Onboard Isolation Transformer vs Safety

[Ahmet Erkan]

Originally Posted by DotDun

If diver safety is the goal, why a GI vs straight connection?

#5 - need to define the failure, not all failures are dangerous to a diver.

GI is introduced to prevent galvanic corrosion while not disconnecting the shore power ground from the hull ground.
Point taken about #5 I have added all relevant failure modes.

Here is the latest points 1 through 6 about galvanic isolators and I have added #7 to cover my claim about on board isolation transformers.
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1. The GI is installed between the shore power ground and the hull ground (hull ground=underwater metals of the boat)
2. The divers typically work between the shore power ground and the hull ground.
3. Therefore the GI is connected in parallel with the diver.
4. The fail safe GI has only a few volts across it and the diver cannot get electrocuted with a few volts across his/her body.
5. CONCLUSION : The GI protects the diver from electrocution during an electrical failure. The electrical failure could be any ungrounded AC conductor on board and/or inside an on board appliance making contact with the hull ground. (aka a typical and common ground fault failure)
6. CATCH : As Captain Rifkin reported in his presentation a common failure at marinas is open ground. As CharliJ pointed out the GI monitor needs to verify that the shore power grounding conductor is indeed connected to the shore power ground.
7. ON BOARD ISOLATION TRANSFORMERS : Some manufacturers claim an onboard marine grade isolation transformer can completely isolate the shore power and the shore power grounding conductor from the hull ground and a galvanic isolator can be removed while safety for a diver working under the boat is still maintained. References are made to the ABYC standard E11 diagrams #6 and #7 to validate this claim.
At least one electrical engineer claimed on a CF forum that the said diagrams #6 and #7 used to wire a boat AC power system are not safe for divers or swimmers around this boat when the boat is connected to shore power, especially in a fresh water marina. The said electrical engineer also claims that an onboard isolation transformer and wiring cannot be modified enough to provide an equivalent level of safety as compared to a galvanic isolator to protect a diver or swimmer such that the galvanic isolator can be removed and the shore power grounding conductor can be left disconnected from the underwater metals of a boat.
Ahmet

[transmitterdan]

Ahmet,

Your claims of lack of safety regarding the isolation transformer installed per ABYC recommendations require specific examples of a failure mode. It also requires statistical analysis as to how common is that mode. For example, failure of the shore power safety earth wire is known to be very common. Likewise, mis-wiring of shore pedestals is also common. An isolation transformer blocks DC and simultaneously dramatically reduces shock risk to swimmers when the shore earth wire is absent or has high resistance or has been mid-wired.

We should not be confusing people by claiming that isolation transformers are less safe than a GI which provides no safety isolation whatsoever.

For lay people reading this thread, an isolation transformer provides a boat with the same kind of “double insulation” that many hand tools have. This extra insulation significantly reduces risk of shock. An isolation transformer also eliminates the need for a galvanic isolator (GI) altogether. The main drawback of an isolation transformer is size and weight. But they significantly improve safety for swimmers.

And no one should swim around boats in a marina. There are other ways to get shocked having nothing to do with the boats. The docks themselves can be a shock hazard.

Divers cleaning boats have special training and they should be able to assess risk of shock. They don’t need any warning signs because they are well aware of the problems of electricity around water.

[Ahmet Erkan]

Originally Posted by ramblinrod

400 Volts?!?!? Wholly light up the occupants and burn down the boat Batman. If we are truly trying to prevent electrocution, higher voltage is the wrong direction.

ramblinrod,
The 400Vdc was offered in response as a courteous move to the somewhat cavalier comments from a NZ sailor who said he did not need AC on board so I gave him a 300Adc battery charging current with a smaller shore power cord but he did not like that either.
Again, the 400Vdc output that is regulated and power factor corrected is the standard front end platform for power supplies. It is an industry standard and at times manufactured at 20,000 pieces per week. 120Vac and 240Vac on your shore power cable deserves the same respect as 400Vdc and if the system designer is not capable of designing for safety both can become equally lethal.
The scare tactics are not necessary, the users may not be subject matter experts and they are quite intelligent to understand explanations using common sense.
Having said all of the above, the 400Vdc is not the subject of this discussion, I regret responding to the NZ sailor's post and mentioning it.
Of course now the 400Vdc is going to be used by opportunists to invalidate the warning not to disconnect the shore power grounding conductor from the underwater metals. (through the GI)

Rod, if you have to hit under the belt no problem, bring it on anyway. My posts are based on solid laws of physics.

