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galvanic isolator?


wetfoot

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I understand the reason for a GI when connected to shore power in a marina to prevent the small galvanic currents flowing from boat to boat.

But when moored at the side of the canal you have boat A connected via wet ropes to the metal mooring rail to which is also connected boat B by its wet ropes.

Isn't that the same situation as having a earth wire connecting the two boats, albeit with a bit more resistance ?

 

Should any special precautions be taken in that situation or is the resistance of the wet rope more than enough to stop damage?

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No precaution necessary, because the small voltage difference between the electric supply earth and the hull connection to earth via the water will not be enough to overcome the resistance of the ropes and thus drive a current.

 

One of my neighbours has jump leads clipped to his boat and the piling to ensure both are at exactly the same potential, but him not sure that works as well as a GI or ITx.

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I will be shortly moving my boat to a moorings with electric hook up at Fazeley Marina.

I will be using a maximum of 2kw.

Is the thingy below all I need to use and do.

 

https://www.ebay.co.uk/itm/Galvanic-Isolator-Boat-Plug-In-EXTRA-Protection-500-amp-LIFETIME-GUAR/291900024299?hash=item43f698e5eb:g:liQAAOSwDrpbp9DE:rk:5:pf:1&frcectupt=true

 

Sorry that I am absolutely no good at electrics.  

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14 minutes ago, cuthound said:

No precaution necessary, because the small voltage difference between the electric supply earth and the hull connection to earth via the water will not be enough to overcome the resistance of the ropes and thus drive a current.

 

One of my neighbours has jump leads clipped to his boat and the piling to ensure both are at exactly the same potential, but him not sure that works as well as a GI or ITx.

Ok, that's what I thought, otherwise we'd be seeing little ceramic insulators all along the canal.

Thanks

 

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5 hours ago, Laurie.Booth said:

Is the thingy below all I need to use and do.

It’s a GI. It will do what it says on the tin. It is definitely NOT “Gold Standard” as described; it appears to comply with no regulations and certainly not to the AYBC spec, which is indeed the gold standard. 

 

Whenever you trip anything - bollard, RCD on the shore, RCD on the boat etc - you must check the GI with a multimeter. It can fail open circuit (resulting in no earth connection at all) or short circuit (resulting in no protection), and there’s no way of knowing without checking it. 

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21 hours ago, cuthound said:

No precaution necessary, because the small voltage difference between the electric supply earth and the hull connection to earth via the water will not be enough to overcome the resistance of the ropes and thus drive a current.

 

One of my neighbours has jump leads clipped to his boat and the piling to ensure both are at exactly the same potential, but him not sure that works as well as a GI or ITx.

 

Surely that's doing the opposite of what a GI or IT does? Your neighbour is deliberately connecting his boat to earth rather than isolating it. Hasn't he created a circuit which may generate galvanic currents between the submerged dissimilar metals?

 

As you say, if you have no shore power connected then no isolation is required. So assuming you don't have shore power at your moorings it seems like your neighbour has the worst of both worlds - no shore power and potentially galvanic corrosion! On the other had if you do have shore power then he's bypassed his GI or IT (assuming he has one) with the jump leads. If the boat is on shore power without earth isolation then perhaps he's just created additional galvanic circuit paths with the jump leads?

 

What is it they say about a little bit of knowledge...   ?

corrosion2.jpg

Edited by blackrose
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59 minutes ago, blackrose said:

 

Surely that's doing the opposite of what a GI or IT does? Your neighbour is deliberately connecting his boat to earth rather than isolating it. Hasn't he created a circuit which may generate galvanic currents between the submerged dissimilar metals?

 

As you say, if you have no shore power connected then no isolation is required. So assuming you don't have shore power at your moorings it seems like your neighbour has the worst of both worlds - no shore power and potentially galvanic corrosion! On the other had if you do have shore power then he's bypassed his GI or IT (assuming he has one) with the jump leads. If the boat is on shore power without earth isolation then perhaps he's just created additional galvanic circuit paths with the jump leads?

 

What is it they say about a little bit of knowledge...   ?

corrosion2.jpg

 

Indeed, but his view is that if all earths are connected together, there is no voltage to drive a current, even though the boat is permanently plugged into the mains when not cruising.

 

According to him he has done this for over 10 years and claims no hull  corrosion.

 

Me, I use a GI and test it periodically to ensure it gives effective isolation whilst my boat is connected to mains between cruises.

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18 hours ago, WotEver said:

It’s a GI. It will do what it says on the tin. It is definitely NOT “Gold Standard” as described; it appears to comply with no regulations and certainly not to the AYBC spec, which is indeed the gold standard. 

 

Whenever you trip anything - bollard, RCD on the shore, RCD on the boat etc - you must check the GI with a multimeter. It can fail open circuit (resulting in no earth connection at all) or short circuit (resulting in no protection), and there’s no way of knowing without checking it. 

