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


James Wendell <ms42phantom54@...>
 

Kent, I concur that we have probably beat this topic into the "ground," if you will, but I do want to at least respond to your questions if I can. Maybe I can help clarify, or at least emphasize why I think an unbonded neutral at the generator is a no-no under any circumstances. I will shut up after that and move on to other important issues as I ready my Amel for my journeys next year.

The neutral-to-ground (earth) connection creates a low-impedance path, which is necessary to clear a phase-to-ground fault for separately-derived system (in this case the Amel generator). This low-impedance path is created when the metal parts of the system (green/yellow equipment grounding conductor) is bonded to the system grounded conductor (blue neutral). This neutral-to-ground bond must be made at either:
(1)   the source of a separately-derived system (generator, transformer, or shore power source at the marina) or
(2)   the separately-derived system disconnecting means

DANGER: Failure to provide a low-impedance ground-fault path (that is, not connecting neutral to ground) for the generator can create a condition where a phase-to-ground fault cannot be removed. The result is that all metal parts of the electrical system, as well as the building structure will remain energized with dangerous line voltage if a phase-to-ground fault occurs.

You would not have to be standing in water for that to happen. Insulation could break down, wires could be cut, etc., and that could energize the generator frame. Touching it with your hand could be enough to electrocute.

By the way, the terms ground and earth are the same. The US tends to refer to it as ground, while those in Europe call it earth. I think "earth" is the term used in the Amel reference material I have.

Talk to you all later on other issues.

Thanks for the support.
Jamie
s/v Phantom Amel 54



On Saturday, December 5, 2015 9:12 AM, "Kent Robertson karkauai@... [amelyachtowners]" wrote:


 
AC

I understand, and agree that the risk of AC shock is very low, Alan.  I guess I could imagine a scenario where the boat was holed and needed continuous pumping of the bilge.  The generator might be needed especially if short-handed, you'd be wet, the boat would be wet, etc.

On the other hand, all European and ABYC standards call for grounding of the 220 system.  With a galvanic isolator the risk of damage from nearby boats or faulty shore power connections can be mitigated.

Oliver's post also says "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."  And his later post, "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." Implying that 220 Earth from shore power is connected to the bonding system already.  I thought that there were supposed to be NO connections between 220 and the bonding system.  Since all 220vAC appliances have their grounds (y/g wires) connected together in the 220 breaker panel, and at the ground lug in the ATS box, if there is a connection to the bonding system at the generator or any where else, then all 220 grounds are connected.  If the shore power is grounded to the bonding system, why would it be a problem to connect it again at the generator?

So please help me understand the down side of keeping this connection intact (ie having a connection between 220 ground and the corrosion bonding system via the generator output ground and engine connection to the bonding system).


DC
Now, regarding his last post about the 24vDC earth connections to the bonding system.  I guess I was getting "ground " and "earth" confused. When we say that Amel doesn't ground it's DC circuits to the bonding system, I think we are saying that the negative (-) wires are run directly back to the battery (-), rather than making that connection through the bonding system ("earth")...like we do when we isolate our engines by disconnecting 12vDC (-) from the engine block.  But the appliance cases are connected to earth (like our engine is connected to the bonding system), so that in the event of a (+) or (-)  fault in a pump, the current goes to the bonding system.  

What about any DC appliances like winches, windlass, bow thruster, fresh water pump, etc that are not under water, but are also susceptible to faults.  Are their cases also connected to the bonding system?  If not, where?

I was thinking that our DC systems were completely isolated from the corrosion bonding system, but I guess that at least the sea water pumps are connected anyway by the sea water.  I thought that if there was a short in a pump motor, it would follow a path back to the battery, rather than to the "earth" bonding system, protecting the bonded underwater metals from electrolysis.  Obviously I had that wrong.  Please explain again why Amel isolates the battery negative from earth.

Again, I apologize for whipping a horse that many of you know is already dead.  Every time I think I've got it, something comes up that throws me back into the dark ages.

I'm not going to give up Olivier.  I'm just hoping that one day I will understand it enough to stay out of trouble.  Thank you again for being so involved in this forum and taking your valuable time to help us understand our boats.  I wish I were a better student.

Kent
SM243
Kristy 





On Dec 5, 2015, at 4:16 AM, divanz620@... [amelyachtowners] <amelyachtowners@...> wrote:

 
I think you need to read Olivier;'s reply a bit more carefully :

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.


I would tend to agree with that...

Cheers
Alan
Elyse SM437


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