Onboard Isolation Transformer vs Safety

[smac999]

Like I already posted. Make the main incoming breaker an elci. In the super rare, never going to happen Case if the transforme input hot shorting to a metal case. The elci will trip instantly.

[ramblinrod]

Originally Posted by smac999

Like I already posted. Make the main incoming breaker an elci. In the super rare, never going to happen Case if the transforme input hot shorting to a metal case. The elci will trip instantly.

Actually, if adding an Isolation Transformer (that wasn't previously there), one MUST bring the entire AC system up to current standard, (which includes an ELCI), for the modified system to be ABYC compliant.

Per ABYC, an old electrical system that was compliant to the standard of the day, but not current standards, can stay as is.

But as soon as one makes a modification (vs maintenance or repair) the entire system must be brought up to current standards for the mod to be compliant.

[Ahmet Erkan]

Originally Posted by Paul Elliott

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.

Hi Paul,
Do not know how I missed your post from page 2. One of the rare posts where rational points are made.
Paul is going to read this post and see that in diagrams 6 and 7 of E11 there are more opportunities for the underwater metals to attain a high AC potential referenced to shore power ground. (ie: not just the shore power hot conductor shorting to the chassis of the transformer.)
A second shield wrapped over the secondary and bonded to the neutral of secondary is needed.
When the shield that is bonded to shore power ground shorts to the secondary winding the secondary winding gets referenced to shore power ground and the underwater metals that are connected to the secondary neutral are at high voltage and no longer isolated from the shore power. The hazard voltage is dependent on which turn of the secondary winding has shorted to the shield. The diver is sandwiched between the shore power ground at his/her feet and close to the now energized underwater metals. (Actually maybe touching them)
The probability of this failure mode to happen when the diver happens to be working at the bottom of your boat is indeed very low, but if the failure does happen and it is not detected your boat becomes a disaster waiting to happen, especially in fresh water.
And no the ELCI CB is not going to protect the diver in fresh water.

MESSAGE :
Stop buying heavy isolation transformers thinking that they make it safe to disconnect the shore power grounding conductor, and demand from the industry to improve their overpriced galvanic isolators that have an inferior performance.
1. The galvanic isolator shall provide safety for divers or swimmers around the boat with no single point failures that can be an electrocution hazard. (especially in fresh or brackish water)
2. The galvanic isolator shall provide isolation comparable to an isolation transformer.
3. The galvanic isolator shall warn the user when a failure occurs and the safety of your boat has degraded to a single point failure state.
4. The galvanic isolator shall shunt trip the boat's shore power breaker if the shore power grounding conductor fails open. (A common failure at marinas as pointed in Captain Rifkin's presentation which was provided in an earlier post)
5. The galvanic isolator shall warn the user if AC stray current through the galvanic isolator exceeds a TBD limit.
6. The galvanic isolator shall warn the operator and shunt trip the boat's shore power
7. To be continued.

[ramblinrod]

Originally Posted by Ahmet Erkan

[SIZE=3]
And no the ELCI CB is not going to protect the diver in fresh water.

The ELCI should trip before the swimmer is paralyzed (ESD) or electrocuted in fresh water.

The Art of Problem Solving 101, Lesson 1...

Every solution creates at least one more problem.

[CharlieJ]

Ahmet
I suggest you re-read #42.

Regarding your suggestions in #48:
A GI will never be able to provide the same isolation as an IT.

A GI can block about 2.2VDC of galvanic current. A GI can not block stray DC current being delivered by the safety ground wire.

An IT provides proper polarization to the vessel no matter how the shore power pedestal gets mis-wired.

As I explained in #42, your ideas about sampling the safety ground for integrity and for level of leakage was partially implemented by ABYC A-28 several years ago and turned out to be a very expensive failure for the industry. The fail safe GI was developed as a result of this "experiment".

Finally, with the requirement for an ELCI onboard by ABYC and a GFP in the shore power supply by NFPA 70, testing for safety ground integrity will, by the nature of the test, nuisance trip these devices.

[Ahmet Erkan]

Originally Posted by ramblinrod

The ELCI should trip before the swimmer is paralyzed (ESD) or electrocuted in fresh water.

The Art of Problem Solving 101, Lesson 1...

Every solution creates at least one more problem.

Dear Rod,
I have very carefully (with fail safe current limiting) worked up to 5mA sustained electrocution (minimum one minute) from my right foot to right hand. At 3mA it was very uncomfortable. At 4mA the knuckles in my right hand were convulsing. At 5mA my teeth were chattering. It is nothing like accidentally touching high voltage while working and it stops as soon as you pull your hand with reflex. Even if you have an ELCI or GFCI at the primary a lower current below the trip level in fresh water but continuously existing through the divers body will cause the diver to be unable to breathe or swim away.

Don't try this test at home :-)

[ramblinrod]

Originally Posted by Ahmet Erkan

Dear Rod,
I have very carefully (with fail safe current limiting) worked up to 5mA sustained electrocution (minimum one minute) from my right foot to right hand. At 3mA it was very uncomfortable. At 4mA the knuckles in my right hand were convulsing. At 5mA my teeth were chattering. It is nothing like accidentally touching high voltage while working and it stops as soon as you pull your hand with reflex. Even if you have an ELCI or GFCI at the primary a lower current below the trip level in fresh water but continuously existing through the divers body will cause the diver to be unable to breathe or swim away.

Don't try this test at home :-)

I never claimed any amount of electrical current passing through one's body was a joy ride.

(Well, as a kid we used to play with electric fences so there ya go.) ;-)


The point is, it is virtually impossible to develop a lethal condition if a properly functioning GFCI and/or ELCI is in circuit.


