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Old 25-10-2013, 02:03   #136
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Re: Isolating Transformers, The Earth wire connection conundrum

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Originally Posted by sailorchic34 View Post
To add a earth to a IT would defeat part of the safety feature that the IT gives. Its Isolated power, not connected to shore or an earth loop, for goodness sake.
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That is one of the main reasons to have a isolation transformer after all.
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Normally an isolating transformer used for personal safety consist of one isolating transformer and only one outlet then your moon rock theory may hold. One isolating transformer used to supply a complete electrical installation does not offer personal safety.
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Just to clarify or maybe confuse the issue more.
Please before trying to confuse the issue more try instead to make the difference between a foot and a head.
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Old 25-10-2013, 02:23   #137
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Re: Isolating Transformers, The Earth wire connection conundrum

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You say they use these circuits in hospital
I suspect that Gobo got the same problem than Sa34
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Old 25-10-2013, 02:24   #138
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Re: Isolating Transformers, The Earth wire connection conundrum

Response to Flying cloud.
I for one will not tell you how to fix this problem, you know plenty. My issue is still with this conundrum thingo.
Ship regs are far tighter than shore regs anywhere. If Classification rules do not provide the safety required then usually statutory (shipstate) will.
On ship its entirely satisfactory for a potential fault to come into existence before you do something about it, and you attend to it soon after.
Class authorities evolved a system that best works for them, they are pretty consistant around the world.
The point is on ship you have means of determining such a state exists, and its not hard to implement, I’ve stated it on previous post re: earth lamps.
For others benefit, there are the usual suspects, if not, keep isolating till you find it. Once found, fix it or put a danger tag on it and make it unavailable till you get the parts/replacement.
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Old 25-10-2013, 02:41   #139
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Re: Isolating Transformers, The Earth wire connection conundrum

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Personnally I would go the Isolated Transformer way, but there are some of us who insist on RCD devices and lots of work place safety requirements mandate RCD devices to even work on a yacht.
Ocean, what does "Au" stand for in “Melbourne, Au”?
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Old 25-10-2013, 02:49   #140
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I still think most miss my point. In the USA we work against "potential fault" because potentials seem to happen and then someone loses a life.

I have a boat(customer) right now that has a floating IT/Step-up with a Euro 230v range. When plugged into shore all seems to work well, no tingler.

As soon as the shore side is disconnected, and the range is powered by the Diesel-Gen going thru the same IT/Step-Up, touching any part of the range/cooker it's a tingler.

So we have a fault, ie double fault. It's the only load on that circuit, it's wired correctly.

We have a potential that is an actual working fault. go figger

Lloyd
Ground loop internal to the boat. Furthermore the it transforner should not be in front of the generator. iTs should be exclusively shore power feeds as its regarded as a power source. Also such a series connection almost guarantees a ground loop. Bad idea

Dave
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Old 25-10-2013, 02:50   #141
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I suspect that Gobo got the same problem than Sa34
Huh. I'm currently looking at one right this minute in a hospital

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Old 25-10-2013, 02:54   #142
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Well Chala before you got accusing a reputable person of confusion you should examine this snippet of yours
"
Originally Posted by chala
Normally an isolating transformer used for personal safety consist of one isolating transformer and only one outlet then your moon rock theory may hold. One isolating transformer used to supply a complete electrical installation does not offer personal safety."

Since a boats IT is a single item , its exactly the same as a personal safety issue. Rather then just throwing out unsupported statements you could cogently argue your viewpoint technically

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Old 25-10-2013, 05:24   #143
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Re: Isolating Transformers, The Earth wire connection conundrum

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Well Chala
Gobo try harder.
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Old 25-10-2013, 06:19   #144
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Re: Isolating Transformers, The Earth wire connection conundrum

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I have been writing to use gfci outlets to prevent any of the scenarios incl. the very unlikely, since way back in the thread. The only ones recognizing it are Dave and Dan, who obviously are engineers too. The rest still needs the quarter to fall, or are ignoring it because it would kill their argument they love to repeat
This will require a bonding conductor connected to one of the terminals on the output side of the isolating transformer.

