<banders...@earthlink.net> writes: > 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. ------------------------------------ The answer to the above is "It depends"<G>.
In the USA, most residential buildings are supplied 120/240V/1PH/60HZ, known as the classic "Edison circuit". A 240VAC single phase x'fmr is center tapped and tied to earth ground at the center tap providing a 240VAC phase to phase (L1-L2) circuit and two (2), 120VAC circuits (L1-N and L2-N). The grounded center tap insures that the max potential referenced to ground will not exceed 120VAC. In certain parts of the rural SouthWest, the utility distributes 240VAC/3PH/60HZ power. To obtain 120VAC, they center tap one phase to obtain the 120/240VAC Edison. The above is known as "Wild Leg Delta" and can cause some interesting problems, if not careful. Fortunately it is about gone. Next you have 208Y/120VAC/3PH/4Wire/60HZ "Y" which is quite common in light commercial applications such as shopping centers. The transformer windings are connected in a "Y" configuration and the center tap is tied to earth ground. This configuration provides a 208VAC/3PH/60HZ supply for 3PH loads and also three (3), 120VAC circuits (L1-N, L2-N and L3-N). Again, the grounded center tap insures that the max potential referenced to ground will not exceed 120VAC. Next you have Europe, much of which uses 380/220/3PH/4W/50HZ "Y". This is also a 3PH/4W system which also has the center tap grounded. Most 1PH loads in Europe are 220V/1PH/50HZ Back to the USA. Two (2) other common distribution voltages for industrial applications are 480VAC/3PH/3W/60HZ delta and 480/277VAC/3PH/4W/60HZ "Y". Again, the grounded center tap insures that the max potential referenced to ground will not exceed 277VAC. Not much residential application for any 480VAC configuration. Hpoe this helps explain what can be a little confusing. Lew _______________________________________________ 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
