Isolating Transformers, The Earth wire connection conundrum

[s/v Jedi]

This is what Internet forums have become: defending "whatever" to the last drop of blood, not hindered by any real engineering qualifications, or worse, just enough basic knowledge to be dangerous, and all that just to frak it up. This has happened before and again and again, with the same players I may add. Readers who think they can learn something here are right. It just ain't anything about personal safety. This forum is for hanging out, nothing more

[sailorchic34]

BTW, Sorry I get a bit ah, well that B word, once and a while. I get tired having to justify myself over and over again. That's sometimes with engineers too, btw. Oh sure I'm not away's right and do suffer from brain farts from time to time. But this is not one of those times.

That's why I post a small part of my work experience on line. I'm not just a bimbo...

BTW, 46 CFR does have a small section on un grounded systems. But 46 CFR applies to commercial vessels only.

Personally I would love an isolation transformer on my boat. Jedi's system is quite elegant. But then again, I'm plugged into docks only a part of the time anyway.

[stillbuilding]

Originally Posted by s/v Jedi

This is what Internet forums have become: defending "whatever" to the last drop of blood, not hindered by any real engineering qualifications, or worse, just enough basic knowledge to be dangerous, and all that just to frak it up. This has happened before and again and again, with the same players I may add. Readers who think they can learn something here are right. It just ain't anything about personal safety. This forum is for hanging out, nothing more

Well Jedi, I understand the difficulties and frustration of discussing technical issues with amateurs or misinformed (like me) but it really is something of education and I have learned a lot from this thread. Keep up the good work.

[sailorchic34]

Originally Posted by FlyingCloud1937

Here's an odd tidbit, I happen to manage a 4 mil BTU Steam Boiler in an old 1914 building....it's called a Brick Yard Boiler
Lloyd

I've designed several steam plants in the 170 MBH / 5000 BHP range, plus Site distribution and all equipment connections, etc. One was for a Green Field Bio-pharma plant, the other was for a hotel casino on the strip in Vagas. I also designed 10,000 ton chiller plants. Actually I'm not sure how many I've done, those were just the biggest. Fun stuff.

BTW that wet basement with metal case, with a GFI on two wires, Its still safe. Not code, but safe. Without the GFI, its shocking, just shocking

OH I'm so done here. Ya'll have fun.

[downunder]

Originally Posted by stillbuilding

Well Jedi, I understand the difficulties and frustration of discussing technical issues with amateurs or misinformed (like me) but it really is something of education and I have learned a lot from this thread. Keep up the good work.

[EngNate]

Holy Smokes! is this a popular subject!

Let me put in one or two things:

In an AC power system the point that is ultimately "ground" is established at the power source: a generator, transformer, or an inverter. The connection to earth is to include the earth in the safety grounding system. Earth, or sea, does not establish the ground, it is a grounded part. The underwater metal parts on a boat are to be connected to the safety grounding system so that in the event of a fault these cannot be the source of current that would harm persons in the water. The connection to earth is in no way required for the safety of persons onboard.

The purpose of an isolation transformer is to allow the isolation of the boat's safety grounding system, and thus its underwater metal parts, from those of other boats, the dock and other land wiring.

The diagram shown at the top of this thread is right in my book.

Cheers!

[goboatingnow]

Originally Posted by EngNate

Holy Smokes! is this a popular subject!

Let me put in one or two things:

In an AC power system the point that is ultimately "ground" is established at the power source: a generator, transformer, or an inverter. The connection to earth is to include the earth in the safety grounding system. Earth, or sea, does not establish the ground, it is a grounded part. The underwater metal parts on a boat are to be connected to the safety grounding system so that in the event of a fault these cannot be the source of current that would harm persons in the water. The connection to earth is in no way required for the safety of persons onboard.

The purpose of an isolation transformer is to allow the isolation of the boat's safety grounding system, and thus its underwater metal parts, from those of other boats, the dock and other land wiring.

The diagram shown at the top of this thread is right in my book.

Cheers!

No , the purpose of an ABYC wired IT transformer is to do as you say. The purpose of S/V Jedis is to enhance safety on board and for swimmers.

There is no requirement as far as I am aware to establish a specific seawater earth connect in ABYC. Furthermore where a shore earth is continuous into the boat in say a non IT environment , most codes are against establishing a local earth/seawater ground


In many mains power systems, because the supply is fed trough transformers, local earths must be re-established.

