question

Hi

I'm in agreement with you that 36.4 ohms is too low for an open circuit and too high for a short or deliberate connection.

Question: the yellow/green wire coming out of your consumer unit - is that the PE for the consumer unit? If so why doesn't that come from the secondary of the IT?

What's in your shore power socket - is there a chance you have a "fortuitous earth" in there? Maybe something in contact with the ?metal? back plate?

Is there evidence of chafing where the shore power cable enters the boat?

Hello,

So the the green wire coming from the CU is attached to the busbar that the IT is connected to as well as my hull bond by the engine mounts. Both are attached to output side of the IT (IT Casing and CU).

Do you mean the earth on the shore or my Ceeform inlet on the boat? In the boat everything is in flexi or plastic components. If you mean the shore earth what should I bring looking for?

So in order for me to be getting this reading it’s either the IT isn’t working or my boat is somehow connected to shore earth somehow through the water or a faulty shore cable?

The purpose of the jumper between J5 and J7 is to bond the neutral to "earth" at the output of the IT (to ensure your RCDs operate) I don't see why you would also add a PE between your busbar and the CU since it should come from the IT? What happens to the reading with the busbar CU connection removed?

I would also look for damage to your shore power lead. Try substitution?

Yes I will try a substitute cable, Would this be caused by a break in the cable that’s travels through the water? Or a break in the cable onboard the boat somewhere making contact for the IT? That is essentially what I’m looking for isn’t it a connection for the IT.

I will also try a test with this CU earth.

Even with no alternate connections to shore earth what readings should I expect as I can only imagine is wouldn’t be an open connection because you are floating above the Shore ground essentially with the water as a barrier.

The purpose of the isolation transformer is to ensure that there is no physical path from the live/neutral and PE connections between the shore and the boat - so you should see an open circuit value.

Your reading indicates there is a parallel path from shore to the boat for at least the PE connection.

It's also possible there is a problem with the IT but I would check the wiring first.

The green/yellow wire that goes to one of the PCB mounting screws - is that something you added?

Your case connection to your busbar should use the M6 stud/nut between the 2 cable glands ....

I added the earth from the CU to the busbar I added and yes I used the M6 stud between the glands to ground the case within the boats earthing system.

The earth from the PCB I didn’t add it came this way and the manual doesn’t mention anything about it besides in the box your given a spare cable.

Could it be that one end in my boat is in the mud slightly? Grounding it that way?

I imagine your barge is blacked below the waterline ..... I don't think your issue is grounding of the hull by water or mud ..... my IT is open circuit except when the "spare" cable is connected when the boat is on dry land.

Would the shore cable being in the water for some of its journey to shore outlet be the potential issue? if it’s got a break in it?

Is that something you could take a picture of potentially? Your system I mean?

But in terms of protection right now with a reading like this, only in a fault scenario would I be experiencing any galvanic corrosion?

If the shore cable is faulty then mulitple things could be going on .... it would be better not in the water even if it's healthy.

My system looks similar to yours - incoming shore power lead to socket - socket to IT - IT to consumer unit - with appropriate breakers at each point. But sorry I can't dismantle the sofas to take pictures.

Galvanic corrosion is a complex subject but since the purpose of the IT is physical separation of shore and boat wiring I'd suggest you have a problem that needs fixing.

If you pull the shore power plug does the reading change between left-hand PE connection and your busbar?

I’m away from my boat at the moment but tomorrow I’ll conduct these tests.

Ok, so I’ve done some testing today. I think I have another issue.

With the shore power disconnected onboard my boat, testing between the Ceeform earth pin (Shore) and my onboard earthing point to the hull I get an ohms reading of 14.3 ohms. So my hull is in contact with the shore earth… And I get the same reading when connected through the transformer when it’s on. I tried this with 2 shore cables and one is completely out of the water.

What happening here if the boat earth is getting a resistance reading to shore earth without the shore lead even connected…

The earth from my ring circuit are completely open circuit from my hull earthing pointing as is the neutral and line. I believe that tells me it’s not faulty wiring?

There is something metallic connecting your hull to the pontoon.

Do you have a steel or aluminium passerelle/gangplank?

Not to my knowledge no. Could this be a connection through a neighbouring boat? Not sure what else it could be?

Hello, if you want to test the transformer and see if its working the procedure is... 1 take off all wiring and measure in L--> L-N output and N--> L/N output, this should be high in resistance. Then connect input L/N (and PE ) and measure enclosure/output PE against incoming PE. this should also be high in restistance. If not? check incoming cable for having the PE on the hull before reaching the transformer.

If high, then all is OK and the output can be connected.

From the last survey it had been double epoxy blacked and yes it’s in fresh water.

Notes from survey 2022

“The entire hull has been painted with epoxy primer. Above the waterline a two-pack topcoat has been applied. All found applied to a good professional standard with adequate dry film thickness”

So I did the tests that Johannes said and with everything disconnected in the output side I got a volts reading between the input PE and output PE.

-Shore connected

-IT on

-Output disconnected

-IT bond disconnected

-Neutral link in

When the I reconnect the IT bond to the hull I get no voltage reading but a low ohms reading again…

What does this mean?

Did you check if your engine is connected to your ship's ground? If so, you might have a ground path prop -> prop shaft -> engine -> ship's ground. If so, it wouldn't matter if your hull is perfectly isolated by its painting or not.

Actually that is the path where a good part of galvanic corrosion problems arise and exactly that is the reason for installing an isolation tranformer.

With an isolation transformer, the circuit

prop -> prop shaft -> engine -> ship's ground -> shore cable green wire -> shore -> water -> prop

is interrupted and everything is fine.

>>If this ground path through the prop is the case how do I make my transformer work as it should?

The ground path is not a problem by itself (provided you have properly equipped the prop and the hull with zinc anodes). The purpose of the transformer is to prevent DC currents from flowing, which it does perfectly.

Let's compare the system Boat-water-shore to a good old zinc battery. (Your boat is the negative cup, the water is the electrolytic paste and the shore is the positive graphite electrode).

As long as the battery lies in the cupboard, nothing happens. When someone attaches a wire to the plus and minus, current starts flowing and the zinc cup is slowly eaten up. That's why sometimes devices get wrecked by battery liquid when used batteries are not removed in time.

The same happens to your boat when you don't have an isolating device and connect the shore cable to your boat as well as the connection ashore. The electric circuit is closed, DC current starts flowing and damages your hull, your prop, your shaft.

That's where the isolating transformer comes in. With the isolation transformer, there is no galvanic connection between the shore and your boat. No DC current flows, your boat stays safe. Like the battery in the cupboard.