Galvanic Isolators

[jonk]

Reading the discussions on bottom blacking and anodes I am coming to the conclusion that no-one REALLY KNOWS and has convincing proof, which is better/works best. So in light of that does anyone know, or have a convincing reason, whether a galvanic isolator will 100% protect a boat from corrosion caused by the attachment of a landline?

Thanks,

John

Edited February 21, 2011 by jonk

[DeanS]

Reading the discussions on bottom blacking and anodes I am coming to the conclusion that no-one REALLY KNOWS and has convincing proof, which is better/works best. So in light of that does anyone know, or have a convincing reason, whether a galvanic isolator will 100% protect a boat from corrosion caused by the attachment of a landline?

Thanks,

John

 

Hi John.

Some say it's better to have an isolation transformer. It also depends how the shoreline earth is connected...and how your boat earth is connected. Some say that if your 220V wiring on your boat is completely isolated from your boat, then it wouldn't matter, but others say that the canal water is a conductor and when you park next to someone who is connected to shorepower, your boat and their boat get charged...I even heard some people put an earth stake into the ground ...in short..I have no idea, but being a newbie myself, If I was to be connected for a long time, I guess I would get one...

[Gibbo]

Reading the discussions on bottom blacking and anodes I am coming to the conclusion that no-one REALLY KNOWS

 

Yeah they do. You're just listening to the ones who don't

 

and has convincing proof, which is better/works best. So in light of that does anyone know, or have a convincing reason, whether a galvanic isolator will 100% protect a boat from corrosion caused by the attachment of a landline?

Thanks,

John

 

Full blacking is better than partial blacking which is better than no blacking. This cannot be argued against. Though no doubt someone will try

 

An isolation transformer is better than a GI which in turn is better than nothing. This cannot be argued against.

 

Anodes is better than no anodes.

 

No, a GI will not 100% protect a boat from corrosion caused by the attachment of a landline. But a correctly installed isolation transformer will.

[Keeping Up]

Reading the discussions on bottom blacking and anodes I am coming to the conclusion that no-one REALLY KNOWS and has convincing proof, which is better/works best. So in light of that does anyone know, or have a convincing reason, whether a galvanic isolator will 100% protect a boat from corrosion caused by the attachment of a landline?

Thanks,

John

 

Probably nobody knows. It also depends what you mean by 100%.

 

Some boats but probably not all boats, in some circumstances but probably not all circumstances, will be protected 100%. In fact probably most boats in most circumstances will be protected 100% - probably.

 

There are no absolutes, it's a matter of balancing risk against cost. As an old boss of mine once splendidly said at a Board Meeting when asked if e could guarantee that his new marketing campaign would be successful, "If you want a guarantee, go buy yourself a toaster"

[churchward]

Yeah they do. You're just listening to the ones who don't

 

 

 

Full blacking is better than partial blacking which is better than no blacking. This cannot be argued against. Though no doubt someone will try

 

An isolation transformer is better than a GI which in turn is better than nothing. This cannot be argued against.

 

Anodes is better than no anodes.

 

No, a GI will not 100% protect a boat from corrosion caused by the attachment of a landline. But a correctly installed isolation transformer will.

I think Gibbo says it all really.

 

My take is that going by cost V risk etc. GI is good for minimal or moderate use of a landline and a transformer is worth considering if you use a landline a lot or permanently or if you use a lot of devices that practice current dumping (or whatever the technical term is) through the earth connection. But again to agree with Gibbo the only way to be 100% sure is to have an isolation transformer. A GI will protect the boat in most circumstances but in some cases may fail. There are also GIs that are better than others in terms of protection against current flow so worth taking advice and shopping around of going the GI route.

 

On my boat I have a GI as I don't use the landline that much so most of the time the hull is totally disconnected so it seems a lot of money to spend on an Iso transformer for the times I am connected.

