understand).
2) An isolation transformer is identical to a pole transformer from a neutral grounding perspective. Just like the pole transformer an isolation transformer is a new power source, hence you ground either the center tap of the secondary in a split-phase application or one side in a single phase application. The now neutral is then bonded (per ABYC) to boat ground. Never should you bond shorepower ground to boat ground when using an isolation transformer, this is supported by ABYC.
3) As mentioned previously, your failure mode (as remote as it may be) can be handled by putting an ELCI between the shorepower inlet and the isolation transformer primary. I did this to help protect the transformer in a static build-up (lightning side flash) situation (arcing between primary and screen). Whether the ELCI will trip in time to save the coil remains to be seen. I also installed MOVs between shorepower L1 and shorepower ground and shorepower L2 and shorepower ground hoping for more protection.

Please provide evidence that your use case has ever happened where the result was a swimmer/diver got hurt.

[dfelsent]

Ahmet —
I appreciate your concerns but.

NEC 90.2 B 1 specifically excludes boats.

Please recognize that there are very specific applications that are covered by various standards. The standards are a compendium of best practices, not a rigid one size fits all set of requirements for all situations.

And before you take offense at anyone else’s tone please recall that you not only misspelled my use name but you said “Your boat is a disaster waiting to happen, especially in a fresh water marina. ” without knowing anything about my boat, it’s installations, or its use. And I did not and do not take offense at that.

[Ahmet Erkan]

Originally Posted by dfelsent

Ahmet —
I appreciate your concerns but.

NEC 90.2 B 1 specifically excludes boats.

Please recognize that there are very specific applications that are covered by various standards. The standards are a compendium of best practices, not a rigid one size fits all set of requirements for all situations.

And before you take offense at anyone else’s tone please recall that you not only misspelled my use name but you said “Your boat is a disaster waiting to happen, especially in a fresh water marina. ” without knowing anything about my boat, it’s installations, or its use. And I did not and do not take offense at that.

I apologize for misspelling your username dfelsent.

The reference to NEC was made because someone said it would be in violation of NEC if the isolation transformer was installed at the pedestal (ie: ashore) with its Neutral not bonded to shore power ground. That person was mistaken but NEC would be applicable in a shore pedestal mounted isolation transformer.

if I am not mistaken you said you will use an isolation transformer and no galvanic isolator. So in my mind yes that will make your boat a disaster waiting to happen, especially in fresh water.
I recommend you connect the shore power grounding conductor to the underwater metals of your boat through a galvanic isolator.

After installing the galvanic isolator you can go ahead and follow the manufacturer's instructions to wire your isolation transformer and the diver will not be subjected to a single point failure and also adding a jumper to the isolation transformer to make your boat safe for the yard workers will not be necessary, because the yard workers will be just as safe from electrocution as the divers and/or any swimmers.

[Ahmet Erkan]

Originally Posted by DotDun

1) ABYC extends/modifies NEC due to the special application of boats in the water (which NEC clearly doesn't understand).
2) An isolation transformer is identical to a pole transformer from a neutral grounding perspective. Just like the pole transformer an isolation transformer is a new power source, hence you ground either the center tap of the secondary in a split-phase application or one side in a single phase application. The now neutral is then bonded (per ABYC) to boat ground. Never should you bond shorepower ground to boat ground when using an isolation transformer, this is supported by ABYC.
3) As mentioned previously, your failure mode (as remote as it may be) can be handled by putting an ELCI between the shorepower inlet and the isolation transformer primary. I did this to help protect the transformer in a static build-up (lightning side flash) situation (arcing between primary and screen). Whether the ELCI will trip in time to save the coil remains to be seen. I also installed MOVs between shorepower L1 and shorepower ground and shorepower L2 and shorepower ground hoping for more protection.

Please provide evidence that your use case has ever happened where the result was a swimmer/diver got hurt.

DotDun,
Not sure what evidence you need from me. Hot conductor shorting to chassis (aka a ground fault) is probably the most common failure mode in equipment, it probably happens millions of times every year. This is exactly why all safety agencies require incoming power source grounding conductor to be bonded to the chassis. The "marine isolation transformer" manufacturer's instructions state NOT to bond the shore power grounding conductor to the chassis of the transformer but bond the underwater metal of the boat to the chassis of the transformer. So if the hot wire from shore power entering the transformer shorts to the chassis the diver will be toast.
Do a google search with keywords "fresh water electrocution drownings" and you will find hundreds of divers/swimmers that are not just hurt but dead.
Here is a famous 2014 presentation.
https://www.nfpa.org/~/media/1566859...44036C59F4.pdf

[Paul Elliott]

Originally Posted by Ahmet Erkan

Here is a famous 2014 presentation.
https://www.nfpa.org/~/media/1566859...44036C59F4.pdf

You do realize that not one of the electrocutions in that presentation involved an isolation transformer, don't you? And that an isolation transformer (with case connected to boat ground) would have prevented many of the boat-related electrocutions?

[DotDun]

Originally Posted by Ahmet Erkan

DotDun,
Not sure what evidence you need from me.

I'll ask again. Provide evidence that the fault you describe with an isolation transformer installed in a boat has: 1) actually happened; 2) caused a diver/swimmer harm.

It's your claim, I'm simply asking for you to support it.

Originally Posted by Ahmet Erkan

Hot conductor shorting to chassis (aka a ground fault) is probably the most common failure mode in equipment, it probably happens millions of times every year.

