Generator and GI/IT

[jonathanA]

I was just looking at a friends Boat/mooring set up over the BH weekend and he has a  generator nicely installed ashore (private mooring, no Mains electricity),  I noticed a proper earth rod and everything.  

 

However I don't recall seeing a GI or IT at the time, but thinking about it, as there is no other boat connected to his generator and no other electrical connections to other boats, then my thinking is, that there is no need for a galvanic isolator or isolation tranny as there would not be any of those nasty stray currents causing corrosion or am I missing something  ?

[Alan de Enfield]

As far as I remebber it is only a problem if more than one boat is on an earth (like 3 or 4 boats all using a common earth on a bollard)

 

So, I'd say you are correct he doesn't need a GI or IT

 

 

 

[nicknorman]

36 minutes ago, jonathanA said:

I was just looking at a friends Boat/mooring set up over the BH weekend and he has a  generator nicely installed ashore (private mooring, no Mains electricity),  I noticed a proper earth rod and everything.  

 

However I don't recall seeing a GI or IT at the time, but thinking about it, as there is no other boat connected to his generator and no other electrical connections to other boats, then my thinking is, that there is no need for a galvanic isolator or isolation tranny as there would not be any of those nasty stray currents causing corrosion or am I missing something  ?

I think the need for a GI/IT is mostly because the earth pin on the shore bollard may be at a different voltage from the local earth. So if there is no shore bollard, only a very local earth, there is no need for a GI/IT

[jonathanA]

Thanks Nick. I also think the earth conductor can provide a path to/from other boats, which won't happen in this instance either. 

[DShK]

Are you sure the earthing rod actually works? I believe it can be pretty hard to get a proper earth with such a thing.

[nicknorman]

23 minutes ago, DShK said:

Are you sure the earthing rod actually works? I believe it can be pretty hard to get a proper earth with such a thing.

 

But then again, is it actually necessary? I wouldn't worry about it too much.

[Alan de Enfield]

25 minutes ago, DShK said:

Are you sure the earthing rod actually works? I believe it can be pretty hard to get a proper earth with such a thing.

 

Our 15,000v electric fencing requires an earth rod. I have a 3' long 12mm diameter steel spike which I knock (full length) into the ground, normally we get a pefect earth, but occasionally if the ground is very dry I need to pour a bucket of water all around the spike to get a good earth.

[jonathanA]

7 minutes ago, DShK said:

Are you sure the earthing rod actually works? I believe it can be pretty hard to get a proper earth with such a thing.

I heard the same, but the ground was fairly wet nearby and it looked like a decent rod. 

5 hours ago, Alan de Enfield said:

As far as I remebber it is only a problem if more than one boat is on an earth (like 3 or 4 boats all using a common earth on a bollard)

 

So, I'd say you are correct he doesn't need a GI or IT

 

 

 

Thanks Alan that was the picture I had in my head, but wasn't sure if there were any other factors. I seem to recall people talking about being up against metal pilings being  an issue. ( wouldn't be in the case of my friends mooring)

[blackrose]

15 hours ago, jonathanA said:

Thanks Nick. I also think the earth conductor can provide a path to/from other boats, which won't happen in this instance either. 

 

Surely it would happen, via the earth rod to any submerged metal also connected to earth in the vicinity? It doesn't need to be a boat.

[jonathanA]

13 minutes ago, blackrose said:

 

Surely it would happen, via the earth rod to any submerged metal also connected to earth in the vicinity? It doesn't need to be a boat.

No I dont think so as that metal would be at the same potential as the earth rod, and in any case unless it was somehow connected to the boat hull then I don't see how there would be any galvanic currents so not a problem.  (from a Boat point of view)

 

could be interesting if the boat was chained to steel pilings for example, possibly giving a direct metal path from hull to earth. (bypassing any GI/IT ?)

 

I'm not 100% sure which was why I asked here ! 

Edited August 30, 2023 by jonathanA
clarity

[pearley]

14 hours ago, Alan de Enfield said:

 

Our 15,000v electric fencing requires an earth rod. I have a 3' long 12mm diameter steel spike which I knock (full length) into the ground, normally we get a pefect earth, but occasionally if the ground is very dry I need to pour a bucket of water all around the spike to get a good earth.

In our first house we had a party line telephone which relied on an earth rod. We too had to pour water over it in dry weather to make a call. It wasn't until a few years later when our power failed that we found the rod had damaged to underground mains cable into the house.

[Sea Dog]

15 hours ago, DShK said:

Are you sure the earthing rod actually works? I believe it can be pretty hard to get a proper earth with such a thing.

Yes, because if you aren't getting a proper earth on such a thing thing, you fail the mandatory testing until you do. 

[blackrose]

On 30/08/2023 at 09:29, jonathanA said:

No I dont think so as that metal would be at the same potential as the earth rod, and in any case unless it was somehow connected to the boat hull then I don't see how there would be any galvanic currents so not a problem.  (from a Boat point of view)

 

 

No I don't think you understand how a large galvanic circuit works.

 

The submerged metal piling on the bank may be at the same potential at the earth rod but may not be at the same potential as the boat! 

 

And it's somehow connected to the boat via earth/earth rod and via weak galvanic currents in the water. That's the whole point!

 

Here's that image again... Everything connected to earth including any submerged metal such as steel pilings can form a galvanic circuit with a boat that's connected with an earth cable. It doesn't have to be another boat.

Edited August 31, 2023 by blackrose

[jonathanA]

1 hour ago, blackrose said:

 

No I don't think you understand how a large galvanic circuit works.

 

The submerged metal piling on the bank may be at the same potential at the earth rod but may not be at the same potential as the boat! 

 

And it's somehow connected to the boat via earth/earth rod and via weak galvanic currents in the water. That's the whole point!

 

Here's that image again... Everything connected to earth including any submerged metal such as steel pilings can form a galvanic circuit with a boat that's connected with an earth cable. It doesn't have to be another boat.

I think I do, but maybe you could have made yourself more clear  🙂 and  i misunderstood.  I agree any pilings jetties or whatever that is connected to mains (or generator in this case) earth could form part of a galvanic circuit, if thats the right term.  in the case I'm referring to there is no 'AC green wire' in your diagram above connecting the boat to the generator to sunken steel piling or or whatever, (only earth from the gennie to boat)  so no problem.   

what I said was :

 

"No I dont think so as that metal would be at the same potential as the earth rod, and in any case unless it was somehow connected to the boat hull then I don't see how there would be any galvanic currents so not a problem."

 

this is the case isn't it ? the diagram is showing a different scenario where there IS a connection to the boat /piling and therefore I agree a risk of galvanic action. 

 

I go on to say :

"could be interesting if the boat was chained to steel pilings for example, possibly giving a direct metal path from hull to earth. (bypassing any GI/IT ?)"

 

which is then the same (or similar) to the diagram and actually a bit worse as you could be smugly thinking your GI/IT is doing its job and I think (happy to be corrected) it isn't. although I think its likely to be far harder for a galvanic circuit to be made in those sorts of situations compared to say boats in close proximity sharing the same electrical Earthing system and same pilings/jetty metal work with no GI/IT involved. 

 

so I think we are actually in agreement and as I've said I started this thread because I wanted to learn/understand more and its really useful to debate and explore the different possibilities so thanks for that.