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Fitting a galvanic isolator


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On the face of it, this seems a simple matter. Locate the wire from the shore power socket on the stern, break the earth, insert the isolator into the break, screw to the wall, make it all tidy.

 

Am I missing anything? Does it make a difference what isolator I buy?

 

Thanks.

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19 minutes ago, Galilee said:

On the face of it, this seems a simple matter. Locate the wire from the shore power socket on the stern, break the earth, insert the isolator into the break, screw to the wall, make it all tidy.

 

Am I missing anything? Does it make a difference what isolator I buy?

 

Thanks.

Yes the installation concept is correct.

 

yes it does make a big difference what isolator you buy, primarily on 2 counts:

 

1/ if you buy an isolator with no indicators (meter, LEDs) you have no idea whether or not the device is going into conduction and your hull is rotting away, due to a rogue voltage on the shore earth. Remember that all GIs just isolate a volt or two of voltage difference between hull and shore earth, beyond that they conduct. Also, with a meter, a slight deflection of the needle when you plug the shore power in is reassurance that it’s doing it’s job and not failed short circuit.

 

2/ There is no legally binding standard for GIs, but there is an international standard from ABYC. This covered two main points of safety, one that the device won’t fail open circuit (thus rendering your boat un-earthed) and two that the diodes can take the peak current from a short circuit for the brief time before the breaker trips, without damage. That current, from a normal supply rated at 16A, can be thousands of amps for the instant before the breaker trips.

 

Lesser GIs will damage themselves following such a short circuit, either leaving the boat unprotected against galvanic currents, or isolated from shore earth (dangerous).

 

Which brings up an installation point, best to install such that the integrity of the GI can easily be checked using a battery / bulb / voltmeter (ie readily accessible). GI should always be checked for damage following a breaker trip.

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7 minutes ago, Boater Sam said:

There is however a school of thought that the inclusion of an LED icompremises the effectiveness somewhat.  It has to draw a current even though very small to illuminate

 

The LED only illuminates when the diodes are on the point of conduction. If everything is hunky dory they are not illuminated. Your point is however valid for a meter, but the current is a few micro amps.

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5 minutes ago, Galilee said:

Perfect, thanks for taking the time to write such an informative answer.

You’ll know the instant you look at an ABYC compliant GI by the difference in price from the non-compliant ones. 

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8 minutes ago, WotEver said:

You’ll know the instant you look at an ABYC compliant GI by the difference in price from the non-compliant ones. 

Yeah, I was looking at a Victron one for just over £200, but now I see it has no indicators

 

Hmmm, and there are Safeshore ones for ~£100 that do have an LED.

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41 minutes ago, Galilee said:

Yeah, I was looking at a Victron one for just over £200, but now I see it has no indicators

 

Hmmm, and there are Safeshore ones for ~£100 that do have an LED.

Safe shore ones aren’t ABYC compliant as far as I can tell. However I am not saying you should definitely get an ABYC compliant one - it depends on how you view risk vs cost. You question was after all about the differences, not about a recommendation. If you have a non-ABYC compliant GI, as many people do, the probability of coming unstuck is very small, especially if you check the integrity of the GI following any breaker trip event.

 

If it is of any help, this is the one we have, which although slightly weasily-worded, does at least seem to meet the ABYC standard even if not specifically tested and approved by them: https://aquafax.co.uk/product/8-40990-galvanic-current-isolator-16a-with-indicator

 

I like that it has a meter, but as per the previous posts this does mean a tiny current will flow through the device whenever the meter is deflected slightly. But I like it that I see a very slight deflection when I plug into shore power at the marina, means it’s working! When we recently plugged in elsewhere (Liverpool docks) the meter deflected quite a bit further, though not into the danger zone. So there is quite a variation out there in terms of shore power earth voltage.


Another minor point is the inclusion of a capacitor across the diodes, this allows AC ripple /spikes from electronic power supplies etc, to pass freely without bringing the diodes to momentary conduction. IMO this is less relevant these days because electronic power supplies (phone chargers etc) tend not to have an earth connection. Earlier devices tended to use the earth to dump the switching spikes from the electronics.

 

So capacitors are good, but not vital.

Edited by nicknorman
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47 minutes ago, Galilee said:

Yeah, I was looking at a Victron one for just over £200, but now I see it has no indicators

 

Hmmm, and there are Safeshore ones for ~£100 that do have an LED.

Yes, if a GI complies with the ABYC specs then it doesn’t require indicators for the obvious reason that it’s designed to fail safe. It’s still necessary to check it on occasion though, just for peace of mind. 
 

As you observe, Safeshore GIs which don’t comply with the ABYC spec are much, much cheaper than ones which do, such as this Mastervolt offering:

https://www.waveinn.com/nautical-fishing/mastervolt-prosafe-fs-60/136411844

 

 

Edited by WotEver
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4 minutes ago, WotEver said:

Yes, if a GI complies with the ABYC specs then it doesn’t require indicators for the obvious reason that it’s designed to fail safe. It’s still necessary to check it on occasion though, just for peace of mind. 
 

As you observe, Safeshore GIs which don’t comply with the ABYC spec are much, much cheaper than ones which do, such as this Mastervolt offering:

https://www.waveinn.com/nautical-fishing/mastervolt-prosafe-fs-60/136411844

 

I still think an indicator is a good idea. Without an indicator, how do you know if you’ve plugged into a rogue shore power system and the GI’s threshold voltage has been exceeded, with you boat corroding away as a consequence?

