You then have a very "hot" DC system, and potentially dangerous surrounding water. This may not generate enough current flow through the DC ground (water) to trip the shore or boat RCD and without the connection has no other means of returning to earth. The RCD is still able to sense the difference in current between the live and neutral, so can trip.Ĭalder's and presumably the American argument for using the AC earth to DC negative connection includes the scenario where you may have an AC leak into the DC circuit (eg. My understanding is that the GI does not "disconnect" the RCD - it simply provides a safe return to earth of leaked AC. The voltage at which it closes is determined by the number of diodes. When there is a voltage leak it is designed to close/conduct thus providing person protection. The GI is designed not to conduct under normal circumstances (unless it has a capacitor allowing small AC current flow - your "fault current") thus providing galvanic protection. I think the point about the RCD is that there is a reported failure rate of (I think) 10 - 20% on testing. In my experience its often found that there are significant fault currents in the earth circuit, this can cause a GI to close, effectivly nullifying their existence. Its worth pointing out that a Galvanic isolator in effects basically disconnects that anyway. I for one am not in favour of connecting the protective earth ( misnamed AC ground) to the DC negative, provided a whole boat RCD is fitted. Although the boat is fitted with a RCD as well as the pontoon they could both fail. Im not saying that the system is 100% safe. The only thing that is connected to the boat anode is the Engine and shaft. I also test the RCD every week or so and use a plug in mains tester just to ensure that connections are ok. I check regularly that the wires are fastened in place and that they are not rubbing on anything. I was thinking that the system would be earthed with a GI but on inspection it is fairly similar to our previous boat, socket in the cockpit, RCD in the cockpit locker and then wires running through the boat to everything. Our current boat has an electrician fitted system, which feeds things like the mains sockets, calorifier, battery charger etc. Our previous boat had a simple shorepower system with a socket in the cockpit, RCD in the cabin and then a feed from the RCD to a few sockets. If someone was to say there is no need to connect to the anode, and then a mains wire rubs through a metal deck or hull fitting the whole boat would become live, the RCD could fail and you could be killed.Ĭonnecting the AC to the DC anode connection then involves the risk of galvanic action and eat away at your anodes and then move onto things like the prop and shaft but then it would be safer than not connecting.Īt the same time, if you dont connect the earth up this gives a risk. I agree with what Jegs states about litigation etc.
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