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Old 06-07-2018, 18:37   #61
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Re: Onboard Isolation Transformer vs Safety

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Also, there is no DC path from the boat to shore so a GI would be useless.

Thanks for clarifying that and the other questions.
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Old 06-07-2018, 21:07   #62
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Re: Onboard Isolation Transformer vs Safety

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Originally Posted by transmitterdan View Post
Rod,

In water deaths are not from electrocution. It is from drowning because the swimmer is not able to swim properly. It takes much less than lethal current to incapacitate a swimmer. Particularly young unskilled swimmers.
Actually many in water deaths are from electrocution. Some in water deaths in fresh water are due to ESD, that I referred to in post 49.
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Old 07-07-2018, 02:19   #63
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Re: Onboard Isolation Transformer vs Safety

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Actually many in water deaths are from electrocution. Some in water deaths in fresh water are due to ESD, that I referred to in post 49.

I agree with you. I also suspect some reported drownings in fresh water marinas are actually ESD events that are not investigated as such.

Is there a device that can be put on the shore connection that will record leakage over time? Most boats don’t leak current all the time.
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Old 07-07-2018, 04:43   #64
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Re: Onboard Isolation Transformer vs Safety

From time to time I learn something interesting on CF. ESD seems a significant problem and it should make a good topic for a lecture at my local power squadron meeting. We are on the Ohio river and most of the boaters be in there or one of the local lakes is all fresh water. Thank you Charlie.

BTW, I am very happy with my ISO on the boat. It was installed more for elimination of stray and galvanic corrosion than any protection from ESD. I don't swim in a marina, ever! An ISO on your boat isn't protection from ESD anyway as the path of the currents can originate from shore, through you and to some other point, perhaps the neighbor's boat.
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Old 07-07-2018, 05:12   #65
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Re: Onboard Isolation Transformer vs Safety

As a kid, many years ago I was almost a victim of ESD. We were swimming in fresh water in Michigan at our marina, and as we were going from one set of docks to another I began to feel a little odd, and tingly/numbness...hard to describe many years later. My brother who was with me said he felt the same, we swam back in the opposite direction. We told our parents, and that was the end of marina swimming. Looking back it was not something people were aware of in the mid 70's, I am thankful to this day we did not swim further.
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Old 07-07-2018, 05:41   #66
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Re: Onboard Isolation Transformer vs Safety

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Originally Posted by transmitterdan View Post
I agree with you. I also suspect some reported drownings in fresh water marinas are actually ESD events that are not investigated as such.

Is there a device that can be put on the shore connection that will record leakage over time? Most boats don’t leak current all the time.
Sorry in advance for typos, posting from POS iPhone.
If you put a clamp on ammeter over you shore power cord, the line and neutral mag fields cancel each other out (and of course ground shouldn’t be carrying current). So if the meter reads 0, no leakage; if the meter reads more than 0, leakGe is present. The issue was s the leakage could come from intermittent loads like water heaters (notorious for ground faults) or HVAC/R.

If the meter has a “max hold” function, that will catch it. I sometimes throw my meter on suspect boats as I walk by and advise marina staff if I get a reading. It’s not perfect because a faulty circuit may not be switched on.

For marina power, the best method to a 1 ft square copper plate immersed in the water with the voltmeter connected to that and power post ground terminal. If you measure anything, something is live in the water. The closer you move the plate to the source (current path) the higher the reading.
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Old 07-07-2018, 06:11   #67
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Re: Onboard Isolation Transformer vs Safety

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Originally Posted by transmitterdan View Post
Ahmet,

Your analysis is faulty. The source of current from the secondary is not from the shore. Thus no current will flow from the secondary back through the water to the earth. All of the current will stay inside the boat. The only way for current to flow in the water is if the shore hot lead connects to the boat. And the ELCI would interrupt that in the extremely unlikely event.