Thanks for the information is there a GI that you think I should buy? Or how do I check a GI with a multimeter?

Cheers 

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2 hours ago, cuthound said:

 

Indeed, but his view is that if all earths are connected together, there is no voltage to drive a current, even though the boat is permanently plugged into the mains when not cruising.

 

According to him he has done this for over 10 years and claims no hull  corrosion.

 

Well he's spectacularly wrong! He's connected his boat to earth without any form of isolation and in doing so he's actually created a potential difference between his boat and any connected and submerged dissimilar metals. If his boat hasn't suffered from any galvanic corrosion then I think that's just down to luck and blacking rather than anything else. 

 

My view (and I may be wrong) is that shore power earth isolation is more of a "last line of defence" for anything that might be going on rather than your first line of defence (paint). There are probably plenty of boats plugged into shore power on fresh water moorings all over the world without any form of earth isolation which haven't suffered from galvanic corrosion, but then there are others that do. There are lots of variables including water quality (electrolyte), the proximity and nobility of other metals in the water, etc. Anyway, the bottom line is that your neighbour has got the theory all wrong and has just been lucky.

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8 hours ago, Laurie.Booth said:

Sadly I didn't understand the video. So I assume the GI I was looking at is not suitable for me.

Put simply...

 

1. Ensure that you have a multimeter that includes a diode test function (most do these days). 

 

2. Disconnect the plug-in GI from the mains at both ends. 

 

3. Connect the two ends of the GI together - plug it into itself. 

 

4. Unplug the GI from itself. 

 

5. Using the multimeter on the diode test range read between the earth pins of the GI from the plug on one end to the socket on the other end. You should see the reading start at 0 and then slowly rise to about 0.9. 

 

6. Repeat steps 3 & 4. 

 

7. Repeat step 5 but connect the multimeter the other way around, (so if you had the black lead on the plug end the first time then this time it should be on the socket end). 

 

If steps 5 & 7 both perform as described then the GI is good. If they don’t then it isn’t. 

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5 hours ago, WotEver said:

Put simply...

 

1. Ensure that you have a multimeter that includes a diode test function (most do these days). 

 

2. Disconnect the plug-in GI from the mains at both ends. 

 

3. Connect the two ends of the GI together - plug it into itself. 

 

4. Unplug the GI from itself. 

 

5. Using the multimeter on the diode test range read between the earth pins of the GI from the plug on one end to the socket on the other end. You should see the reading start at 0 and then slowly rise to about 0.9. 

 

6. Repeat steps 3 & 4. 

 

7. Repeat step 5 but connect the multimeter the other way around, (so if you had the black lead on the plug end the first time then this time it should be on the socket end). 

 

If steps 5 & 7 both perform as described then the GI is good. If they don’t then it isn’t. 

Is there a GI made that I don't have to do this?

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21 minutes ago, Laurie.Booth said:

Is there a GI made that I don't have to do this?

Yes.

 

Any that comply with the AYBC spec, but they're a lot more expensive. Sterling make one that complies with that spec. 

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23 hours ago, blackrose said:

 

My view (and I may be wrong) is that shore power earth isolation is more of a "last line of defence" for anything that might be going on rather than your first line of defence (paint). There are probably plenty of boats plugged into shore power on fresh water moorings all over the world without any form of earth isolation which haven't suffered from galvanic corrosion, but then there are others that do. There are lots of variables including water quality (electrolyte), the proximity and nobility of other metals in the water, etc. Anyway, the bottom line is that your neighbour has got the theory all wrong and has just been lucky.

 

I'm no chemist but I suspect that the presence or absence of galvanic corrosion depends mostly on what is (or is not) dissolved in the local canal water.

 

I agree wholeheartedly about the blacking being the first line of defence though.

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3 hours ago, Laurie.Booth said:

Is there a GI made that I don't have to do this?

Yes those with a status indicator. 

 

You just need a 9v (pp3) battery to test its ok periodically or after an overload trip. Safeshore include a pp3 connector and instructions in there indicator versions. (Other makes available) 

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6 hours ago, jonathanA said:

Yes those with a status indicator. 

 

You just need a 9v (pp3) battery to test its ok periodically or after an overload trip. Safeshore include a pp3 connector and instructions in there indicator versions. (Other makes available) 

Have you got a link?

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16 minutes ago, canalboat said:

I have a mains lead going from shore to a small oil-filled radiator in the boat to protect against freezing but it is not earthed to the boat. Does that need a GI?

 Unless the  radiator is double insulated then any metal casing will be connected to the "earth" cable. If the radiator case made contact with ANY conductive material (could be wet flooring) that makes contact with the hull then it is possible to get corrosion. However as an unqualified opinion I would say that is not very likely but might happen if it fell against or touched any metal heating components or domestic appliances.

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