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Old 12-08-2013, 13:09   #76
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Re: Heads Up - Victron Isolation Transformer

Place all on boat AC devices off. What is the hull potential with shore power physically plugged in and shore power physically disconnected? How about plugged in with shore breaker on shore breaker off? Any change in potential implicates a transformer problem or possibly that the transformer installation was as a polarization device. If so then you still would need a galvanic isolator.

No potential change rules out the transformer as a zinc degrade trouble source.

By the way what is a "prop cage" and why does it involve a zinc?

Charles
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Old 12-08-2013, 17:10   #77
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I would make sure they wired ground correctly. With everthing diaconnected and switched OFF, you can use an Ohm meter to check this quickly:

between shore power inlet ground pin and isolation transformer housing, there should be NO conductivity. I bet the tech installed a ground jumper there which voids the isolation aspect of the transformer. The Victron's come with that jumper for when you haul out and are on the hard. It should be removed while in the water.
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Old 12-08-2013, 17:29   #78
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Originally Posted by s/v Jedi View Post
I would make sure they wired ground correctly. With everthing diaconnected and switched OFF, you can use an Ohm meter to check this quickly:

between shore power inlet ground pin and isolation transformer housing, there should be NO conductivity. I bet the tech installed a ground jumper there which voids the isolation aspect of the transformer. The Victron's come with that jumper for when you haul out and are on the hard. It should be removed while in the water.
I agree , sounds like the " certified marine technician" screwed up the install

Dave
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Old 12-08-2013, 17:43   #79
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Re: Heads Up - Victron Isolation Transformer

If you mean to say the transformer installation should have no safety green continuity from shore power to the AC devices on the boat that will surely isolate your boat from you neighbor's galvanic sins.

However, if you install the transformer in that manner you will also vastly increase the shock hazard to crew and swimmers. Isolation transformers are not intended to protect from galvanic problems at the expense of safety - not in hospitals boats or anyplace else these devices get used.

As to the question at hand: Can an isolation transformer contribute/cause accelerated zinc loss? Testing hull potential as above noted will tell you if the transformer might be the culprit and at least you will know if any shore power conductor is in play.

Charles
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Old 12-08-2013, 17:48   #80
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Originally Posted by Chas Erwin View Post
If you mean to say the transformer installation should have no safety green continuity from shore power to the AC devices on the boat that will surely isolate your boat from you neighbor's galvanic sins.

However, if you install the transformer in that manner you will also vastly increase the shock hazard to crew and swimmers. Isolation transformers are not intended to protect from galvanic problems at the expense of safety - not in hospitals boats or anyplace else these devices get used.

As to the question at hand: Can an isolation transformer contribute/cause accelerated zinc loss? Testing hull potential as above noted will tell you if the transformer might be the culprit and at least you will know if any shore power conductor is in play.

Charles
What. This is nonsense. You do not extend the shore power AC protective earth through the boat in a isolating transformer installation. Its not in the circuit and does nothing. That's the whole point of such a transformer. Its a generator source AC protective earth should return to designated neutral side of the transformer.

Isolating transformers , properly installed , provide both galvanic isolation and on board safety.

I fail to see " hull potential" as having anything to do with this. In my view the grounds are incorrectly wired and the isolation effect was bypassed.

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Old 12-08-2013, 18:06   #81
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Re: Heads Up - Victron Isolation Transformer

My point is that it to sever (terminate safety green from the secondary side of the transformer) presents a shock hazard to people on the boat. An isolation transformer system and polarization transformer system have very specific meanings.

Before you get all defensive please read Rifkin "Isolation or Polarization; Which is the Safest Transformer Installation?"

Changed my mind - and I hope you will seriously consider what he has to say too.

As to the zinc loss complained of measuring hull potential in the steps I noted will tell you whether the source of zinc erosion is from your boat or a neighbor, or maybe the marina.

Charles
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Old 12-08-2013, 18:22   #82
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Originally Posted by Chas Erwin View Post
My point is that it to sever (terminate safety green from the secondary side of the transformer) presents a shock hazard to people on the boat. An isolation transformer system and polarization transformer system have very specific meanings.

Before you get all defensive please read Rifkin "Isolation or Polarization; Which is the Safest Transformer Installation?"

Changed my mind - and I hope you will seriously consider what he has to say too.

As to the zinc loss complained of measuring hull potential in the steps I noted will tell you whether the source of zinc erosion is from your boat or a neighbor, or maybe the marina.

Charles
Explain how it provides a shock hazard ?

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Old 12-08-2013, 18:31   #83
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Re: Heads Up - Victron Isolation Transformer

Rifkin's article answers that question plainly and clearly.

Go to Quality Marine Services, LLC. Choose documents, then Item 5.

