Fitting a galvanic isolator

[robtheplod]

Thanks for the replies.... so.. I'm thinking getting as Nick has above as it seems to imply ABYC compliance and has an indicator on it:

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

purchased from https://www.mecmarine.co.uk/shop/galvanic-current-isolator-16a-with-indicator/

For the money (or thereabouts) is this as good as I can get in GI terms??

[blackrose]

46 minutes ago, robtheplod said:

Thanks for the replies.... so.. I'm thinking getting as Nick has above as it seems to imply ABYC compliance and has an indicator on it:

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

purchased from https://www.mecmarine.co.uk/shop/galvanic-current-isolator-16a-with-indicator/

 

 

For the money (or thereabouts) is this as good as I can get in GI terms??

 

My 14 year old 70 amp GI blocks currents below 2.4v. 

 

1.1 volts seems a bit on the low side so could the diodes be forced into conduction by RFI currents from switch-mode mains appliances? That will be fine but only if you happen to notice the indicator. If the GI isn't located inside the cabin that might be difficult. For most installations I think you're better off with a remote indicator GI

 

What actually makes that Aquafax GI ABYC compliant? Is it the additional capacitor?

Edited May 6, 2020 by blackrose

[robtheplod]

21 minutes ago, blackrose said:

 

My 14 year old 70 amp GI blocks currents below 2.4v. 

 

1.1 volts seems a bit on the low side so could the diodes be forced into conduction by RFI currents from switch-mode mains appliances? That will be fine but only if you happen to notice the indicator. If the GI isn't located inside the cabin that might be difficult. For most installations I think you're better off with a remote indicator GI

 

What actually makes that Aquafax GI ABYC compliant? Is it the additional capacitor?

I was afraid some query would come back...… will I ever find the 'perfect' GI?

[Keeping Up]

6 minutes ago, robtheplod said:

I was afraid some query would come back...… will I ever find the 'perfect' GI?

Have you got the GI Blues?

 

 

[blackrose]

6 minutes ago, robtheplod said:

I was afraid some query would come back...… will I ever find the 'perfect' GI?

No. The perfect GI is an IT, but even they are not perfect.

 

Before you buy a lower spec but ABYC compliant GI, have a look at the higher spec but non-ABYC compliant Safeshore units. I'm not saying they are better but they can definitely handle a higher voltage before going into conduction.

 

https://www.safeshoremarine.com/

 

 

 

[nicknorman]

24 minutes ago, blackrose said:

 

My 14 year old 70 amp GI blocks currents below 2.4v. 

 

1.1 volts seems a bit on the low side so could the diodes be forced into conduction by RFI currents from switch-mode mains appliances? That will be fine but only if you happen to notice the indicator. If the GI isn't located inside the cabin that might be difficult. For most installations I think you're better off with a remote indicator GI

 

What actually makes that Aquafax GI ABYC compliant?

There was talk about switch mode supplies “leaking” transient currents to earth, but this is mostly one of those urban myth things that might have had a grain of truth at one point, but no longer does. Phone chargers were cited. But if you look at virtually any phone charger these days it doesn’t even have an earth connection (plastic earth pin) so it can’t possibly dump transients to earth, and it has long been against EU rules to dump current into the earth connection. So a red herring.

 

As to the number of diodes, all I can say is that we have plugged into a good few shore connections but I have never seen the meter move more than about 1/4 way up the green band.

[blackrose]

4 minutes ago, nicknorman said:

There was talk about switch mode supplies “leaking” transient currents to earth, but this is mostly one of those urban myth things that might have had a grain of truth at one point, but no longer does. Phone chargers were cited. But if you look at virtually any phone charger these days it doesn’t even have an earth connection (plastic earth pin) so it can’t possibly dump transients to earth, and it has long been against EU rules to dump current into the earth connection. So a red herring.

 

As to the number of diodes, all I can say is that we have plugged into a good few shore connections but I have never seen the meter move more than about 1/4 way up the green band.

 

Is your GI mounted so that you can see the indicator most of the time? If so then I'd say that's fine. If not then I question the point of a built in (rather than remote) indicator. If the GI is down in the engine hole for example, how often is it actually going to be viewed?

Edited May 6, 2020 by blackrose

[robtheplod]

My next question would be how often do people look at the GI?  are there events whereby your next step is to take a look or is it something you keep an eye on as you walk past?

[cuthound]

Just now, robtheplod said:

My next question would be how often do people look at the GI?  are there events whereby your next step is to take a look or is it something you keep an eye on as you walk past?

 

I have a Victron GI without any fault indication fitted.

 

I check it using the diode scale on a digital multimeter roughly every 3 months, and have for the past 6 years. Obviously it is only working when connected to the shoreline, so no need to check when our cruising, unless you connect to.a shoreline.

 

So far no problems.

