See Annotations Below Norm S/V Bandersnatch Lying Julington Creek FL N30 07.68 W081 38.47
----- Original Message ----- From: ahmet erkan To: [email protected] Sent: 12/20/2010 11:04:05 PM Subject: Re: [Liveaboard] GALVANIC ISOLATOR Hi Norm, I am not sure if your questions have already been answered by the list but let me make an attempt anyway. You asked : "would you please address the issue of connecting (or not connecting) the ac neutral to earth." IMO not connecting the ac neutral to earth would make the electrical system safe for the user making accidental contact with a hot conductor. However if the user begins to ignore the basic safety rules and becomes complacent about touching hot conductors he/she will be at the mercy of the system being fault free. Therefore a system with an isolated neutral ought to be checked frequently (preferably automatically) to verify all the current carrying conductors are indeed isolated from the chassis. Another shortcoming of the ungrounded neutral is you cannot use GFCI circuit breakers. One other shortcoming may be the increased vulnerability of your electronics to lightning. The isolation transformer that is providing the floating secondary neutral should be shielded (preferably both primary and secondary shields) and the shields should be hardwired to earth. Norm - Yes, I agree (and stated) that a way to check for ground faults would be a Good Thing. Even a simple light bulb or meter. There is a shield on my isolation transformer between the windings and it is grounded to ship's ground. I did try using a GFCI on the engine room circuit but the environment in the ER was too damp and it wouldn't hold. I have not tried it elsewhere but I don't know why they wouldn't work. Even though the neutral is floating (on my boat), all the non-current carrying metal parts are still grounded. >From what I understand about lightening damage it is small voltages inside >sensitive electronics induced by the nearby heavy current flows from >lightening that does the most damage. You asked : "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." Correct, except I have never seen a jumper wire. The panels usually have a long aluminum block bolted to the chassis and it has a bunch of screw terminals for both neutral and ground wires. US house wiring code requires both neutral (white) and ground (green) wires to be terminated to the chassis of the distribution panel/circuit breaker box. The chassis of the distribution panel is also routed (with a green wire) to a ground rod or a buried water pipe. I remember some Canadian folks on the list freaking out when they heard white neutral and green ground wires are bonded at the chassis of the panel but this is the way it is, and it makes sense to us. Norm - My memory (such as it is) tells me that the neutral terminal block in the US is insulated, the grounding block not insulated, and there is a wire connecting the two. But I have made a note on my "To Do" list to have a look in a breaker box the next time I am in Lowes or Home Depot. You asked : "I seem to have read that the European electrical system has ungrounded neutrals. Is this true or not?" In Turkey the houses are wired to one phase of the 220V Wye pole transformers with a pair of copper wires. One wire is hot and it has insulation, the other wire is the neutral and it is a bare copper conductor. The bare wire is bonded to the steel pipes that bring water to the house. The metal surfaces of the appliances are bonded to the bare neutral with a jumper and this jumper may be opened by the electrician to test the appliance for leakage. I believe the newer houses are using an insulated neutral and a bare ground wire so that GFCI devices can be used. The chassis to neutral jumper on the appliances are removed to be able to use the GFCI devices in bathrooms. Cheers Ahmet Norm - Thank you for the great information about how it is done in Turkey. It sounds safe to me and I'd bet Dr. Oz would approve it too.
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