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Posted: Tue Sep 08, 2009 7:16pm

Post Subject: Fitting RCD to inverter suopplied 230v AC ring main

I have just purchased an 1800 watt inveter. I have connected it up to my battery bank and tested it with a small load, and it all worked fine. However, when I used an RCD tester, the tester told me that the Live / Neutral wires were reversed, and to abandon the test. I treid to trip it anyway, which actually acheived nothing. I then tried my martindale tester, which told me the same about the live / neutral wire and said there was an earth fault. I sought the advice of an electrician freind and he said that as I was on a boat and it was afloat, I acrually did not have an earth path, because the boat was afloat and not connected to earth, even though I had an earth wires running to the engine bed and another from the casing of the inverter to another part of the engine room, a braket welded to the hull. It would appear that an RCD will never work properly unless I have an earth path and this requires being tied alongside, it will not work (nor protect) when I am moving. What can I do to make my inverter safe for operation, any help gratefully received! Peter


Posted: Wed Sep 09, 2009 8:06am

Post Subject: Fitting RCD to inverter suopplied 230v AC ring main

Dear Peter, The first thing you need to do is to WRITE to the inverter suppler and ask: 1. Can you fit a neutral-earth bond on their inverter. 2. If not how do you protect yourself with a RCD. 3. How will they indemnify you against damage or claims resulting from a 230V AC inverter system that can not be used with an RCD. I suspect your inverter's output are from a 115 - 0 - 115 voltage device so the line (brown cable) is running at 115V+ and the neutral at 115V-, giving 230v across the pair. Trying to make an "earth" on this type of inverter is likely to cause an expensive bang & smoke. The RCD will NOT work if the supply is from such an inverter however you tie up. It will work from a shoreline connection (assuming its suitably wired to the boat) even if the boat was floating free. The earth we talk about on boats is the metal hull. I am not qualified to advise on mains topics but from discussions elsewhere it seems this is a common problem involving "big name" equipment. In my unqualified state of knowledge I am far less worries about the safety of such inverter supplies than I am about shorelines that have no RCD and no earth to hull bond. I must advise that you seek the advice of a properly qualified marine electrician who is experienced in inverter derived mains supplies. Tony Brooks

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