Ahmet :-)

[Ahmet Erkan]

Originally Posted by transmitterdan

Ahmet,

Your claims of lack of safety regarding the isolation transformer installed per ABYC recommendations require specific examples of a failure mode. It also requires statistical analysis as to how common is that mode. For example, failure of the shore power safety earth wire is known to be very common. Likewise, mis-wiring of shore pedestals is also common. An isolation transformer blocks DC and simultaneously dramatically reduces shock risk to swimmers when the shore earth wire is absent or has high resistance or has been mid-wired.

We should not be confusing people by claiming that isolation transformers are less safe than a GI which provides no safety isolation whatsoever.

For lay people reading this thread, an isolation transformer provides a boat with the same kind of “double insulation” that many hand tools have. This extra insulation significantly reduces risk of shock. An isolation transformer also eliminates the need for a galvanic isolator (GI) altogether. The main drawback of an isolation transformer is size and weight. But they significantly improve safety for swimmers.

And no one should swim around boats in a marina. There are other ways to get shocked having nothing to do with the boats. The docks themselves can be a shock hazard.

Divers cleaning boats have special training and they should be able to assess risk of shock. They don’t need any warning signs because they are well aware of the problems of electricity around water.

transmitterdan,
The isolation transformer secondary that is disconnected from the ground typically floats at about half the secondary voltage due to capacitive coupling. At 120Vac the neutral of the secondary will float at about 60Vac. The Europeans use 240V so the secondary neutral will float at about 120Vac. Plus the no shield over the secondary makes the capacitive coupling at a lower impedance so a finite (ie: few mA) leakage current at 120Vac could be observed at the propeller and shaft of a yacht with an isolation transformer in drydock in Europe. This why Victron instructs the user of their isolation transformer to re-connect the shore power ground to the underwater metals when the ship is on the hard.
Now, if the isolation transformer without the jumper is not safe enough for workers when the boat is in fresh air, why should it be safe for the workers in fresh water?
USE A GALVANIC ISOLATOR.
Ahmet

[transmitterdan]

Ahmet,

There is no issue in water because the tiny displacement current is dispersed in the water. You are tilting at a windmill.

[Ahmet Erkan]

Originally Posted by CharlieJ

BEGIN RANT
The marine industry is a very, very small slice of the industrial pie. Most of the products that we use come from home (solar panels), automotive (alternators), trucking (alternators, electric fuel pumps) or the RV (waste pumps) industries. That is why we are stuck with 12 volt systems, for instance.

I point this out so that everybody understands that the companies that make the products that we use are not really interested in investing R & D funds for such a small industry slice. Companies like SmartPlug have taken the plunge and developed a better alternative to the original twist-lock but it has NOT been an easy road for them. (Full disclosure: I am one of the original SmartPlug Dealers)

The marina segment of our industry is notoriously cheap. As RC Collins says, when something fails on a pedestal, the marina management sends Daryl and Daryl down to straighten it out. They replace the shore power outlet and manage to reverse polarity, not tighten the fasteners holding the conductors in the outlet, forget to connect the safety ground, etc. The requirement for an annual check of the grounding system in a marina has been in NFPA 70 (NEC) for many, many years. I know of no marina in my area that does this. I have been asked to bid on a couple but they have not pulled the trigger.

So 400VDC for shore power is probably not going to happen in our lifetimes.

The ABYC, and you all can contribute to that conversation, attempts to make the boat systems as safe as is possible against creditable failures. Hence the IT with the shield grounded to the source and the N, G and case grounded to the vessel's safety ground bus.

ABYC E-11 committee has discussed Dave Rifkin's issues with an isolation transformer and the consequences of the primary shorting to the case with no return to the source and found that if the IT is installed properly, this fault scenario is not creditable.

If you want to weigh in on E-11 during the review cycle, contact ABYC and ask to be put on the mailing list. You will receive notification of proposed changes, can propose changes and can take part in the entire process.

Or we can continue to beat this poor horse to death!
END RANT

Charlie,
Dave Rifkin sounds like he is much smarter than what ABYC and you all think about him.
The leakage in fresh water may not be enough to trip the ELCI when the primary shorts to case.
Neither the ELCI on board nor the ELCI or GFCI at the shore pedestal they will not sense any leakage current when the secondary shorts to the shield whether in fresh water or salt water.
Ahmet

[Ahmet Erkan]

Originally Posted by DotDun

How do we unwind the FUD this thread entails?