Also, there is no DC path from the boat to shore so a GI would be useless.

transmitterdan,
After finding out I am correct, you are going to be embarrassed for saying all that you have said.
I am so curious how a person even with a rudimentary understanding of electric circuits could argue against the points below:
1. The voltage gradient in fresh water that we are discussing in this forum is between the shore power ground and the underwater metals of a boat. It is said that if a human enters this voltage gradient while the said boat is using shore power at a fresh water marina, he or she is likely to encounter electric shock drowning (ESD). I am guessing fish are safe because they are short so a lower voltage will appear across them. Tall divers and low water not so lucky.
2. ABYC E11 Diagram 6 (page 36) and diagram 7 (page 38) show the shore power ground routed and connected to the shield between the primary and secondary in the isolation transformer (IT)
3. The diagrams mentioned above also show the secondary neutral of the IT connected to the underwater metals of the boat.
4. If the shield shorts to secondary of the IT, the voltage induced in the portion of the winding between the short and the neutral will be placed across the diver and create the voltage gradient.
5. Energy transferred to the voltage gradient under the vessel will come from the shore power source with equal currents at the primary neutral and hot conductors of the IT. Thus the ELCI or GFCI on board or at the pedestal will not be able to sense a current differential and will not trip.


USE A GALVANIC ISOLATOR
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Old 07-07-2018, 06:36   #68
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Re: Onboard Isolation Transformer vs Safety

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Ahmet,

I'm really struggling whether you are just naive at how standards bodies work or you are arrogant enough to believe ABYC will change their spec based on what you say.

FYI, ABYC is an ANSI accredited standards organization, which means all their specifications are reviewed by all interested parties and the outcome is based on consensus of the group.

As some of us have been saying, your case would be much stronger if you provide forensic evidence that your failure scenario has ever actually happened.

Good Luck changing the spec.

DotDun,
If ABYC changed their documents based on what I say, my level of respect for ABYC will be lowered. However, if ABYC found out about the things I have said in this discussion and instead of dismissing them immediately like you are doing, if an ABYC engineer contacted me (maybe privately) and sent me an engineering change request (ECR) form, my level of respect for ABYC will become even higher.
Remember, freedom of speech comes together with freedom to believe or not believe. Let the people decide themselves about whether to believe me or not.
Have a nice day DotDun.

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Old 07-07-2018, 07:10   #69
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Re: Onboard Isolation Transformer vs Safety

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Originally Posted by Ahmet Erkan View Post
DotDun,
If ABYC changed their documents based on what I say, my level of respect for ABYC will be lowered. However, if ABYC found out about the things I have said in this discussion and instead of dismissing them immediately like you are doing, if an ABYC engineer contacted me (maybe privately) and sent me an engineering change request (ECR) form, my level of respect for ABYC will become even higher.
Remember, freedom of speech comes together with freedom to believe or not believe. Let the people decide themselves about whether to believe me or not.
Have a nice day DotDun.

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Old 07-07-2018, 07:53   #70
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Re: Onboard Isolation Transformer vs Safety

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Originally Posted by Ahmet Erkan View Post
transmitterdan,
After finding out I am correct, you are going to be embarrassed for saying all that you have said.
I am so curious how a person even with a rudimentary understanding of electric circuits could argue against the points below:
1. The voltage gradient in fresh water that we are discussing in this forum is between the shore power ground and the underwater metals of a boat. It is said that if a human enters this voltage gradient while the said boat is using shore power at a fresh water marina, he or she is likely to encounter electric shock drowning (ESD). I am guessing fish are safe because they are short so a lower voltage will appear across them. Tall divers and low water not so lucky.
2. ABYC E11 Diagram 6 (page 36) and diagram 7 (page 38) show the shore power ground routed and connected to the shield between the primary and secondary in the isolation transformer (IT)
3. The diagrams mentioned above also show the secondary neutral of the IT connected to the underwater metals of the boat.
4. If the shield shorts to secondary of the IT, the voltage induced in the portion of the winding between the short and the neutral will be placed across the diver and create the voltage gradient.
5. Energy transferred to the voltage gradient under the vessel will come from the shore power source with equal currents at the primary neutral and hot conductors of the IT. Thus the ELCI or GFCI on board or at the pedestal will not be able to sense a current differential and will not trip.


USE A GALVANIC ISOLATOR
The GI will pass AC.
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Old 07-07-2018, 09:15   #71
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Re: Onboard Isolation Transformer vs Safety

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Originally Posted by DotDun View Post
The GI will pass AC.