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38 minutes ago, nicknorman said:

I still think an indicator is a good idea. Without an indicator, how do you know if you’ve plugged into a rogue shore power system and the GI’s threshold voltage has been exceeded, with you boat corroding away as a consequence?

I don’t disagree. But I was merely pointing out that the ABYC spec removed the indicator requirement some time ago. 

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3 hours ago, Galilee said:

On the face of it, this seems a simple matter. Locate the wire from the shore power socket on the stern, break the earth, insert the isolator into the break, screw to the wall, make it all tidy.

 

Am I missing anything? Does it make a difference what isolator I buy?

 

Thanks.

You missed out connecting the earth on the "boat" side of the GI to the boat hull. What, if any inverter do you have? Does it do auto switch over between shore power and inverter supplied mains? You may have to connect that to boat earth too to ensure there is a functioning earth under all circumstances that ensures the hull doesn't go live. Depends.

Jen

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22 minutes ago, Jen-in-Wellies said:

You missed out connecting the earth on the "boat" side of the GI to the boat hull. What, if any inverter do you have? Does it do auto switch over between shore power and inverter supplied mains? You may have to connect that to boat earth too to ensure there is a functioning earth under all circumstances that ensures the hull doesn't go live. Depends.

Jen

All those things should already be in place and don’t form part of installing a GI into an existing ac boat system with shore power. No harm in checking though.

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2 hours ago, nicknorman said:

 

If it is of any help, this is the one we have, which although slightly weasily-worded, does at least seem to meet the ABYC standard even if not specifically tested and approved by them: https://aquafax.co.uk/product/8-40990-galvanic-current-isolator-16a-with-indicator

I also have this unit fitted and, like you, find the meter reassuring. What is it you think is weasily worded Nick?  The link says: " Designed, manufacturered and tested to meet ABYC. A28 standard."  Is there something elsewhere to suggest this isnt right? 

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8 minutes ago, Alan de Enfield said:

"Tested to" not "Tested by" or "Approved by"

 

Marketing words for we have tested it in house and we say it meets the requirements.

Ah, I see, thanks. Well, let's hope they're better at building and testing electronic kit than they are at spelling manufactured!

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There is one GI that I can think of that is ABYC Compliant and has an indicator.  A snag with it that may not suit all installations is that it is an analogue meter fixed on the front of the device.

 

https://aquafax.co.uk/product/8-40990-galvanic-current-isolator-16a-with-indicator

 

There is a 32A version too.

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3 hours ago, nicknorman said:

 

2/ There is no legally binding standard for GIs, but there is an international standard from ABYC. This covered two main points of safety, one that the device won’t fail open circuit (thus rendering your boat un-earthed) and two that the diodes can take the peak current from a short circuit for the brief time before the breaker trips, without damage. That current, from a normal supply rated at 16A, can be thousands of amps for the instant before the breaker trips.

 

I have been having this discussion on Facebook. 

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1 minute ago, churchward said:

There is one GI that I can think of that is ABYC Compliant and has an indicator.  A snag with it that may not suit all installations is that it is an analogue meter fixed on the front of the device.

 

https://aquafax.co.uk/product/8-40990-galvanic-current-isolator-16a-with-indicator

 

There is a 32A version too.

That's the very one we're talking about above.  :)

 

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23 minutes ago, Alan de Enfield said:

"Tested to" not "Tested by" or "Approved by"

 

Marketing words for we have tested it in house and we say it meets the requirements.

The vast majority of manufactured products you can buy are self-certified by the manufacturer as meeting the relevant standard.  The design and manufacturing may be carried out under an independently audited quality management system, but that won't check the product compliance directly.

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1 minute ago, David Mack said:

The vast majority of manufactured products you can buy are self-certified by the manufacturer as meeting the relevant standard.  The design and manufacturing may be carried out under an independently audited quality management system, but that won't check the product compliance directly.

I worked in an industry where a product had to be submitted for independent testing (such as MilSpec, Lloyds, DNV etc) once it was approved then you could state 'approved by' but were not expected to submit every individual item manufactured for approval.

 

Following the Falklands and the Sir Galahad fire (where sailors were trapped in the boat and unable to escape due to cables falling and blocking the walkways and more were killed by smoke than the actual explosion) I was involved in developing a new range of cable fixings that had to withstand the impact / explosion of an Exocet missile. We had to have full independent testing and approval of its ability with withstand the G-Forces and the resulting fire and temperatures.

Before the MOD would accept the product we needed the independent test certificates  and Lloyds approvals.

 

I subsequently spent some time at BAE Barrow working on the introduction of the fixings for the Submarines, and at Glasgow working on the Type 45 Destroyers.

 

Cable ties are quite important little things !!!

 

ISO 9000 etc approval made sure your processes were consistent (not necessarily consistently good) so having your 1st production parts independently approved, and then applying ISO9000 should have meant that every product was in compliance.

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4 minutes ago, Alan de Enfield said:

Following the Falklands and the Sir Galahad fire (where sailors were trapped in the boat and unable to escape due to cables falling and blocking the walkways and more were killed by smoke than the actual explosion) I was involved in developing a new range of cable fixings that had to withstand the impact / explosion of an Exocet missile. We had to have full independent testing and approval of its ability with withstand the G-Forces and the resulting fire and temperatures.

Before the MOD would accept the product we needed the independent test certificates  and Lloyds approvals.

 

I subsequently spent some time at BAE Barrow working on the introduction of the fixings for the Submarines, and at Glasgow working on the Type 45 Destroyers.

Thank you for that. We sailors were aware of such many such developments post 1982 and appreciated the difference those efforts made to our safety. :)

 

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