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

James Wendell <ms42phantom54@...>

Kent, again thanks for the kind words about my engine failure on Phantom. Just to confirm my comments, I am not suggesting the exhaust design was necessarily at fault, but in my case the layout of the system certainly could have exacerbated my engine failure. In any event, if I can take steps to improve with my new engine, I will.

If I can comment on your AC findings, I understand that Amel deliberately does not connect the AC earth to the DC bonding grid. That, of course, is totally opposite from US regulations that mandate that connection for safety, a practice to which I fully subscribe as an electrical engineer. There is also the absolute "no-no" of connecting AC neutral to earth anywhere on the boat unless you have an isolation transformer.

The exception, however, is at a separately-derived power source. For a shore power connection, the neutral-to-earth bond would be at the shore power source in the marina. For a generator, it would be at the generator. When the automatic transfer switch (ATS) is in shore power mode, it ensures the neutral is connected only to the shore power feeder and not the boat. It also ensures the grounding systems are not interconnected, since the neutral is not connected to the boat systems. Further the generator case will be connected to earth, since the battery negative for the starter lands on the frame. When the ATS is switched to generator, the neutral "should" be tied to AC earth, since it "should" be bonded to PE at the generator. You should verify the connection between the blue neutral wire and the green/yellow PE. If it is connected you are safe; if not, and you had a fault in an AC circuit to earth, the neutral would not have a return path to its source and the AC current would try to find an alternate path - not good.

Many don't I know, but technically an inverter is a separately-derived power source, and the neutral there should be tied to earth as well. The problem is that most inverters also function in pass-through mode.

I hope that helps. Let me know what you find.

s/v Phantom Amel 54

On Thursday, December 3, 2015 7:42 AM, "karkauai@... [amelyachtowners]" wrote:

Well, I have separated all the 220AC ground wires at the 220 box in the galley and at the 220 boxes in the engine room. I found that the output cable from the generator is grounded to the generator case, and thus, to the bonding system. The other end of that cable goes to the automatic switch that chooses generator over shore power, where it is connected to all other 220 grounds via the output from the switch.
This violates my understanding that the 220AC ground should NOT be connected to the bonding system. Now what????


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