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I can't bring up the incentive to discuss this silly repeat of having to ground a leg from a transformer or genset and live with a neutral. I will only say that this is the result of ignorance; this has been discussed to death too often now and many boats are 100% safe without a neutral and thus a floating system with two hot's.
In other word this new wiring could be described as having a one Active (Hot1), a Neutral, and an Earth wire.
And if so this will be the result of ignorance. Welcome to the team.
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Old 25-10-2013, 06:49   #145
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This will require a bonding conductor connected to one of the terminals on the output side of the isolating transformer. In other word this new wiring could be described as having a one Active (Hot1), a Neutral, and an Earth wire. And if so this will be the result of ignorance. Welcome to the team.
Omg Chala. You really have no clue!
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Old 25-10-2013, 07:28   #146
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Re: Isolating Transformers, The Earth wire connection conundrum

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Ya know....you guys are actually agreeing....
On what?
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Old 25-10-2013, 08:11   #147
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Re: Isolating Transformers, The Earth wire connection conundrum

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Omg Chala. You really have no clue!
So you got the clue.
Here are two GFCI as you may notice each one have 3 wires. How do you connect them to yours two wires floating wiring?
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Old 25-10-2013, 08:46   #148
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Re: Isolating Transformers, The Earth wire connection conundrum

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Its clear that (3) is the preferred ( ABYC) US approach, yet such an approach adds earth as a fault path. ( note not a fault path TO earth). with this system if the secondary HOT ( L) touches anything on the boat and the user touches that, then a fault path to the neutral side of the transformer exists via seawater which causes a shock. ( this assumes the 'thing' is not connected to the protective wire).

What I dont understand is , by deliberately defeating the isolation it reintroduces the swimmer in freshwater risk, as fault currents can now flow through seawater , ie out of one underwater fiting and back through another, especially if the protective wire is poor made or connected.

ABYC, does not like (1) above and to be fair , several other code bodies do not like floating 1:1 POWER transformers. Why?

(b) A rather strange concern ( as Calder as described) of the floating HOT touching an appliance, and raising the potential of that appliance unbeknownst to teh occupant, then a subsequent fault on the other HOT causes the occupant to be inserted into the circuit.

Now this is rather a bizarre claim, and seems to completely ignore two things
(a) A RCD on the secondary side covers this

Which in reality is right.
For an Electrical Engineer you really surprise me. You are supposed to know and understand the above. Not have to ask a forum of cruisers.

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In a true floating system,
, the rcd will do little.
In a full floating system RCDS do virtually nothing
Gobo have you made up your mind, do little or do virtually nothing?

Whatever the answer, you seem to have found a reason for that “ bizarre claim”.
Maybe the ABYC knew that a RCD would do little or virtually nothing.
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Old 25-10-2013, 09:35   #149
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Re: Isolating Transformers, The Earth wire connection conundrum

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If a contentious owner has multiple such crummy appliances and they are still extremely worried about safety then individual GFI circuits for each appliance will solve this problem.
Any appliance that requires to be earthed may leak or leak continuously. If that appliance cannot leak then the potential of that appliance will raise and so will anything else that is conductive and in contact with the appliance.
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(b) A rather strange concern ( as Calder as described) of the floating HOT touching an appliance, and raising the potential of that appliance unbeknownst to teh occupant, then a subsequent fault on the other HOT causes the occupant to be inserted into the circuit.
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Old 25-10-2013, 10:12   #150
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Re: Isolating Transformers, The Earth wire connection conundrum

The thing about these threads that I'm sure is very frustrating to many readers is who do you believe? Anybody can say what they like on this forum. However, as I like to remind the junior engineers in my department, though you may be entitled to your own opinions, you're not entitled to your own facts! To Chala, you are disagreeing with a number of electrical engineers with quite a bit of experience in the field. You also make statements which clearly show your lack of understanding. Perhaps it's just terminology differences, but if so, you need to fix your terminology. Some of us have designed power systems in safety critical medical applications (myself for one). Others just seem to have opinions based on what they've seen or based on their own misunderstanding of the subject. Dave (GBN), Jedi, and myself all see the relative merits of a totally isolated AC power system. ABYC is concerned with a much broader audience than electrical engineers. Their standards must reflect that. They must prescribe techniques that provide the safest approach for the broadest audience. This implies simple. In absolute terms, the totally isolated approach is the safest. In broader terms, some analysis may be required to determine that a potential problem exists or what to do about it. ABYC cannot prescribe analysis. They can only prescribe process. For example, if an isolated system yields "tingling" when touched, it's not really isolated (completely). There may be a problem with the transformer, but it's likely a wiring error. There is a leakage path somewhere that is going to require some analysis to nail down. That analysis is difficult to do via internet forum, and even more so via prescribed process. I believe that is the reasoning behind ABYC's standard. As the equipment and methods gain acceptance and standardization, I believe ABYC will come around.

As a follow on discussion, some of us are simply unwilling to add 60 lb. chunk of iron to our boats that is only useful in the planned somewhat rare occasion we are on dock power. For us, I think the best, safest method is whole boat RCD, GFCI's on every branch circuit, no ground to seawater. Opinions?
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