Mods, please delete the whole thread! ??

Fear Uncertainty Doubt (FUD)

Here is how you can deal with all three :
FEAR :
Be afraid (at least apprehensive) of what you do not know.
So this not too bad at all. If you do not know basic electric circuits, get a book and read it or take a course. Whatever you do, do not be afraid of people who are willing to explain what they claim. In my case, over and over again.

UNCERTAINTY :
Ask for verification. For example I asked the following.
******************************
Dear ABYC Technical Board,
I am requesting an explanation of protection from electrical shock drowning ESD for a diver working under a boat in a fresh water marina that has been wired per ABYC diagram #6 or #7 and connected to the fresh water marina shore power.
I am particularly interested about what happens when a short occurs inside the isolation transformer from shield to a high voltage turn in the secondary winding. (ie: A turn near the secondary live L1 or L2 terminals)
If an explanation is not possible and only yes/no response can be provided please use the format below :
1. If a short occurs as described above, it is possible that the diver can be subjected to a voltage gradient. (Yes/No)
2. If the resultant current after the short circuit failure as described above exceeds the limit of the ELCI CB shown on diagrams #6 or #7 in E11 will trip. (Yes/No)
Thank you in advance.
Sincerely
Ahmet Erkan
ahmet_erkan@sss-nc.com
Contact Us
Thank you for contacting us. We will review your submission in a timely manner
:
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I will let you know when ABYC responds.

DOUBT :
I had doubts that 5mA through my body could make me unable to swim. I set up a safe test jig and worked myself up to 5mA continuous current. (again do not try this at home without the proper safety equipment, better yet just believe me.) One minute exposure to 5mA was extremely uncomfortable, I would not do this test in water with an unknown path for charge flow through my body.
At this time I have no doubt in my mind that I do not want to be even remotely responsible for subjecting anybody to such an experience.

[DotDun]

Originally Posted by Ahmet Erkan

Fear Uncertainty Doubt (FUD)

Here is how you can deal with all three :
FEAR :
Be afraid (at least apprehensive) of what you do not know.
So this not too bad at all. If you do not know basic electric circuits, get a book and read it or take a course. Whatever you do, do not be afraid of people who are willing to explain what they claim. In my case, over and over again.

UNCERTAINTY :
Ask for verification. For example I asked the following.
******************************
Dear ABYC Technical Board,
I am requesting an explanation of protection from electrical shock drowning ESD for a diver working under a boat in a fresh water marina that has been wired per ABYC diagram #6 or #7 and connected to the fresh water marina shore power.
I am particularly interested about what happens when a short occurs inside the isolation transformer from shield to a high voltage turn in the secondary winding. (ie: A turn near the secondary live L1 or L2 terminals)
If an explanation is not possible and only yes/no response can be provided please use the format below :
1. If a short occurs as described above, it is possible that the diver can be subjected to a voltage gradient. (Yes/No)
2. If the resultant current after the short circuit failure as described above exceeds the limit of the ELCI CB shown on diagrams #6 or #7 in E11 will trip. (Yes/No)
Thank you in advance.
Sincerely
Ahmet Erkan
ahmet_erkan@sss-nc.com
Contact Us
Thank you for contacting us. We will review your submission in a timely manner
:
*****************************************
I will let you know when ABYC responds.

DOUBT :
I had doubts that 5mA through my body could make me unable to swim. I set up a safe test jig and worked myself up to 5mA continuous current. (again do not try this at home without the proper safety equipment, better yet just believe me.) One minute exposure to 5mA was extremely uncomfortable, I would not do this test in water with an unknown path for charge flow through my body.
At this time I have no doubt in my mind that I do not want to be even remotely responsible for subjecting anybody to such an experience.

I simply find it incredulous that a educated person would come onto a Internet forum of unsuspecting people and troll such FUD prior to taking it to the proper fora.

You have zero support for your thesis here and it appears zero support at ABYC.

You have not provided one actual case to support your fantasy.

[Ahmet Erkan]

Originally Posted by DotDun

I simply find it incredulous that a educated person would come onto a Internet forum of unsuspecting people and troll such FUD prior to taking it to the proper fora.

You have zero support for your thesis here and it appears zero support at ABYC.

You have not provided one actual case to support your fantasy.