This is simply absurd! The most common? Really?

Making such a general statement then applying it to marine isolation transformers is another level of absurdity. It certainly doesn't help with your credibility that you know what you are talking about.

Originally Posted by Ahmet Erkan

This is exactly why all safety agencies require incoming power source grounding conductor to be bonded to the chassis. The "marine isolation transformer" manufacturer's instructions state NOT to bond the shore power grounding conductor to the chassis of the transformer but bond the underwater metal of the boat to the chassis of the transformer. So if the hot wire from shore power entering the transformer shorts to the chassis the diver will be toast.

It's now obvious you have little knowledge of recreational boat wiring standards, galvanic corrosion, and stray voltage. You attack the manufacturers who are simply following ABYC specs. Good luck convincing ABYC!

Originally Posted by Ahmet Erkan

Do a google search with keywords "fresh water electrocution drownings" and you will find hundreds of divers/swimmers that are not just hurt but dead.
Here is a famous 2014 presentation.
https://www.nfpa.org/~/media/1566859...44036C59F4.pdf

As has already been pointed out, of the 109 cases in your reference, ZERO were due to an isolation transformer.

For readers trying to learn from this thread, when installing your isolation transformer, please follow ABYC specs, not Ahmet specs.

[transmitterdan]

Ahmet,

The failure modes (loose connections, etc.) you are worried about can happen to a galvanic isolator too. Isolation transformers are a great solution and much safer than galvanic isolators because the shore power systems around the world are basically terrible and often the ground conductor isn't connected to anything.
So the arguments you are making are not rational in my view. Many experts have weighed the risks and developed standards which manufacturers in Europe and US follow. If you think they are wrong take it up with the standards bodies. Causing fear, uncertainty and doubt about electricity in an Internet forum can get someone killed too.
Anyone reading this thread should always follow the manufacturer's installation instructions. Don't listen to everything you hear on the Internet. Some of it is bad information.

[Ahmet Erkan]

Originally Posted by Paul Elliott

You do realize that not one of the electrocutions in that presentation involved an isolation transformer, don't you? And that an isolation transformer (with case connected to boat ground) would have prevented many of the boat-related electrocutions?

Yes sir I understand, and agree with half of what you have said. Let me explain what I think I understood and maybe you can explain what I may not have understood.
Captain Rifkin's presentation (page 14 at the end) states in 1989 OSDH inspected 116 commercial docks, found 96% not in compliance with NEC and the most common failure was observed as "open ground". An open ground failure that has not been detected will reduce the system safety status and make it susceptible to a single point failure. (ie: Reduced to the same lower state as when the shore power grounding conductor is deliberately disconnected from the underwater metals per misguided instructions) Again, the shore power hot conductor shorting to the transformer chassis will cause a voltage gradient in the freshwater marina and cause an electrocution. Doing justice to the transformer, when the shore power grounding conductor has failed open and a ground fault failure occurring at the secondary of the transformer will not harm the diver.
What I can't get my head around is how connecting the chassis of the transformer to underwater metals makes the system any safer. I am requesting an explanation for that part of your response.
Thank you
Ahmet

[transmitterdan]

Ahmet,

If the shore power ground is disconnected how is a galvanic isolator going to help? Without a shore ground path a galvanic isolator is impotent.

[transmitterdan]

Ahmet,

If you are and electrical expert please draw the schematic of a boat with an isolation transformer connected to shore power. Then look at all possible faults. You will find that there is no possibility for shore side “hot” to reach the water with a properly designed and installed isolation transformer.

For an isolation transformer to function it has to “isolate” shore power from the boat and water. By connecting shore ground to the boat and underwater metal then it would no longer be isolated.

Draw the circuit and you will easily answer your original question.

[bletso]

Here is a typical ISO wiring.

[Paul Elliott]

Originally Posted by transmitterdan

Ahmet,

If you are and electrical expert please draw the schematic of a boat with an isolation transformer connected to shore power. Then look at all possible faults. You will find that there is no possibility for shore side “hot” to reach the water with a properly designed and installed isolation transformer.

The one possible fault that Ahmet is describing is where a shore power hot lead shorts as it passes through the grounded (to boat ground) isolation transformer case, possibly due to degraded insulation, or perhaps a screw terminal coming loose. This fault will indeed create an electrocution hazard.

But the anecdotal evidence suggests that this is an *extremely* *unlikely* fault, and as far as we can tell this has never actually happened.

So why is the isolation transformer put inside a metal box? I don't know, and we've heard that some transformers have a non-conductive enclosure.

And why should the metal transformer case be tied to boat ground? I suppose we would rather connect to ground a metal box that has high-voltage wires inside, and using boat-ground makes better sense from a boat-safety standpoint. Leaving it floating makes it vulnerable to capacitive coupling from the transformer -- a minor shock hazard.

Regardless, I am far from convinced that this potential single-point failure is reason to connect the transformer case to shorepower-ground in addition to boat-ground, since doing so would require adding a diode galvanic isolator, with it's own various failure modes (some of which are just as bad as the one that Ahmet is worried about). And there are definitely safety benefits to the isolation transformer, especially given the poor condition of many shorepower connections. As I mentioned previously, many of the electrocutions described in that paper Ahmet gave us the link for would have been prevented had there been a properly-installed isolation transformer.