Bravo, you are catching on DotDun.
The GI is connected in parallel with the diver and the AC leakage will pass through the GI instead of through the diver, and protect him/her from death by ESD.
Maybe you can handle more information on how to build a better transformer?
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Old 07-07-2018, 11:40   #72
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Re: Onboard Isolation Transformer vs Safety

Ahmet,

I am an electrical engineer with many years experience. I design high power systems from 1kw to many megawatts.

I will never be embarrassed when proven wrong. Being wrong is how we learn

1) A galvanic isolator has absolutely no effect on swimmers getting shocked. It neither makes shock risk worse or better. The only function a GI has is to block DC current in the shore power ground wire. This helps protect some boats from corrosion. But it does not cure all corrosion problems. Again, it does absolutely nothing to prevent shock.

2) The isolation transformer blocks DC and it adds additional protection against shock to swimmers. When using an isolation transformer no GI is needed.

You clearly do not understand electricity or electric field theory. The way a swimmer gets shocked is by an electric field in the water. The field comes from the potential between the shore hot wire and the earth because the shore power is referenced to earth. The safety ground wire is there to reduce any electric field in the water. When the safety earth wire is not present or has high resistance the in water field is increased leading to ESD. A GI does nothing to effect this state of affairs.

The secondary of an isolation transformer cannot be the source of swimmer ESD because the secondary side is not referenced to the earth. The electric field never leaves the confines of the boat. This is true regardless whether the earth safety ground is accidentally connected to the boat or not. But the earth ground should not be connected to the boat except at the transformer shield and nothing else.

A boat with an isolation transformer is very safe even in all failure modes. The worst failure mode would be the hot side primary shore power shorting to the secondary. That is why there is a metal shield connected to earth standing between primary and secondary.

Again, for other readers of this thread. Don’t pay any attention to internet arguments about electricity. Follow all local codes and manufacturer’s instructions precisely. Do not accept some unknown person’s contrary advice. It is often wrong.
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Old 07-07-2018, 15:24   #73
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Re: Onboard Isolation Transformer vs Safety

Hello all,
At this time I want to take a break and wait for a response from the ABYC engineer.
Although I disagree with just about everything technical that transmitterdan has said, I support the excellent advice in his last post that unless you are a subject matter expert, it is not a good idea to deviate from the current ABYC or ABS recommendations about electrical safety, let alone take advice from an unknown person making proclamations from a soap box on the internet.
My advice to fellow sailors who have their boats wired per Diagrams 6 or 7 of ABYC E11 and are moored at fresh water marinas is to unplug their boats from shore power while a diver or themselves is cleaning the bottom of their boat. Also place a big sign at the stern of your boat that states something like “ELECTRICAL SHOCK HAZARD MAY EXIST, PLEASE DO NOT SWIM NEAR BOATS”.
Lastly, I really understand what SV Siren says about the horrors of ESD because it is a very rare event and if you are the unlucky person suddenly you are drowning and you have no control of your spasming muscles to swim away and save yourself. As you are drowning in helpless agony I am sure you are very angry and don’t give a flying fxxk about who is the master electrical engineer or who is right or who is wrong on this forum.
OK you all, have a great weekend and we will continue later.
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Old 07-07-2018, 16:18   #74
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Re: Onboard Isolation Transformer vs Safety

I apologize about the f bomb.
It was not appropriate and won't happen again.
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Old 08-07-2018, 06:20   #75
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Re: Onboard Isolation Transformer vs Safety

Transmitterdan
In fact, NFPA 70 (NEC) now requires the following sign at any compliant marina or boat dock that provides shore power to its moored vessels:

555.24 Signage. Permanent safety signs shall be installed to
give notice of electrical shock hazard risks to persons using or
swimming near a boat dock or marina and shall comply with all
of the following:
(1) The signage shall comply with 110.21(B)(1) and be of
sufficient durability to withstand the environment.
(2) The signs shall be clearly visible from all approaches to a
marina or boatyard facility.
(3) The signs shall state “WARNING — POTENTIAL SHOCK
HAZARD — ELECTRICAL CURRENTS MAY BE
PRESENT IN THE WATER.”
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