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Old 16-08-2013, 13:30   #31
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Re: Isolating Transformers, The Earth wire connection conundrum

BTW, taking the ABYC standards for non IT installs and comparing it to ISO 13297, I believe that the AC to DC connection and the binding of AC earth to the boats bonding systems actually contributes to poor AC safety

when you combine that with the lack , until recently of whole boat RCD ( and still RCD less supply pillars) , ABYC creates a whole series of local earths on the boat. This allows leakage currents, not faults currents upto the value of the breaker to flow into the underwater medium, in freshwater this is a series issue.

Yet this is actually countary to NEC practices that say that only one earth position should be established , essentially at the entry to the premises. This is specifically to avoid creating multiple earth fault paths and the dangers associated with it.

ISO 13297 on the other hand , once an RCD is installed requires no DC AC connection and the RCD does not require bonded underwater hardware. Hence on typical modern GRP boat , the AC will not cause a swimming hazzad ,as there is little chance of a fault path to seawater., and the issue of AC making DC hot, is dealt with by RCDs. equally even if leakage current gets established the presence of a RCD will trip once it gets to 30ma, whereas in the US theres nothing unto the fuse trip level to stop it.

No wonder swimmer shock and galvanic corrosion and brass/bronze debates are 'hot' on US boats, the code facilitates it.

dave
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Old 16-08-2013, 18:32   #32
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I thought ABYC standards were copyrighted and could not be reproduced freely.
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Old 16-08-2013, 18:56   #33
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Re: Isolating Transformers, The Earth wire connection conundrum

I think Greg raises a fairly serious issue in the example of the resistance of the ground circuit in his marina. I may be wrong but it appears that should there be a ground fault on any of the vessels in the marina the grounds in all vessels would become live.

I decided to float all the DC systems when I discovered the severity of hull electrolytic corrosion. I had been scraping of barnacles prior to scrubbing and re-antifouling and discovered that the scraping had removed spots of the epoxy paint and that this had caused corrosion concentration cells. I then went looking for the current source.

One of the current sources was the HF radio where the signal and chassis grounds are common-ed in both the radio and the ATU. This was fixed by removing the radio ground completely and putting a bank of capacitors on the signal ground in the ATU.

Isolating the engine from the hull proved fairly simple as there was only a single point of conduction left which was the gear shift and throttle control cables. I just isolated the entire panel from the hull with gaskets and insulating washers. The engine sits of polymer mounts and there is a polymer flex joint between gearbox and prop shaft.

The house system was isolated from the hull when I fixed the radio problem however isolating house and cranking systems is a little more problematic as the second house charging alternator needs to be insulated from the engine and I need to do this then run an earth return from alternator to house negative.

The reason I think all this has become necessary is because of the change over to ablative antifoul paints, when you do a lot of miles they ablate in a fairly short period of time compared with the old leaching antifouls so barnacles are more likely to become established and the old leaching product with their vinyl base tended to put another insulating layer onto the steel each time they were applied.

I suspect that steel boats would be better of with + to earth systems.
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Old 17-08-2013, 09:48   #34
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I think Greg raises a fairly serious issue in the example of the resistance of the ground circuit in his marina. I may be wrong but it appears that should there be a ground fault on any of the vessels in the marina the grounds in all vessels would become live.

I decided to float all the DC systems when I discovered the severity of hull electrolytic corrosion. I had been scraping of barnacles prior to scrubbing and re-antifouling and discovered that the scraping had removed spots of the epoxy paint and that this had caused corrosion concentration cells. I then went looking for the current source.

One of the current sources was the HF radio where the signal and chassis grounds are common-ed in both the radio and the ATU. This was fixed by removing the radio ground completely and putting a bank of capacitors on the signal ground in the ATU.

Isolating the engine from the hull proved fairly simple as there was only a single point of conduction left which was the gear shift and throttle control cables. I just isolated the entire panel from the hull with gaskets and insulating washers. The engine sits of polymer mounts and there is a polymer flex joint between gearbox and prop shaft.

The house system was isolated from the hull when I fixed the radio problem however isolating house and cranking systems is a little more problematic as the second house charging alternator needs to be insulated from the engine and I need to do this then run an earth return from alternator to house negative.

The reason I think all this has become necessary is because of the change over to ablative antifoul paints, when you do a lot of miles they ablate in a fairly short period of time compared with the old leaching antifouls so barnacles are more likely to become established and the old leaching product with their vinyl base tended to put another insulating layer onto the steel each time they were applied.

I suspect that steel boats would be better of with + to earth systems.
Interesting work. What have you done with the AC system.
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Old 17-08-2013, 14:59   #35
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Re: Isolating Transformers, The Earth wire connection conundrum

Dan: To state the obvious, yes all ABYC standards are copyrighted and are available for sale to members only. The copies that are spread around the internet are being given away illegally. Unfortunately the only legal way to get a copy is to spend a couple of hundred dollars to become a member and to buy the standards, which is reasonable for a professional marine electrician but OTT for the rest of us. It was recommended to me to join for just a year to buy the standards and then let it lapse (and presumably not keep current). That still seems excessive for people like me that built and maintain exactly one boat. Otherwise join the pirates - ARRRRGGGGH!

I do appreciate this thread - I have been wrestling with these issues for some time now. It seems to me that using my one ELCI to protect a short length of cable and then the internal shield in the transformer is wasteful and very unlikely to ever be needed. OTOH an ELCI at the distribution panel provides protection at the places it is likely to be needed, and for the inverter output as well (no genset in this little boat). And this is true, as Dave notes, as a direct result of the ABYC standard requiring a seawater ground even though the same standard would put the ELCI before the transformer and not provide this protection. Buying a second ELCI would cover all of the bases but seems like a bad use of $150. Thinking...

