>"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."
With a "floating Neutral", the GFCI is going to detect a current from hot terminal through a person to earth and trip open only if the neutral insulation has also broken down to ground, similarly GFCI is going to detect a current from neutral through a person to earth and open only if the hot line insulation has also broken down to earth. (I believe Norm has also said this in different words) If one wants to use GFCI devices with a floating Neutral, I suggest he/she (so PC) connects a 1uF capacitor from the hot line to ship's ground and another 1uF capacitor from the neutral to the ships ground. Both capacitors should be connected to the line side of the GFCI device. (ie: at the 120V secondary of your shielded isolation transformer preferably close to the transformer for noise attenuation purposes) "60V is safer than 120V" in fact the 48V used by the phone company is actually the terminal voltage of a 48V rated battery that is typically at 55V and could go to 60V during equalize. At the phone company we routinely worked on the 48V live equipment and touched the negative terminal (positive terminal is grounded for galvanic corrosion prevention) without worrying about getting electrocuted. So there you are, a +/-60Vac ships system with a GFCI protection device that will trip if there is more than 5mA imbalance between the hot or neutral currents and a little safer than your floating Neutral system. The imbalance will occur and interrupt the circuit either during a "heavy wet contact" by the user or if there is a fault in the system. The GFCI used in a grounded neutral system cannot detect Neutral to Ground type ground faults reliably due to lack of a supply to drive the current but the +/- 60V system should detect either Hot to ground or Neutral to ground insulation failures equally reliably. (Do test anyway) The capacitors should also work in tandem with the shield during lightning storms and provide common mode attenuation to voltage spikes in the order of 120dB. The capacitors should also work in tandem with the leakage inductance of the isolation transformer and provide normal mode attenuation to voltage spikes proportional to frequency of the disturbance. Again, test for proper functionality of any system before relying on it for safety. This method of wiring is just a paper design at this time and has not been verified, I can verify using my isolation transformer and a GFCI receptacle or a CB from Home Depot and provide the results to the list if anyone wants to implement it? BTW who is Dr. Oz? A friend of George Orwell? I learn so many things on this list. Fair winds S/V 8827 Ahmet From: [email protected] To: [email protected] Date: Sat, 25 Dec 2010 17:13:30 -0500 Subject: Re: [Liveaboard] GALVANIC ISOLATOR 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. _______________________________________________ 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
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