 

I would also check it if the RCD ever trips.

 

 

[nicknorman]

This statement in the safe shore brochure makes me realise that safe shore don’t have a clue what they are talking about:

 

“15 amps, 30amps, 70 amps, 100 amps? What does it mean? A question we are asked all the time. Basically the amperage rating of the isolator is the amount of current the isolator can handle under severe fault conditions. The isolator must be able to handle more than the available current supplied to the boat. Usually UK marina supplies are either 16 or 32 amps so the isolator must be able safely handle at least 20% more than the maximum current available to comply with legislation. Realistically the higher the rating the more reliable the isolator”

 

If they imagine that a 16A shore connection socket can only supply 16 x 1.2 = 19.2A under “severe fault conditions” they are barking. More like a few 1000A.

 

They are confusing the “legislation” for over-rating current carrying capability of power conductors, with a possible maximum short term fault current, which is a totally different thing. No wonder the ABYC standard doesn’t get a mention! They may protect up to 2 volts or whatever, but I bet at the first sign of a short circuit to earth they will disappear in a puff of smoke.

[cuthound]

2 minutes ago, nicknorman said:

This statement in the safe shore brochure makes me realise that safe shore don’t have a clue what they are talking about:

 

“15 amps, 30amps, 70 amps, 100 amps? What does it mean? A question we are asked all the time. Basically the amperage rating of the isolator is the amount of current the isolator can handle under severe fault conditions. The isolator must be able to handle more than the available current supplied to the boat. Usually UK marina supplies are either 16 or 32 amps so the isolator must be able safely handle at least 20% more than the maximum current available to comply with legislation. Realistically the higher the rating the more reliable the isolator”

 

If they imagine that a 16A shore connection socket can only supply 16 x 1.2 = 19.2A under “severe fault conditions” they are barking. More like a few 1000A.

 

They are confusing the “legislation” for over-rating current carrying capability of power conductors, with a possible maximum short term fault current, which is a totally different thing. No wonder the ABYC standard doesn’t get a mention! They may protect up to 2 volts or whatever, but I bet at the first sign of a short circuit to earth they will disappear in a puff of smoke.

 

Several GI manufacturers make the same mistake.

 

It seems many manufacturers of GI's and IT's have no ideas how to calculate prospective fault current. 

Edited May 6, 2020 by cuthound
To unmangle the effects of autocorrect.

[robtheplod]

....... so its no wonder I'm absolutely confused when it comes to getting something I can rely on to protect the boat.... I do worry about this as its a significant problem as I'm on shoreline 95% of the time and I'd only know if a device wasn't really up to it/working when the resultant problem becomes evident and its then all too late...... and you can bet your bottom dollar there is no comeback with any of these devices?

[nicknorman]

6 minutes ago, robtheplod said:

My next question would be how often do people look at the GI?  are there events whereby your next step is to take a look or is it something you keep an eye on as you walk past?

Ours is in a cupboard so not immediately obvious. I look at it whenever we plug into a new shore supply. There is quite a variation of indications.

 

As said you should check it after any breaker-tripping event and really, this needs to be done by testing with a digital meter on diode test mode (or battery + bulb + voltmeter). The built in meter won’t indicate if the diodes are open circuit, and the meter will indicate zero both if the diodes are short circuit or if there just isn’t any voltage offset on the shore earth.

[ditchcrawler]

Earth fault currents is a whole different ball game to what the  supply current is.  Those diodes are in your earth line and if they fall to bits before your breaker trips then you have no earth protection.

[nicknorman]

4 minutes ago, robtheplod said:

....... so its no wonder I'm absolutely confused when it comes to getting something I can rely on to protect the boat.... I do worry about this as its a significant problem as I'm on shoreline 95% of the time and I'd only know if a device wasn't really up to it/working when the resultant problem becomes evident and its then all too late...... and you can bet your bottom dollar there is no comeback with any of these devices?

My advice remains to get a GI that meets the ABYC standard. Our boat has been plugged into shore power with the Aquafax GI for the last 10 years except when we are out, so far the boat hasn’t turned into a tea strainer.

[Flyboy]

48 minutes ago, nicknorman said:

My advice remains to get a GI that meets the ABYC standard. Our boat has been plugged into shore power with the Aquafax GI for the last 10 years except when we are out, so far the boat hasn’t turned into a tea strainer.

I also have an Aquafax 16 Amp GI fitted since 2009.  I did a little test to see how sensitive it was by connecting a small mains neon between  L & E. The result was that the meter needle deflected about 2mm but well within the green sector. I concluded that as the neon was very low current it gave a good indication of earth leakage. I've never seen the needle off the zero in normal useage.

