If you've got a little tingle, then it sounds like the neutral wire _is_ bonded to ground (or shorted to ground) elsewhere in the system, and your lamp hasn't properly insulated its touchable metal pieces from its power.
Ground bonds usually don't see enough current to even register as a tingle, the ground-neutral potential on a bonded system will produce enough current to tingle, and the hot-ground and hot-neutral potentials on a bonded system will produce enough current to do a lot more than tingle. A chassis should never be bonded to a powered connection; that's why we have a third "ground" wire/prong (the green one). Current on the ground wire indicates a fault, and should cause some sort of alarm or disable the circuit where it happens (since the ground wire has resistance, so the existence of a current implies the existence of voltage between various grounded items). It sometimes happens on really old or defective equipment that we get a hot-bonded or neutral-bonded chassis, and most equipment with an unbonded chassis is designed to fail to a neutral-bond preferentially over failing to a hot bond (though any bond is still a failure since, as you mentioned, neutral is commonly considered to be _near_ ground potential, but not _at_ ground potential). Prior to the introduction of GFCI outlets, it was standard practice for bathrooms to have their power provided through an isolation transformer to break the neutral-ground bond. This meant that if someone in contact with the (normally neutral-bonded) water system were to accidentally come in contact with the hot conductor in an appliance, they'd only be exposed to a (very small) ground-bond current, instead of a (probably fatal) hot-neutral short current. Speaking of which, if you're really worried about safety, start by changing all the outlets on your boat to GFCI. That will do a lot to minimize the risk of electrocution, allowing you to focus more of your attention to safety on e.g. not starting fires or sinking the boat (speaking of which, the most common electicity-related peril I've seen on liveaboard boats up here in Toronto is overheating connections between appliances and extension cords--my first winter aboard, the folks two slips down had a fire start when the connection between an appliance and an extension cord overheated underneath onf of their cockpit cushions; always use adequately heavy cord, and always make sure that plug/socket connections are kept clear from insulating or flammable materials.) Cheers, Kris On Thu, Dec 09, 2010 at 11:44:54AM -0800, Eric T. wrote: > 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 > [email protected] > > ----- Original Message ----- > From: "Kris Coward" <[email protected]> > To: <[email protected]> > 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, [email protected] 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: [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 > >> > >> _______________________________________________ > >> Liveaboard mailing list > >> [email protected] > >> To adjust your membership settings over the web > >> http://liveaboardonline.com/mailman/listinfo/liveaboard > >> To subscribe send an email to [email protected] > >> > >> To unsubscribe send an email to [email protected] > >> The archives are at http://www.liveaboardonline.com/pipermail/liveaboard/ > >> > >> To search the archives > >> http://www.mail-archive.com/[email protected] > >> > >> The Mailman Users Guide can be found here > >> http://www.gnu.org/software/mailman/mailman-member/index.html > > _______________________________________________ > > Liveaboard mailing list > > [email protected] > > To adjust your membership settings over the web > > http://liveaboardonline.com/mailman/listinfo/liveaboard > > To subscribe send an email to [email protected] > > > > To unsubscribe send an email to [email protected] > > The archives are at http://www.liveaboardonline.com/pipermail/liveaboard/ > > > > To search the archives > > http://www.mail-archive.com/[email protected] > > > > The Mailman Users Guide can be found here > > http://www.gnu.org/software/mailman/mailman-member/index.html > > _______________________________________________ > Liveaboard mailing list > [email protected] > To adjust your membership settings over the web > http://liveaboardonline.com/mailman/listinfo/liveaboard > To subscribe send an email to [email protected] > > To unsubscribe send an email to [email protected] > The archives are at http://www.liveaboardonline.com/pipermail/liveaboard/ > > To search the archives > http://www.mail-archive.com/[email protected] > > The Mailman Users Guide can be found here > http://www.gnu.org/software/mailman/mailman-member/index.html -- Spent Casings Food, Fun, and Frolick http://fleshy.melon.org/cgi-bin/mailman/listinfo/fff-parties _______________________________________________ Liveaboard mailing list [email protected] To adjust your membership settings over the web http://liveaboardonline.com/mailman/listinfo/liveaboard To subscribe send an email to [email protected] To unsubscribe send an email to [email protected] The archives are at http://www.liveaboardonline.com/pipermail/liveaboard/ To search the archives http://www.mail-archive.com/[email protected] The Mailman Users Guide can be found here http://www.gnu.org/software/mailman/mailman-member/index.html
