Just plug any lamp qith a 2 wire cord (actually called 'lamp cord!) into a power source that does NOT have neutral connected to ground and the "tingle" you get when you touch the metal parts of the lamp will convince you that it is A SAFETY ISSUE. tHE NEUTRAL LINE IS COMMONLY CONSIDERRED TO BE NEAR GROUND POTENTIAL. bAD DESIGN? yEP. cOMMON? yEP!
Eric Thompson S/V Procrastinator South San Francisco capteri...@sbcglobal.net ----- Original Message ----- From: "Kris Coward" <k...@melon.org> To: <liveaboard@liveaboardonline.com> Sent: Thursday, December 09, 2010 11:28 AM Subject: Re: [Liveaboard] GALVANIC ISOLATOR > > Personally, I'd be strongly disinclined to bond neutral to anything on a > boat. Unlike ground lines, neutral lines are supposed to be carrying > current as a matter of normal operations. Since the lines aren't > superconductive, there is resistance, so there will be voltage between > points on the line. So if something neutral comes into contact with the > water, there will be an AC voltage between it and whatever neutral's > been bonded to. Supposing that the bond is to the engine (or in the > case of a metal boat, the hull), half the time, the prop shaft will have > a positive voltage relative to the accidentally submerged "neutral". > Noting also that losing up to 10% of voltage in transmission is > generally considered acceptable, this could be as much as 12Vrms on a > 120VAC system. So this will corrode the prop shaft that half of the > time, and pretty soon the stuffing box is going to be irrecoverably > leaky and the boat may sink (I don't think I even need to talk about a > hull bond here). > > This isn't as much of a problem with a DC system, because the > engine/hull/etc. get bonded to the negative side of the circuit, and > negative potentials accumulate metal rather than corroding. You're still > going to be screwed if the positive side of the DC system gets shorted > to the sea via, say, a through-hull, but it you have a line or a device > that just gets submerged (e.g. a leak/short gets formed in the depth > sounder, or the knotlog impeller) you just lose the wire/device (which > it's pretty safe to assume would happen anyway, since the damned thing > fell in the drink already). > > Now some of you are probably wondering about the half the time that the > AC system would give the engine/hull bond a negative voltage; wouldn't > that deposit back the metal that got corroded off when it was positive. > Well sure, sort of. Of course the metal that gets accumulated back to > replace the corroded metal won't necessarily be the same metal that came > off (after all, in salt water, there's all that sodium kicking around, > so what are the odds that all the ions sticking to the shaft and turning > back into metal as they get electrons from the bond, are going to be > from the bronze/stainless/etc. that you just sloughed off). On top of > that, your metal will completely lose any temper that it had, and has a > decent chance of ending up all spongy and brittle. So even if your prop > shaft doesn't dwindle down to the thickness of a toothpick, there's a > good chance that you'll be able to just plain snap it in half after a > while (ditto for metal hulls, and wouldn't that ever suck). > > So unless someone can give me a really compelling reason to bond my AC > neutral, I'll be keeping those lines ungrounded, and solidly > mechanically seperated from any machinery, through-hulls, etc. that > might carry current to the water if shorted to either of the lines. (And > if you didn't pick it up from what was mentioned above, it's also a > really good idea to keep your positive DC wires the hell away from > anything like that too, lest they get shorted to some (through-)hull.) > > Cheers, > Kris > > On Wed, Dec 08, 2010 at 11:05:56PM -0500, banders...@earthlink.net wrote: >> 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: liveaboard@liveaboardonline.com >> 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: liveaboard-boun...@liveaboardonline.com >> [mailto:liveaboard-boun...@liveaboardonline.com] On Behalf Of Emory Jones >> Sent: Wednesday, December 08, 2010 4:30 PM >> To: liveaboard@liveaboardonline.com >> 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 >> >> _______________________________________________ >> Liveaboard mailing list >> Liveaboard@liveaboardonline.com >> To adjust your membership settings over the web >> http://liveaboardonline.com/mailman/listinfo/liveaboard >> To subscribe send an email to liveaboard-j...@liveaboardonline.com >> >> To unsubscribe send an email to liveaboard-le...@liveaboardonline.com >> The archives are at http://www.liveaboardonline.com/pipermail/liveaboard/ >> >> To search the archives >> http://www.mail-archive.com/liveabo...@liveaboardnow.org >> >> The Mailman Users Guide can be found here >> http://www.gnu.org/software/mailman/mailman-member/index.html > _______________________________________________ > Liveaboard mailing list > Liveaboard@liveaboardonline.com > To adjust your membership settings over the web > http://liveaboardonline.com/mailman/listinfo/liveaboard > To subscribe send an email to liveaboard-j...@liveaboardonline.com > > To unsubscribe send an email to liveaboard-le...@liveaboardonline.com > The archives are at http://www.liveaboardonline.com/pipermail/liveaboard/ > > To search the archives > http://www.mail-archive.com/liveabo...@liveaboardnow.org > > The Mailman Users Guide can be found here > http://www.gnu.org/software/mailman/mailman-member/index.html _______________________________________________ Liveaboard mailing list Liveaboard@liveaboardonline.com To adjust your membership settings over the web http://liveaboardonline.com/mailman/listinfo/liveaboard To subscribe send an email to liveaboard-j...@liveaboardonline.com To unsubscribe send an email to liveaboard-le...@liveaboardonline.com The archives are at http://www.liveaboardonline.com/pipermail/liveaboard/ To search the archives http://www.mail-archive.com/liveabo...@liveaboardnow.org The Mailman Users Guide can be found here http://www.gnu.org/software/mailman/mailman-member/index.html