DotDun,
I am not asking for support from ABYC just an answer to two simple questions that I have asked. (In their preferred Yes/No format)
The support I am asking from the forum is to wait and see what ABYC says before jumping to conclusions.
Do you have an isolation transformer on your boat? Did you disconnect the shore power ground from the underwater metals of your boat? (ie: Like advised in E11 diagrams #6 or #7) If you want proof that I am right or wrong, go and jumper the secondary L1 or L2 of your transformer to the shore power ground. If your ELCI CB trips then I will eat my words.
DotDun, if you keep banging your head on that brick wall, you are never going to understand any of this :-)
Ahmet

[DotDun]

Originally Posted by Ahmet Erkan

DotDun,
I am not asking for support from ABYC just an answer to two simple questions that I have asked. (In their preferred Yes/No format)
The support I am asking from the forum is to wait and see what ABYC says before jumping to conclusions.
Do you have an isolation transformer on your boat? Did you disconnect the shore power ground from the underwater metals of your boat? (ie: Like advised in E11 diagrams #6 or #7) If you want proof that I am right or wrong, go and jumper the secondary L1 or L2 of your transformer to the shore power ground. If your ELCI CB trips then I will eat my words.
DotDun, if you keep banging your head on that brick wall, you are never going to understand any of this :-)
Ahmet

Show evidence of a secondary ever shorting to the static shield (causing a problem).

[Ahmet Erkan]

Originally Posted by DotDun

Show evidence of a secondary ever shorting to the static shield (causing a problem).

DotDun,
I do not have recorded failure data but I can offer logical reasoning.
ABYC recommended a shield in the transformer and it is a shield at the same ampacity as the primary, therefore ABYC engineers thought it is possible for the primary to short to the shield. Henceforth if the shield could short to the primary, it could also short to the secondary.
Causing a problem? Duh I would think so. This short will create a voltage gradient up to 120Vac in US and 240Vac in European standard mains voltage divided by the depth of water under your boat.
So are you going to test the theory and prove me wrong?
Easy peasy since you are defending diagrams #6 and #7 with such a high level of trust that you probably have a boat wired per one of these diagrams.
By the way, although you think the ESD hazard is my fantasy, check that you do not have a diver or swimmer around your boat before you execute this simple test. Open the shore power CB and place a jumper from the shore power ground to the transformer secondary L1 or L2. Close the breaker and see if it trips right away. If either the onboard or pedastal CB trips I will go away and never bother you again.
OK do you understand all this? If you are not sure, do not do anything, just forget it and wait for ABYC to respond.
Ahmet

[transmitterdan]

Originally Posted by Ahmet Erkan

DotDun,
I do not have recorded failure data but I can offer logical reasoning.
ABYC recommended a shield in the transformer and it is a shield at the same ampacity as the primary, therefore ABYC engineers thought it is possible for the primary to short to the shield. Henceforth if the shield could short to the primary, it could also short to the secondary.
Causing a problem? Duh I would think so. This short will create a voltage gradient up to 120Vac in US and 240Vac in European standard mains voltage divided by the depth of water under your boat.
So are you going to test the theory and prove me wrong?
Easy peasy since you are defending diagrams #6 and #7 with such a high level of trust that you probably have a boat wired per one of these diagrams.
By the way, although you think the ESD hazard is my fantasy, check that you do not have a diver or swimmer around your boat before you execute this simple test. Open the shore power CB and place a jumper from the shore power ground to the transformer secondary L1 or L2. Close the breaker and see if it trips right away. If either the onboard or pedastal CB trips I will go away and never bother you again.
OK do you understand all this? If you are not sure, do not do anything, just forget it and wait for ABYC to respond.
Ahmet

Ahmet,
I believe Mr. Rifkin's logic is flawed. The shield is usually closer to the primary than the secondary with significant physical barriers between shield and secondary. There is next to zero possibility for a secondary to shield short. Since we have no actual example of that happening that suggests the probability is remote at best.

Another "feature" of the isolation transformer is the reduction of lightning induced damage to on-board equipment via conducted energy from the mains. The shield forms an electro-static barrier shunting impulse energy away from the boat's AC system feeding it back to earth via the safety ground. If we do as Mr. Rifkin suggests this excellent feature is completely defeated. In fact, the probability of arcing damage within the transformer and the on-board systems due to lightning is increased by doing as Mr. Rifkin suggests.

There is also a possibility for an ELCI on the boat to develop a short between the line and safety ground. What should we do about that? How about a leak between line and safety ground within the shore->boat cable? Any of these more likely events create risk to a swimmer if using Mr. Rifkin's recommendation but not if using the ABYC recommendation.

