Ahoy Al, I understand the wisdom of connecting all the touchable metal parts of electrical equipment to ship's earth so the bilge water and all touchable metal parts will be at the same voltage as the earth and I do this on my vessel.
It is also a good idea to have a way to measure the ac voltage/current between the grounding (green or bare) wires coming from your system, and the grounding point to which you attach them, so you can be aware of any leakage. But would you please address the issue of connecting (or not connecting) the ac neutral to earth. For example, my 240 vac loads (and those ashore) have no neutral. Why should 120 vac loads be any different? Wouldn't it make things safer to isolate *all* current-carrying conductors rather than connect neutral ( a current carrying conductor) to the ship's hull or other similar earth-like structure? I seem to have read that the European electrical system has ungrounded neutrals. Is this true or not? I believe in the US power that comes into a house is from a center tapped secondary winding in the pole transformer which delivers 240 vac at the ends of the coil and the neutral comes from the center tap. The grounding of the neutral is only added in the house's breaker box by the neutral/grounding jumper wire. Correct me if I am mistaken. I have had an ungrounded neutral 120 vac system for 30 years on an electrically powerful and complex vessel and have never felt the slightest tingle. I did this mainly because that was the way they did it on the many merchant marine ships I served on and because I believed the safety aspects of this scheme would work just as well on my own vessel. Norm S/V Bandersnatch Lying Julington Creek FL N30 07.68 W081 38.47 ----- Original Message ----- From: Al Thomason To: [email protected] Sent: 12/8/2010 9:03:06 PM Subject: Re: [Liveaboard] GALVANIC ISOLATOR Hi: OK, in short I think there are two questions here: 1) Connect the onboard AC safety ground to the onboard DC Ground point: Yes always. There has been several articles over the years on people dying when swimming around a faulty boat w/o this connection. ABYC requires it. Some will complain that this can cause issues with stray current and galvanic issues, but bottom line: This bonding is a major safety issue, the other concerns can be addressed below. And more so, if something does go very very bad, and you do not have this on your boat can cause lots of problems for you. Here is an article of a local boy who died as a direct result of the boat not having this connection and a fault occurring: http://www.abycinc.org/lucas_ritz.pdf 2) Connecting of ships AC Safety Ground to Shore Safety Ground.: There are basically two ways to do this: 1) make the connection via your shore power cable - use of a galvanic Isolator can help reduce some of the stray current concerns here. And 2) use a true isolation transformer. In this case, the shore safety ground is only connected to the shield in the transformer, and then a new bonding point is established by connecting the ship safety ground and ship neutral onboard (and after the isolation transformer). This approach will remove almost all issues with stray currents. This is not really that complex of a topic, though some folks like to poke at #1 and cause confusion. Note also that the above might be modified some for non US boats (e.g. EU boats). I am just not sure the best practice for them and the AC system can be slightly different then the US system. (Beyond 120v/60hz..) Good luck! -al- From: [email protected] [mailto:[email protected]] On Behalf Of Emory Jones Sent: Wednesday, December 08, 2010 4:30 PM To: [email protected] Subject: Re: [Liveaboard] GALVANIC ISOLATOR Thanks to all who responded! There does not seem to a consensus in regard to the AC ground. Any other (additional) discussion would certainly help to educate me. I am concerned about an AC to DC connection however my fears may be ungrounded (sorry I couldn't resist). Thanks again for all the input. Emory Jones S/V Jacob Andrew Solomons, MD
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