Onboard Isolation Transformer vs Safety

[Ahmet Erkan]

Originally Posted by ramblinrod

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.

Dear Rod,
Here is what I said. “Rod, if you have to hit under the belt no problem, bring it on anyway.”
I was just trying to say even if you did hit under the belt, I am not going to get “unglued”, miffed, emotionally stressed or react with some other non-sailor behavior.
Participants in this thread seem to get the opposite of whatever I try to get across.
Also, “bring it on” part was probably result of temporary overconfidence due to extra vino.
Sooooorry.
Are we still friends ? If so read on…….
I probably brought up the 400Vdc thing because I was getting bored. Since you said you like thinking outside the box, why don’t you start a thread on power factor corrected wide input voltage/frequency boat power at 400Vdc?
I promise to go to a charm school before making any comments.
Cheers
Ahmet

[Colin A]

I believe in studies done by the coast guard part of the reason for the 30ma trip is the path of the current is spread out in the water and bonded metal. So typically a swimmer would be safe as the current dissipates even at the 25 or so milliamps most ELCI's trip at.

Here is a link to ABYC's get involved section for PTC's
https://abycinc.org/page/GetInvolved?
The standards are written by a group of industry professionals, consumers etc. Not one engineer working in a room.



If we assume an ELCI is a help in fixing fault currents the issue of a primary to case fault is likely not going to be big problem. Really that seems to just leave the secondary to shield as an issue.

I'm not an engineer but I have been working on electrical in boats for over a decade now so tell me if that's wrong I won't mind.

[CharlieJ]

Colin A Post #122

+1

And I encourage all concerned to become involved in the development of the Standards.

[Colin A]

As a follow up if your a crazy belt and suspenders guy. ELCI/RCD at inlet then an isolation transformer. Then ground fault detector on ground bond wire as well as the feeders from the transformer. You could even use one with a shunt trip. A unit like a Bender 460 would allow both to be monitored from a single unit.

In this case the CT would go over the current carrying conductors that feed the distribution system. That would catch most leakage except an internal transformer leak to shield which should show up on a CT over the ground bond connection wire.

I quoted a system like that for some one building a Aluminum boat but they never ordered it.

[DotDun]

Originally Posted by Colin A

As a follow up if your a crazy belt and suspenders guy. ELCI/RCD at inlet then an isolation transformer. Then ground fault detector on ground bond wire as well as the feeders from the transformer. You could even use one with a shunt trip. A unit like a Bender 460 would allow both to be monitored from a single unit.

In this case the CT would go over the current carrying conductors that feed the distribution system. That would catch most leakage except an internal transformer leak to shield which should show up on a CT over the ground bond connection wire.

I quoted a system like that for some one building a Aluminum boat but they never ordered it.

Why not an ELCI with only the boat ground (at the IT) running thru the sense coil?

[transmitterdan]

In a similar thread several years ago it was proposed to remove the earth ground altogether from the IT?

Before someone’s head explodes, consider there is still an ELCI that will catch any and all leakage to earth from the shore side. There cannot be any leakage to earth from the secondary side because the secondary has no earth connection. Any current that leaves the boat through the water has to come from shore and the ELCI will catch that.

[DotDun]

Originally Posted by DotDun

Why not an ELCI with only the boat ground (at the IT) running thru the sense coil?

Or just run the boat ground thru the sense coil along with the primary L/N or L1/L2.

[Aethelwulffe]

While I have not read every post in this long thread, I would like to remark on the premise of the initial question:

1. Isolation transformers are transformers. That is it. Alternating current at whatever the shore side is fed through a 1:1 set of windings. This ensures that the POLARITY of your boat-side juice is correct (if YOU are wired right) but despite plenty of other supposed features to these devices, that is ALL they do. They MAY include other devices such as a GFCI which COULD prevent a shock, but a leaky 110 or 220 circuit hitting salt water is unlikely to instantly electrocute anyone...because the breaker would say something about it first, if no other reason.

2. Galvanic isolators are about DC current. This prevents an electrical system fault from allowing a nasty trickle of juice from one of your underwater bits of metal from corroding another underwater bit of metal. That is all. These do not guarantee that galvanic corrosion will not happen. It just takes care of a single scenario in which that might happen.
Normally, galvanic protection happens by either bonding all your underwater metal to all the other underwater metal with some wires that are TOTALLY SEPARATED from your DC circuits, and then hooked onto a sacrificial anode (zinc). This will never happen, as your engine is designed with block/chassis ground for the starter...unavoidable) and is certainly connected to underwater metal, if only by a seawater hose. The other way is to totally disconnect all underwater metal from anything else (isolation) so that there is no pathway. This is also a poor hope, because someone on the dock will be dumping juice into the water. In this case, you use an anode on every seacock, shaft, rudder, keel shoe or prop....and check them.
-This also has nothing to do with anyone getting shocked...though the full bonding thing can either help or hurt depending on the scenario. Bonding also does not help with lightning protection. It could help lightning to blow out every fitting in the boat, or nothing could happen...or.... -well, lightning just jumped a 7 million volt 3 million amp spark across 7 kilometers of open sky. Your 4' of copper cable doesn't mean squat. >50,000 volts and electricity is darn near unpredictable.