Furthermore the very fact of trying underwater metas together and connecting them into the protective earth system can actually exacerbate the issue of electrocution, especially where high resistance paths in the shore earth wire develop. Without whole boat RCDs there is little protection from electrocution in the water. In an IT situation the safest for swimmers is a fully floating system , where earth is not in the return path , hence it can never carry fault current.


The issue being debated is the difference , in an IT installation , between a fully floating system , it's advantages and disadvantages and a version where a local seawater/earth ground is re-established

And if you think floating systems are unusual , consider the ubiquitous Honda generator !!

( kinda like , double insulated tools or not )

See my diagrams at the very start.

Dave

[pbiJim]

Originally Posted by Fuss

It would be nice (but probably not possible) if we could now have a short summary of the acceptable scenarios.

I would also like to see this, now that so much has been hashed out.

In addition, I would ask that each possible scenario be listed with it's advantages & disadvantages. Even in a case where a particular system has 10 advantages & only 1 disadvantage, it think it is still important to list the disadvantage so that someone wanting to apply that system in a particular scenario has the ability to see the possible danger that his specific situation may present. Simply listing a particular system as "the best" & not listing the possible disadvantages does not do full service to the reader.

In cases where there is disagreement about the existence of a specific hazard, I would ask that both sides of the story be listed so that the reader can evaluate it for himself.

I think that this sort of epilog will provide the greatest possible benefit to readers of this thread. Reading through 15 pages of debate is tedious at best.

[chala]

Originally Posted by goboatingnow

In many mains power systems, because the supply is fed trough transformers, local earths must be re-established.

What difference do you make between the above quoted transformers and one isolation transformer wired with multiple outlets.?

[chala]

Originally Posted by Fuss

It would be nice (but probably not possible) if we could now have a short summary of the acceptable scenarios.

At the present there is only one acceptable scenario.

Originally Posted by chala

to comply with the regulations in force

[pbiJim]

Originally Posted by chala

At the present there is only one acceptable scenario.

Quote:
Originally Posted by chala
to comply with the regulations in force



Non-compliance with regulations in a particular part of the world would be listed as a disadvantage in the epilog that I requested above. Depending on where one plans to sail, regional regulations may or may not matter.

[chala]

Originally Posted by pbiJim

I would also like to see this, now that so much has been hashed out.

We are discussing the merits of wiring a transformer as an isolation transformer with multiple outlets whose output is left “floating” ie. Two wires, no earthing of the output side of the transformer.

[chala]

Originally Posted by goboatingnow

Given chala that you insist RCD s are three wire when in fact only ever live and neutral are fed through it. An RCD does not require ground to operate . Merely that current flows to the power supply , via a or any path that does not contain the RCD. That path may or may not include earth

Dave

Yes and for that reason the power supply cannot be left floating with only two hots. " Merely that current flows to the power supply via a or any path that does not contain the RCD"

So we have as per above a live = one wire, a neutral = a second wire and a path = a third wire for the current to flows to the power supply.

[sailorchic34]

Originally Posted by chala

What difference do you make between the above quoted transformers and one isolation transformer wired with multiple outlets.?

In the US, the typical power company transformer serving residential single phase service has the secondary center tap reconnected to earth ground. So ground is referenced on both sides of the transformer and provides a ground loop path for conductance.

With the IT system like Jedi has, the secondary side is isolated from all ground paths. With a true floating IT, the current path is always between the two conductors and not conductor to ground. This greatly reduces shock hazard.

Its not perfect as it is still possible to get connected to each leg of the circuit through various faults as previously discussed. But overall, it practically eliminates leg to earth shock hazards on a boat. When installed correctly.

[sailorchic34]

Originally Posted by chala

Yes and for that reason the power supply cannot be left floating with only two hots. " Merely that current flows to the power supply via a or any path that does not contain the RCD"

So we have as per above a live = one wire, a neutral = a second wire and a path = a third wire for the current to flows to the power supply.

Actually with an IT, it's really just two wires that compete the circuit. Both ends have the same potential, so its not exactly correct to say to you have a hot, a neutral and ground.

I'm not saying this well, but the two wire carry no current or voltage unless the circuit is complete. You really have two hots at opposite phase to each other.