Re: [Amel Yacht Owners] Re: Prop Shaft Electrolysis

Beaute Olivier

Hi Kent,

the 24V pumps cases must be connected to the ground. There is only one ground aboard (also called equipotential circuit): all the yellow/green wires, where the zincs are connected, where every piece of metal in touch with seawater should be connected and where the 220V earth is connected when you're plugged to shore power.
Don't connect the 24V negative (or the 12V negative) to any equipment's casing/box.
The galvanic isolator will prevent ONLY the stray currents coming through the shore power cord to affect your vessel.

Sometimes, an equipment with a motor (with carbon brushes) creates a leak because the carbon dust (from woen carbon brushes) is making a connection between the 24V positive (of the motor) and the ground (motor's casing) or between the 24V negative (of the motor) and the ground. This is when you could have a damage from electrolytic corrosion (corrosion created by power). Galvanic corrosion is not created by a source of power but by the difference of potential between different metals  that touch each other and are in a conductive solution (seawater).
A quick corrosion of any metal (even your zincs) is most probably caused by a power leakage. A slow corrosion is, most of the time, the result of galvanic corrosion.

Don't give up!!!


On Friday, December 4, 2015 10:27 PM, "Kent Robertson karkauai@... [amelyachtowners]" wrote:

That seems like it leaves Amel folks at risk of 220 AC shock.  I just spoke to an engineer at Newmar (they make my galvanic isolator).  He said if your AC~ ground is not connected to the corrosion bonding system, the galvanic isolator is doing nothing!

If as on my boat, the 220 ground 
wire on the generator output is connected to the generator housing, then the galvanic isolator is working and I should be protected on the boat from electrical faults and from stray shore power current.

What is the down side of connecting the 220 ground to the corrosion bonding system?

As an aside, I have discovered that the head macerator pumps and the anchor wash pump are grounded to my corrosion bonding system.  That's DC connection and could cause electrolysis.  Am I correct in saying that the cases should be connected to battery negative instead?  That's going to be a royal PITA to run wires from one end of the boat to the other.  Has anyone done that?

It seems that the previous owner converted much of my electrical system to ABYC standards.


On Dec 4, 2015, at 2:46 PM, divanz620@... [amelyachtowners] <amelyachtowners@...> wrote:

This is Olivier's previous post on this subject :

Hello everybody,

I'm wondering why some SMs have passed the EWOF and some haven't...
However, the generator neutral has never been connected to the ground on SMs and AMEL 54.

When the generator is running and feeding the vessel, the only way for the ground fault breaker to trip in case of a leak Live wire touching the body of a 230V equipment) is to have the neutral connected to the ground circuit (yellow/green wires network).
If some of you decide to have the generator neutral connected to the ground, they must make sure that they do it at the generator output, and, for instance, not at the main breaker in galley, or at the automatic solenoid switch output (in engine room). Someone in this thread wrote that it is mentioned in the ONAN manual.

It is not clear why AMEL decided not to connect the neutral and the ground on these vessels.
They are now doing it on the AMEL 55 and 64.
The rule ISO 13297 concerning 230V AC installations in leisure vessels states that the neutral from an inside generator (diesel generator or 24V/230V inverter) should be connected to the vessel's ground equipotential circuit. I guess the recommendations from ABYC are the same about that.

To be electrocuted while the generator is running, and on a vessel where the generator neutral is not connected with the ground, you would need to be wet, with wet feet touching a conductive part of the vessel that would also be in touch with the neutral of the generator AND there should be a Live wire touching the metal body of a 230V appliance. That can however happen when the vessel is flooded with seawater and you run the generator.
The risk of being electrocuted on an AMEL vessel is probably small, because the bottom of the boat is (should be) rather dry.
You can also routinely check (or have checked) the isolation of the 230V appliances (is there a connection between the Live of the appliance's cable and the metal body of the appliance? The answer should be: resistance infinite).

For those who are not familiar with electricity, I simply say that the risk is much bigger on land where the place where you put your feet is sometimes very conductive (wet feet on concrete or tiled floor).

I'm sure that the above will raise hundreds of questions, so, feel free to ask...

Have a good day and don't flood your AMEL...


Join to automatically receive all group messages.