Charles
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Old 12-08-2013, 18:38   #84
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Re: Heads Up - Victron Isolation Transformer

Friends - thanks very much for your input on my question regarding the Isolation Transformer (IT) and Galvanic corrosion. I suspected that there was improper grounding of the IT. I think that the best course would be to remove the entire Victron unit since I don't really need it in Maine where I rarely tie up to a dock and almost never use shore power.

Chas - a "prop cage" is a metal cage that surrounds the lateral aspects of the prop that attaches to the deadwood. It prevents lines from lobster traps from tangling in my 3-blade MAX-PROP. Many lobster boats have them also.
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Old 12-08-2013, 18:45   #85
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Originally Posted by Chas Erwin View Post
Rifkin's article answers that question plainly and clearly.

Go to Quality Marine Services, LLC. Choose documents, then Item 5.

Charles
Sorry to say but what you say is genuine BS. A marine isolation transformer install method is NOT a matter of opinion. Codes are in place to protect people from these kind of mishaps. Typical to read that Chas will not accept anything but his version. Shame if somebody does because of it.
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Old 12-08-2013, 18:46   #86
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Originally Posted by kellyp08 View Post
Friends - thanks very much for your input on my question regarding the Isolation Transformer (IT) and Galvanic corrosion. I suspected that there was improper grounding of the IT. I think that the best course would be to remove the entire Victron unit since I don't really need it in Maine where I rarely tie up to a dock and almost never use shore power.

Chas - a "prop cage" is a metal cage that surrounds the lateral aspects of the prop that attaches to the deadwood. It prevents lines from lobster traps from tangling in my 3-blade MAX-PROP. Many lobster boats have them also.
You should not remove it. Correct the error and what you have is a safety device second to none for the boat and her crew whenever connected to shore power.
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Old 12-08-2013, 18:47   #87
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Dave Rifkins article is typical of the sclerotic issues around combining domestic standards and boat standards and as a ABYC certified, he's arguing against himself.

In order to justify the continuous ground argument , he manufacturers a failure mode and then argues for its protection, ie the short between secondary and shield.

Furthermore his assumptions are based on US practice of bonded underwater to AC earth. A practice that is not followed in say Europe.

His solution conveniently ignores using RCD devices which on the output of the transformer will provide protection from an obscure secondary to shield fault.

European practice is to use RCDs , not bond AC earth to DC negative , not bond underwater fittings together on GRP boats , where isolating traffos are used the boat AC protective never connects to shore earth

Furthermore Dave Rifken
"
Would you intentionally go around your own home and selectively sever the green grounding connections on receptacles and applianc- es? Of course not! The same argument applies when the grounding connection is severed on a boat using an Isolation Transformer System!
"

Perhaps he might vist a UK construction site , where 110 vac isolating transformers are mandatory , the earth is not continuous , or perhaps he's never heard of double isolated tools etc.

His article seeks to take one case and generalise. Every system has fault potential, you cannot eliminate them

For example , as a alternative , run Rifkens case , where the shore AC protective earth , goes hot. Now his solution deliberately compromises the security provided by the transformer. Every system can be faulted.


A proper high quality transformer , should provide complete isolation , AC protective earth should be local to its own generator. It should not be connected through to the shore earth ( this is ABYC code) . This allows the transformer to do its job , a d as nick says provide a safety system bar none
Dave
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Old 12-08-2013, 19:17   #88
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Re: Heads Up - Victron Isolation Transformer

Well it is clear then that the only difference here is that safety green continuity (in a transformer case) represents solely and exclusively a risk of galvanic mischief sourced to a neighbor boat. In all other aspects both systems offer an identical and superior level of safety in cases of AC faults.

So why are tempers rising when all we are concerned about is stemming some hypothetical galvanic threat?
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Old 12-08-2013, 19:47   #89
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Re: Heads Up - Victron Isolation Transformer

Quote:
Originally Posted by Chas Erwin View Post
Well it is clear then that the only difference here is that safety green continuity (in a transformer case) represents solely and exclusively a risk of galvanic mischief sourced to a neighbor boat. In all other aspects both systems offer an identical and superior level of safety in cases of AC faults.

So why are tempers rising when all we are concerned about is stemming some hypothetical galvanic threat?
What's clear is that you don't understand electric current flow or galvanic issues.
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Old 12-08-2013, 19:47   #90
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Originally Posted by Chas Erwin View Post
Well it is clear then that the only difference here is that safety green continuity (in a transformer case) represents solely and exclusively a risk of galvanic mischief sourced to a neighbor boat. In all other aspects both systems offer an identical and superior level of safety in cases of AC faults.

So why are tempers rising when all we are concerned about is stemming some hypothetical galvanic threat?
Fundamentally the purpose of an isolating transformer is to create a floating AC supply. Running the shore protective earth , via secondary neutral and onwards into the boat compromises that situation as it again references the output of the transformer to earth and exposes all onboard to the usual panoply of earth referenced AC faults. It makes no sense.

Its not about galvanic corrosion , its about safety and that proposal compromises general safety in order to protect against a single specific and obscure fault.

Dave
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