-So, you are worried about Alternating Current electrocution? GFCI right at the pole on the dock, and another hooked to your main panel. Then, turn off power to the whole dock if someone goes swimming, and watch out for lightning. Truth is, lightning can electrocute a swimmer, but it is REALLY HARD to do. All these different toys do absolute squat though. They are toys to sell to boat people that like to buy toys to screw onto their boats. Throw away toys and the associated wires and hose...then clean and improve the quality of what is there. That is your safety feature.

[Aethelwulffe]

Check your dock with a galvanometer and all your equipment with a megger. Can't borrow one from me, 'cause I gave mine away to a customer years ago. You find problems dockside, and then you still can't get anyone to fix them anyway. Better to just not even know, then go invest in zinc futures.

Stray currents happen. Tide, ferrous rock formations and differential metals in salt water can cause galvanic corrosion. Things are what they are.

[Colin A]

Originally Posted by DotDun

Why not an ELCI with only the boat ground (at the IT) running thru the sense coil?

ELCI breakers have the electronics powered by line voltage. If you had an ELCI like the North Shore saftey it should work fine. (edit also just remembered the smaller A series like Carling ELCI uses a external coil instead of internal so that could be made to work as well. )
One advantage to the Bender I believe you can adjust them down to pickup under 10MA fault so you could have a warning alarm and an actual fault alarm as it rises.

[Colin A]

Originally Posted by transmitterdan

In a similar thread several years ago it was proposed to remove the earth ground altogether from the IT?

Before someone’s head explodes, consider there is still an ELCI that will catch any and all leakage to earth from the shore side. There cannot be any leakage to earth from the secondary side because the secondary has no earth connection. Any current that leaves the boat through the water has to come from shore and the ELCI will catch that.

As I understand it modern surgical suites are wired that way. Isolation transformer with no ground reference.

[CharlieJ]

Posts #128 and #129 are full of mis-information and the advice should be avoided by all.

This ensures that the POLARITY of your boat-side juice is correct (if YOU are wired right) but despite plenty of other supposed features to these devices, that is ALL they do.

No, that is not all they do. As stated in the name of the device, the isolation transformer isolates the primary side, fed by the shore mains, from the secondary side where neutral and safety ground are bonded. The vessel's electrical system is totally isolated from the shore mains.

This will never happen, as your engine is designed with block/chassis ground for the starter...unavoidable)

Except in the very real cases where the engines are equipped with isolated ground starters.

and is certainly connected to underwater metal, if only by a seawater hose.

It appears that you are implying that the propulsion engine seawater system is connected via galvanic current to the water column. This is simply not true. Galvanic/cathodic protection current will not migrate more than about 2 to 3 diameters in a hose, pipe or annular space.

The rest of this post is just plain, weirdly wrong and/or misdirected.

Check your dock with a galvanometer

A galvanometer??? Good grief...how about a high resolution clamp on ammeter like a Yokogawa or Hioki. Leave the galvanometer in the high school physics lab.

...and all your equipment with a megger.

This is pretty unsound advice unless the technician knows precisely how to perform this potentially equipment destroying test.

[DotDun]

Originally Posted by transmitterdan

In a similar thread several years ago it was proposed to remove the earth ground altogether from the IT?

Before someone’s head explodes, consider there is still an ELCI that will catch any and all leakage to earth from the shore side. There cannot be any leakage to earth from the secondary side because the secondary has no earth connection. Any current that leaves the boat through the water has to come from shore and the ELCI will catch that.

I didn't connect shorepower ground to my static shield for 2-3 years after installation, left it disconnected at the inlet. Now I can't remember why I did connect it.

[Jammer]

Originally Posted by Ahmet Erkan

NOT SAFE FOR THE CREW, NOT SAFE FOR THE DIVER

I have read through this thread in its entirety.

I have an extensive theoretical and practical background in electrical systems design and installation.

I believe that Ahmet Erkan's comments in this thread, taken as a whole, are contrary to safety and are not in accordance with established practices or sound engineering judgment.


I do not believe it is in the public interest to engage in a point-by-point debate or rebuttal in a general-interest, public boating forum such as this, and I will therefore not be drawn into such a discussion.

[Unregistered-1]

Originally Posted by Jammer

I have read through this thread in its entirety.

I have an extensive theoretical and practical background in electrical systems design and installation.

I believe that Ahmet Erkan's comments in this thread, taken as a whole, are contrary to safety and are not in accordance with established practices or sound engineering judgment.


I do not believe it is in the public interest to engage in a point-by-point debate or rebuttal in a general-interest, public boating forum such as this, and I will therefore not be drawn into such a discussion.

Ahhh, this is just too tempting to take apart, but I think I will therefore not be drawn into such a discussion.