An isolation transformer built and installed per ABYC recommendations is extremely safe and protects against many fault conditions. And, in my opinion, is much safer than bringing the earth safety ground down into the bowels of the boat. It is pretty hard to have current flow in two circuits that are never connected together.

My opinion is that Mr. Rifkin has a solution in search of a non-problem. He also has apparently not thought about the entire system and has made a recommendation that is not very well thought out, again, in my opinion. I predict ABYC will decline to be dragged into the discussion. Most likely they will ignore this nonsense. At least I hope so.

[ramblinrod]

Originally Posted by Ahmet Erkan

Steve,
How about a radically different boat powering method for marinas?
Install modern power conversion equipment that converts the unregulated mains power to a regulated and isolated 400Vdc.
The shore power cables will reduce to 1/4 the size.
This is a standard design for wide input range universal ac/dc power supplies so both the shore based and the onboard equipment are already mass produced and cost effective.
Instead of a 60Lbs very expensive transformer on board all you need is a 6Lbs unit at a fraction of the cost.
Once the 400Vdc is on board you can have a low cost 300A charger or a low cost 3.6kW inverter or both.
Just a thought.
Ahmet

Dude, I am not hitting anybody anywhere.

I am trying to be respectful while you seem to be becoming unglued.

If you don't wish to post stuff you will regret, or that you don't want anyone to respond to, there is a very easy solution for that, that won't take any of your time.

I am certainly not one to stifle creative or critical thinking, innovation, and invention; exactly the opposite, I admire those kindred spirits who challenge the status quo.

However, your current approach doesn't seem to be garnering the results you desire, unless your desire is just to continue arguing a point ad infinitum ad nauseum, that nobody is buying.

Using that same high level of critical thinking, what do you think is your best move right now:

A) Keep chewin' an old cud.

B) Move on to greener pasture.

[CharlieJ]

I respect D. Rifkin's opinion, I have studied his white paper, I took part in the discussions at the ABYC meeting and I disagree with his conclusions. My conclusion is that a fault from the primary windings to the metal case of a properly constructed and installed isolation transformer is not creditable.

And note, as others have, that there is not a single documented case of your fault scenario occurring in our industry.

Post #111

Dave Rifkin sounds like he is much smarter than what ABYC and you all think about him.

Finally, your assessment of how I think about Dave's knowledge and expertise is not based on fact and is also very deeply flawed.

[Ahmet Erkan]

Originally Posted by CharlieJ

I respect D. Rifkin's opinion, I have studied his white paper, I took part in the discussions at the ABYC meeting and I disagree with his conclusions. My conclusion is that a fault from the primary windings to the metal case of a properly constructed and installed isolation transformer is not creditable.

And note, as others have, that there is not a single documented case of your fault scenario occurring in our industry.

Post #111


Finally, your assessment of how I think about Dave's knowledge and expertise is not based on fact and is also very deeply flawed.

Dear CharliJ,
You are right, it was an inaccurate generalization to say “you all” in my response. Most of the participants that claim isolation transformers (IT) are safe seem to think Captain Rifkin is incorrect. You may not be in that group or you may agree with some items and disagree with others. Again, I apologize for the unfair generalization.
Actually, I have no idea what was said and by whom in the ABYC E11 reviews but let me make a summary review of the E11 recommended boat wiring diagrams and you tell me if Captain Rifkin made similar comments?

Safe for the diver means, while the boat is connected to shore power any electrical failure on board shall cause only a low voltage (ie: less than 12V) to appear between shore power grounding conductor and the underwater metals of the boat.
Safe for the crew means, if a wet crew member (ie: standing in the bilge water) comes in contact with any live AC conductor (ie: 120Vac) an ELCI CB will trip if the current through the crew member is greater than the ELCI trip current. (ie: 30mA)
GI = Galvanic Isolator TI = Isolation Transformer.
Here is my summary review :
Diagrams 1,2,3 & 4 (GI only) Safe for the diver and safe for the crew.
Diagrams 5 & 8 (GI and IT) Safe for the diver and NOT SAFE FOR THE CREW
Diagrams 6 & 7 (IT only) NOT SAFE FOR THE CREW, NOT SAFE FOR THE DIVER

Note that the hardware becomes NOT SAFE whenever the IT is introduced. Complications such as dual shields, isolated neutrals, a second ELCI at the secondary circuits etc. are required to push the transformer to become marginally safe.
Ahmet