At the risk of repeating myself, attempting to achieve "ultimate safety" is a fools game.


"Working up to" and "instantaneous exposure" are 2 very different things.

I have tripped many a GFCI with my body, and never felt a thing.

[transmitterdan]

Ahmet,

There is virtually no way to get a shore ground to secondary short in a properly designed isolation transformer. You are trying to solve a nonexistent problem.

In order to get your risk/fear recognized as a valid one you need to show at least one case where it came to fruition. I am aware of no case where an underwater swimmer was drowned due to a faulty isolation transformer. Do you know of such a case?

[transmitterdan]

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.

[Ahmet Erkan]

Originally Posted by CharlieJ

Ahmet
I suggest you re-read #42.

Regarding your suggestions in #48:
A GI will never be able to provide the same isolation as an IT.

A GI can block about 2.2VDC of galvanic current. A GI can not block stray DC current being delivered by the safety ground wire.

An IT provides proper polarization to the vessel no matter how the shore power pedestal gets mis-wired.

As I explained in #42, your ideas about sampling the safety ground for integrity and for level of leakage was partially implemented by ABYC A-28 several years ago and turned out to be a very expensive failure for the industry. The fail safe GI was developed as a result of this "experiment".

Finally, with the requirement for an ELCI onboard by ABYC and a GFP in the shore power supply by NFPA 70, testing for safety ground integrity will, by the nature of the test, nuisance trip these devices.

Charlie,
I re-read #42 thank you. (When Moby Dick was a sardine, I love it :-) I heard the one about the angels on a pin head before. This is what happens when one get's old :-)
It astonishes me that all the subject matter experts gathered around to write E11 allowed figures 6 and 7 to pass. One can claim that the ELCI makes it all good but that is not true either. A short from the shield to secondary is going to source the power to the diver such that the ELCI cannot sense it due to the transformer action. Also they need to upscope the GI requirements and add a GI to figures 6 and 7. (Sorry for acting like a broken record, I really believe in the proper GI's as well as the IT.)
It appears as you have a communication channel to ABYC, they need to add a second shield to the IT bonded to the secondary neutral. (I think I said that earlier)
By the way, contact me directly if you want me to elaborate further. Captain Rifkin has my e-mail address.
Now it is time for a glass of wine.
Cheers
Ahmet

[CharlieJ]

transmitter dan #53

In water deaths are not from electrocution.

This statement is fairly inaccurate.

Electric shock drowning (not "electrocution") is caused by subjecting a human to an electric field in the water that produces enough current to interrupt the normal firing mechanism of the heart. The human heart operates on microamps of current. So it is not too much of a stretch to see that if you subject it to many milliamps, that bad things will happen.

ESD was aptly named about 18 years ago when Kevin Ritz's son was killed when he entered an electric field in fresh water. The coroner initially labeled the cause of death as drowning. Kevin's son was wearing a life jacket (PFD) and his head never went below the surface of the water.. This instance became the impetus for ESD eradication including the requirement for ELCI's aboard boats and GFP in shore power supplies.

[transmitterdan]

Originally Posted by Ahmet Erkan

It astonishes me that all the subject matter experts gathered around to write E11 allowed figures 6 and 7 to pass. One can claim that the ELCI makes it all good but that is not true either. A short from the shield to secondary is going to source the power to the diver such that the ELCI cannot sense it due to the transformer action. Also they need to upscope the GI requirements and add a GI to figures 6 and 7.
Ahmet

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]

Originally Posted by CharlieJ

transmitter dan #53

This statement is fairly inaccurate.

Electric shock drowning (not "electrocution") is caused by subjecting a human to an electric field in the water that produces enough current to interrupt the normal firing mechanism of the heart. The human heart operates on microamps of current. So it is not too much of a stretch to see that if you subject it to many milliamps, that bad things will happen.

ESD was aptly named about 18 years ago when Kevin Ritz's son was killed when he entered an electric field in fresh water. The coroner initially labeled the cause of death as drowning. Kevin's son was wearing a life jacket (PFD) and his head never went below the surface of the water.. This instance became the impetus for ESD eradication including the requirement for ELCI's aboard boats and GFP in shore power supplies.

Charlie,

Thank you for correcting me. I hope the point is made though that the danger to young swimmers is worse in fresh water than to adults on land.

ESD is a serious problem and I see stupid parents letting their kids jump into the water off lake marina docks all the time. I watch these kids as closely as I can for signs of distress. When I try to explain the danger to their parents they think I am crazy. It’s hard to make them understand the seriousness of the risk they are taking. There needs to be mandatory signage at fresh water docks about the danger.

[DotDun]

Originally Posted by Ahmet Erkan

Charlie,
I re-read #42 thank you. (When Moby Dick was a sardine, I love it :-) I heard the one about the angels on a pin head before. This is what happens when one get's old :-)
It astonishes me that all the subject matter experts gathered around to write E11 allowed figures 6 and 7 to pass. One can claim that the ELCI makes it all good but that is not true either. A short from the shield to secondary is going to source the power to the diver such that the ELCI cannot sense it due to the transformer action. Also they need to upscope the GI requirements and add a GI to figures 6 and 7. (Sorry for acting like a broken record, I really believe in the proper GI's as well as the IT.)
It appears as you have a communication channel to ABYC, they need to add a second shield to the IT bonded to the secondary neutral. (I think I said that earlier)
By the way, contact me directly if you want me to elaborate further. Captain Rifkin has my e-mail address.
Now it is time for a glass of wine.
Cheers
Ahmet

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.

[transmitterdan]

Does this story give you chills? It does me.

http://www.kten.com/story/38238169/p...at-lake-texoma