Edit: I should add that an ELCI at the input would be even less valuable if the NEC would require marinas to have ELCIs at the pedestal as is common in Europe. And it seems to me that the grandfathered marinas should be required to come up to code at some point...

Greg
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Old 17-08-2013, 18:55   #36
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Re: Isolating Transformers, The Earth wire connection conundrum

First a comment on the Standards thing. I agree with you fully on this subject Greg, I think they should be available to the non commercial public free of charge.

Having participated in this thread and the resulting pondering required to understand the subject matter I am inclining to the opinion that both DC and AC are probably better left floating. This tendency has been reinforced by the observation that the only AC appliances that even have an earth terminal in the plug are the microwave oven and some older power tools - not that many decades ago everything had an earth prong on the plug.

I have to confess that I do not have an earth leakage breaker on the vessel itself having burnt two of them out using gensets on the AC circuit and noting that every marina and slipyard I visited had them on the pedestals, it must be a requirement here.

I can control what happens on my boat. I cannot control what happens on other boats or the marina facilities. If someone on another vessel wrongly wires something and the earth system goes live because the marina wiring is poorly maintained it appears that a hazard is introduced to my vessel over which I have no control. This coupled with the improbability of me heating up lunch on the microwave whilst the boat is sinking and I am up to my knees in water inclines me to just leave things the nice simple way they are at the moment.
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Old 17-08-2013, 20:11   #37
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Re: Isolating Transformers, The Earth wire connection conundrum

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The ABYC docs are widely available on line
Please let me know where. I looked & did not find them available without paying dearly for them.
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Old 17-08-2013, 20:53   #38
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Re: Isolating Transformers, The Earth wire connection conundrum

I am not yet at the point of needing to make a decision so I'll punt for a bit more :-)

I have no intention of bonding the thru-hulls, as they are all located away from DC and far away from AC with no likely path for leakage. I also will have the new prop and shaft isolated when I install with a Drivesaver, and it will have a small shaft zinc (probably not needed). My plan is to replace the DynaPlate D-12 (seawater interface) with a stainless mount for a zinc anode; the Dynaplate did suffer modest damage from a badly wired marina in the UK (as did a previous prop). I will connect the AC secondary neutral and grounds together and will probably locate the ELCI there, but the isolation of AC ground from DC ground from seawater interface is still under consideration - I might just run grounding cables from the seawater interface to the AC secondary and the DC common ground point (bus bar) and not make the connections. I will also be considering buying a second ELCI for the input wiring, but that may be a hard sell as it offers so little protection.

Still thinking...

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Old 18-08-2013, 01:35   #39
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Re: Isolating Transformers, The Earth wire connection conundrum

My engine is mounted on Polyflex engine mounts and these insulate the engine fr5om the engine beds. There is also a Polyflex coupling between the gearbox output flange and the flange on the prop shaft which insulates the engine/gearbox from the prop shaft. The Polyflex coupling is a polymer disk one side of which is clamped to the gearbox flange and the other side is clamped to the prop shaft flange there is no metal to metal contact in either the Polyflex coupling or the Polyflex engine mounts.

Regards Raymond.
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Old 18-08-2013, 17:43   #40
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Re: Isolating Transformers, The Earth wire connection conundrum

I picked up a ways back that your boat is steel. IIRC S/Y Jedi is aluminum. If I had a metal hull I would almost certainly isolate all AC and DC electrical systems from the hull, and particularly if it is aluminum. But I would also take great care that it stays isolated through the wear and tear of years. My fiberglass hull isn't likely to see damage as a result of stray corrosion, but metal boats can be damaged badly by it. And a metal hull would make a great conductor for any potential electro-shock drowning. So insulate, and make sure it stays that way.

Greg
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Old 18-08-2013, 17:49   #41
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Please let me know where. I looked & did not find them available without paying dearly for them.
As was noted , illegal copies are widely distributed

Dave
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Old 18-08-2013, 17:54   #42
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CarinaPDX. It always failed me that ABYC had to design some wierd spec and reinvent the wheel , there was a mention of it on another post. Here in Europe we use off the shelf , but it in the local hardware or electrical store , standard 30ma trips , about 40 pounds /50 euros. They work fine.

Yes I suppose the input RCD in an isolating transformer is somewhat underused. But it does provide a safety protection if that shore hot ever touches anything on the boat , a problem the fuses will not detect.

Dave
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Old 18-08-2013, 18:37   #43
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Re: Isolating Transformers, The Earth wire connection conundrum

On the subject of electro-shock drowning, I assume that would require a swimmer to be a better conductor than the water around him. Does anyone know of a study that has documented the difference in resistance between these two?

It seems strange to me intuitively that a swimmer 10 feet away from a poorly wired boat would have a problem. I can certainly see that a person in the water touching a boat with bad wiring could have a problem though.

Does anyone have more info on this sort of thing?
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Old 18-08-2013, 19:00   #44
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Re: Isolating Transformers, The Earth wire connection conundrum

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......IIRC S/Y Jedi is aluminum.
Jedi is GRP.
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Old 18-08-2013, 19:35   #45
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Re: Isolating Transformers, The Earth wire connection conundrum

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As was noted , illegal copies are widely distributed

Dave
After much googling, it appears as though ABYC is starting to get on board with Europe when it comes to ground faults.

THE AMERICAN BOAT AND YACHT COUNCIL RESPONDS TO ELECTRIC ... PDF - Pdfsdb.com

Heaven forbid, the public should be informed.

If you have an hour & a half to kill, this might be an interesting webinar -
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