[jonk]

Yeah they do. You're just listening to the ones who don't

 

 

 

Full blacking is better than partial blacking which is better than no blacking. This cannot be argued against. Though no doubt someone will try

 

An isolation transformer is better than a GI which in turn is better than nothing. This cannot be argued against.

 

Anodes is better than no anodes.

 

No, a GI will not 100% protect a boat from corrosion caused by the attachment of a landline. But a correctly installed isolation transformer will.

 

Thanks for that! I am sure you are correct!

I had not come across an isolation transformer before - a new bit of information to explore!

John

 

Thanks for the replies everyone, must say they confirm what I thought, which is nice!

John

[Frankieboy]

Heres probably a numpty question then.....

Supposing I dont use shore power that often but was thinking about an isolation transformer. Where would I get one from, what size (if there is a size) do I need, and roughly how many coins would it set me back?

If it helps, theres hardly any 240v appliances on boat, no washing machine or other "heavy duty" power use.

[boots]

I have one of these:-

 

http://www.airlinktransformers.com/article/waterways-article.html

 

http://www.airlinktransformers.com/transformer/wp3231-weatherproof-transformer.asp

 

Martin

[WotEver]

I have one of these:-

 

http://www.airlinktransformers.com/article/waterways-article.html

 

http://www.airlinktransformers.com/transformer/wp3231-weatherproof-transformer.asp

 

Martin

Note that the article linked in the first link refers to the Airlink 3230, but the better unit is the one linked in the second link - the 3231. The difference is that the 3231 has an interwinding screen which is connected to shore earth. I'm not even sure if the 3230 is still available.

 

Note also that if you take a look at the Victron IT it is often shown as having the boat's earth connected to the interwinding screen - this is wrong, as has been pointed out to them on more than one occasion. Not that this has any relevance to the Airlink job, but some folk might get confused when researching the subject. The Victron actually has a problem insofar as it has a metal case which needs therefore to be earthed... think about it.

 

Tony

[jonk]

Note that the article linked in the first link refers to the Airlink 3230, but the better unit is the one linked in the second link - the 3231. The difference is that the 3231 has an interwinding screen which is connected to shore earth. I'm not even sure if the 3230 is still available.

 

Note also that if you take a look at the Victron IT it is often shown as having the boat's earth connected to the interwinding screen - this is wrong, as has been pointed out to them on more than one occasion. Not that this has any relevance to the Airlink job, but some folk might get confused when researching the subject. The Victron actually has a problem insofar as it has a metal case which needs therefore to be earthed... think about it.

 

Tony

 

So if the Victron is onboard it would have to be isolated from the boat and an earth lead lead ashore (presumably in the 3 core wire)?

 

John

[DeanS]

Actually I need to confess and say I still dont understand

 

If my boat was parked up, and next to it, on the towpath there was a 220V supply...and I had an appliance, sitting on the towpath, plugged into the 220V, then at this point the boat is not affected by the 220V. Why then, if I simply life the appliance, and put it into the cratch area, do I suddenly need to get protection?

 

To me, this is all that happens when I connect to shore power...it's just a big extension lead, and all the 220V appliances connect to it, with no link to the boat at all.

 

so what am I missing?

[Tony Brooks]

Actually I need to confess and say I still dont understand

 

If my boat was parked up, and next to it, on the towpath there was a 220V supply...and I had an appliance, sitting on the towpath, plugged into the 220V, then at this point the boat is not affected by the 220V. Why then, if I simply life the appliance, and put it into the cratch area, do I suddenly need to get protection?

 

To me, this is all that happens when I connect to shore power...it's just a big extension lead, and all the 220V appliances connect to it, with no link to the boat at all.

 

so what am I missing?

 

Not a lot if it stays that way but trap cable in a door jamb, chaff a cable through or even just soak the back of a switch/plug and you could well make the hull of the boat live. This would have no immediate effect on you - until you stepped off the boat. Then you could get fried or a swimmer near the boat could get killed. However you would be putting the hull at risk form the moment it became live.