[nicknorman]

4 hours ago, Flyboy said:

I also have an Aquafax 16 Amp GI fitted since 2009.  I did a little test to see how sensitive it was by connecting a small mains neon between  L & E. The result was that the meter needle deflected about 2mm but well within the green sector. I concluded that as the neon was very low current it gave a good indication of earth leakage. I've never seen the needle off the zero in normal useage.

Don’t forget that galvanic corrosion is caused by dc current caused by a dc voltage offset between the shore earth wire, and local earth. By introducing the neon, you introduced mostly ac current, which the meter wouldn’t register. I guess it moved a bit due to some slight rectification effect of the neon.

[blackrose]

12 hours ago, nicknorman said:

My advice remains to get a GI that meets the ABYC standard. Our boat has been plugged into shore power with the Aquafax GI for the last 10 years except when we are out, so far the boat hasn’t turned into a tea strainer.

 

Likewise my boat has been plugged into shore power for the last 15 years with a Safeshore GI and it's still working fine and my boat isn't suffering from any galvanic corrosion. I test it from time to time but I'm not knowledgeable enough to know what the difference is between mine and an ABYC complaint model. I did ask the question but nobody else seems to know either (at least I didn't see an answer to my earlier question).

[nicknorman]

56 minutes ago, blackrose said:

 

Likewise my boat has been plugged into shore power for the last 15 years with a Safeshore GI and it's still working fine and my boat isn't suffering from any galvanic corrosion. I test it from time to time but I'm not knowledgeable enough to know what the difference is between mine and an ABYC complaint model. I did ask the question but nobody else seems to know either (at least I didn't see an answer to my earlier question).

It’s to do with what happens if you have a short circuit from live to earth on your boat.

 

If that doesn’t happen, your non-ABYC compliant GI will do just the same job as a ABYC-compliant one.

 

If it does happen, your 16A supply can in fact deliver perhaps 1000A instantaneous current. Of course after a few 10s of milliseconds of that, one would expect the breaker on the bollard to trip. But 1000A going through the diode, even for a very short period of time (10mS), may melt the diode (the actual semiconductor junction is very small and thus has very small thermal mass). If the diode fails open circuit, it means your boat is no longer earthed, but you don’t realise it. I guess it might even be possible for the diode to melt and go open circuit before the breaker trips and the breaker then decides it doesn’t need to trip, so the hull becomes live.

 

Anyway the point being that an ABYC compliant GI can survive a pretty high fault current and if it does fail, it is guaranteed to fail short circuit so the boat remains earthed.

 

I’m sure you are thinking “Yeabut I’m not going to have a short circuit between live and earth” and you are probably right. Probably, but not definitely.

 

I suppose the bottom line is that there’s not much point in earthing your hull if the first time there’s a fault, the earth connection no longer exists. Even though that fault is fairly unlikely.

 

 

Edited May 6, 2020 by nicknorman

[robtheplod]

Just for info I've gone with this:

https://www.ebay.co.uk/itm/Marine-Galvanic-Current-Isolator-16A-with-Indicator-Ideal-for-all-boats-yachts/312013489840?epid=11010557562&hash=item48a57406b0:g:e~sAAOSwhVxaHoZp

much better price on ebay to the supplier I had intended...

 

rob

[ditchcrawler]

2 hours ago, robtheplod said:

Just for info I've gone with this:

https://www.ebay.co.uk/itm/Marine-Galvanic-Current-Isolator-16A-with-Indicator-Ideal-for-all-boats-yachts/312013489840?epid=11010557562&hash=item48a57406b0:g:e~sAAOSwhVxaHoZp

much better price on ebay to the supplier I had intended...

 

rob

Did you buy the last one?

[robtheplod]

7 minutes ago, ditchcrawler said:

Did you buy the last one?

looks like it...

[ditchcrawler]

On 06/05/2020 at 10:11, nicknorman said:

 

 

As said you should check it after any breaker-tripping event and really, this needs to be done by testing with a digital meter on diode test mode (or battery + bulb + voltmeter).  

I bet there are a lot of boaters who never do that and probably don't even know what the GI is

[robtheplod]

Just now, ditchcrawler said:

I bet there are a lot of boaters who never do that and probably don't even know what the GI is

As soon as I became aware of this (before getting the boat) it was my number one worry/thing to sort - didn't want it to dissolve!  Replacing my inline plugin one with this one when it arrives and i can get to the boat.....

[nicknorman]

47 minutes ago, ditchcrawler said:

I bet there are a lot of boaters who never do that and probably don't even know what the GI is

True. Including me, up to about 10 years ago. Before that we used to borrow my mate's various boats (or hire). He didn't believe in new fangled things like ac systems on boats. His last (and current) narrowboat had a shore connector that was only ever plugged in for 30 mins to hoover the boat out when we returned it to the marina. It definitely didn't have or need a GI. But once you look at getting your own boat with fancy electrics, you have to learn!

Edited May 7, 2020 by nicknorman