 

 

This is all about minimising potentially fatal risk

 

Water, contrary to popular belief, is not a particularly good conductor of electricity so it is possible for a line to hull fault not to trip a shoreside RCD or an MCB/fuse.

[DeanS]

Not a lot if it stays that way but trap cable in a door jamb, chaff a cable through or even just soak the back of a switch/plug and you could well make the hull of the boat live. This would have no immediate effect on you - until you stepped off the boat. Then you could get fried or a swimmer near the boat could get killed. However you would be putting the hull at risk form the moment it became live.

 

 

This is all about minimising potentially fatal risk

 

Water, contrary to popular belief, is not a particularly good conductor of electricity so it is possible for a line to hull fault not to trip a shoreside RCD or an MCB/fuse.

 

Are you saying that 220V earth on a boat is wired to the hull? Surely not?

I understand about minimising risk. Doesnt the 220V supply (on shore) have an earth leakage device? Surely standing on the boat is the same as standing on land with rubber shoes? In both cases, you (or you on the boat) are not a route to earth. I cant see how this has anything to do with corrosion of the boat, and I'm really hoping someone could clarify that.

[RLWP]

Are you saying that 220V earth on a boat is wired to the hull? Surely not?

I understand about minimising risk. Doesnt the 220V supply (on shore) have an earth leakage device? Surely standing on the boat is the same as standing on land with rubber shoes? In both cases, you (or you on the boat) are not a route to earth. I cant see how this has anything to do with corrosion of the boat, and I'm really hoping someone could clarify that.

 

Yes, you must wire the 240V earth to the boat hull. It's in one of the regulations, RCD or BSS or something

 

Richard

[DeanS]

Yes, you must wire the 240V earth to the boat hull. It's in one of the regulations, RCD or BSS or something

 

Richard

 

I see. Appliances use live and neutral and the earth is a safety wire, correct? Are you then saying that just by connecting the earth from 220V to the hull, this is the reason a GI is required, because there is an immediate charge of some sort. And if you say Yes, are you sure? ..because if you are sure, then it makes sense and a good argument to having a GI fitted...however...if the earth is just a "in case of an emergency" requirement, then..perhaps a GI isnt needed at all? (I have always believed the consensus that you have to have a GI, and I'll stick with that, but I wasn't sure why.)

[rjasmith]

I see. Appliances use live and neutral and the earth is a safety wire, correct? Are you then saying that just by connecting the earth from 220V to the hull, this is the reason a GI is required, because there is an immediate charge of some sort. And if you say Yes, are you sure? ..because if you are sure, then it makes sense and a good argument to having a GI fitted...however...if the earth is just a "in case of an emergency" requirement, then..perhaps a GI isnt needed at all? (I have always believed the consensus that you have to have a GI, and I'll stick with that, but I wasn't sure why.)

 

I think you might find the answers you're looking for on Gibbo's Smartgauge website here. This link will take you to the page on earthing and you might also want to delve further into the bits on other pages about GIs, ITs and other aspects of AC and DC supplies on boats.

 

Reading it will require a certain amount of ability to follow the technical discussion but if you're OK with that and have got the time it will make all of this stuff much clearer for you. It really is a very helpful site.

 

Richard

[churchward]

I see. Appliances use live and neutral and the earth is a safety wire, correct? Are you then saying that just by connecting the earth from 220V to the hull, this is the reason a GI is required, because there is an immediate charge of some sort. And if you say Yes, are you sure? ..because if you are sure, then it makes sense and a good argument to having a GI fitted...however...if the earth is just a "in case of an emergency" requirement, then..perhaps a GI isnt needed at all? (I have always believed the consensus that you have to have a GI, and I'll stick with that, but I wasn't sure why.)

I guess you could just not have an earth connection top the hull or to the land line and you will be protected from galavanic hull corrosion but you will NOT be protected from a wiring fault that makes the hull live with lovely mains power. You may just have time to regret the decision before you are fried to a crisp in the boat, stepping to the bank or drowned in the water.

[DeanS]

I guess you could just not have an earth connection top the hull or to the land line and you will be protected from galavanic hull corrosion but you will NOT be protected from a wiring fault that makes the hull live with lovely mains power. You may just have time to regret the decision before you are fried to a crisp in the boat, stepping to the bank or drowned in the water.

 

no no...I'm quite happy to go with the consensus

[bottle]

The simple answer, as I understand it, there may be an earth 'leakage' on your boat or another boat.

 

If your boat is at a different potential to the other boat then with the water you make a set up that they use in galvanising metal and depending on which way it is flowing then you will either gain metal (good) or lose metal (bad).

 

It will not be known which until it is possibly to late.

 

[smileypete]

Reading the discussions on bottom blacking and anodes I am coming to the conclusion that no-one REALLY KNOWS and has convincing proof, which is better/works best. So in light of that does anyone know, or have a convincing reason, whether a galvanic isolator will 100% protect a boat from corrosion caused by the attachment of a landline?

Thanks,

John

A properly installed galvanic isolator might only provide 99.9% protection which is good enough for some (most?) people.

 

However some want the 'peace of mind' from the 100% protection afforded by an isolation transformer.

 

If you put blacking on a boat some will fall/scrape off and there will be some corrosion, that is how it is.

 

cheers,

Pete.

[coreng]

Funny as simple things becomes complicated !

 

1) Yes, unprotected metal immersed in water rusts

2) Yes, rust always occur where a current goes out (and where isolating coating is gone)

3) Yes, 220 V must be grounded to metal hulls (otherwise it will go through you...). Search on Google ISO 13297 Small crafts alternating currents installations

4) Yes, earth wire brings in stray currents, who then goes into the hull and then out in the water... So, electrolytic corrosion occurs.

5) Yes, an isolation transformer stops stray currents from coming aboard through the earth wire

6) Yes, anodes are effective against galvanic corrosion

7) No, anodes are not effective against electrolytic corrosion and won't fight stray currents... or at least, not very long

8) Yes, everything can be (should be...) measured : efficiency of anodes and possible stray currents

9) Yes, all is necessary : coatings, anodes, isolation devices

 

We're in 2011 ! It's not black magic... And you're just missing knowledge.

 

Though...

[Keeping Up]

Funny as simple things becomes complicated !

 

1) Yes, unprotected metal immersed in water rusts

2) Yes, rust always occur where a current goes out (and where isolating coating is gone)

3) Yes, 220 V must be grounded to metal hulls (otherwise it will go through you...). Search on Google ISO 13297 Small crafts alternating currents installations

4) Yes, earth wire brings in stray currents, who then goes into the hull and then out in the water... So, electrolytic corrosion occurs.

5) Yes, an isolation transformer stops stray currents from coming aboard through the earth wire

6) Yes, anodes are effective against galvanic corrosion

7) No, anodes are not effective against electrolytic corrosion and won't fight stray currents... or at least, not very long

8) Yes, everything can be (should be...) measured : efficiency of anodes and possible stray currents

9) Yes, all is necessary : coatings, anodes, isolation devices

 

We're in 2011 ! It's not black magic... And you're just missing knowledge.

 

Though...

 

All correct but you forgot to mention Galvanic Isolators - which were after all the topic of this thread

[coreng]

All correct but you forgot to mention Galvanic Isolators - which were after all the topic of this thread

 

My apologies, isolators are included into protective devices...

 

10) No, galvanic isolators are not 100 % effective (and that is the question). Isolation transformer is better and much safer

Edited February 22, 2011 by coreng

[WotEver]

So if the Victron is onboard it would have to be isolated from the boat and an earth lead lead ashore (presumably in the 3 core wire)?

 

John

Yes