Ah, Arild! Now, you are really taking me to task here! But, I must apologize, and defer, as I don't have the time nor inclination to debate these issues. You asked a few questions and I responded, briefly, with my thoughts. But that's all they are and I don't wish to justify them. I have no quarrel with progress and innovation, but much of it flies in the face of KISS and convention, both of which are favorites of mine because they are always less expensive and usually more dependable. Best, John "Seahorse" in the swamps of Cape May, wishing for Sun! In a message dated 10/11/2005 4:50:39 P.M. Eastern Daylight Time, elnav@uniserve.com writes: Quoting Truelove39@aol.com: > I think there are several problems with this system. This is a DC system, > right? > > 1) Electrical systems are designed and constructed so as to limit the power > available >>>>>>>>>>>>. snip<<<<<<<<<<< > With small loads (lights, etc.) being supplied via short runs of small > conductors from adjacent large ones, the inrush current will be large, > shortening, for instance, bulb life. It's been reported that switch failures happen, as well. REPLY A properly designed and installed system doesn't do that! At least mine doesn't. > > 2) If this large DC bus runs the length of the boat, it will create a > substantial magnetic field, unless the conductors are twisted, possibly > affecting the autopilot compass. REPLY The magnetic effect is no different than if the same amount of current is drawn through numerous individual circuits running in parallel. > 4) A fault on this bus will disable the whole electrical system. REPLY And why would a fault be more likely on large conductors than a bunch of smaller conductors? > > >>>> snip <<<< > Utility grids are not appropriate examples > of electrical power distribution systems on boats, as they are high-voltage > interconnections between power plants and sub-stations, usually consisting > of 3 phases - no neutral is used as current-carrying conductor. At any rate, I like centralized distribution. REPLY Why would a distribution system not be a suitable example? You have a power source, generator or alternator, and a load. Voltage and current simply dictates what amount of insulationand conductor size is required. The principle is the same. Your mention of 3 phase doesn't make a difference to the concept. When dealing with a substationand the end user being aresidence with a split phase, then a neutral wire is used. But that is not relevant. To use your own comment about centralized distribution, that would mean that all your circuits in the house would have a breaker down at the sub station not at your house. Not too practical. The original post refers to a "3 wire" system with the third wire being the communications link that provides the control signals to individual devices. This is exactly what is now used in many automotive applications. This communications link can be hard wired and relays are used to operate a circuit. Examples of this are your bow thruster, anchor winch and in some cases remote operated search lights. If you go to AC circuits you c an add garage door openers. security gates and so on. The original X-10 system used the power wiring itself for the control signal channle link but technical limitations in DC circuits meant that a third wir ehad to be added. Relays are on of the oldest methods but by no means the only one. I have seen numerous example of cottage applications wher you can phone your cottage to turn on the heat several hours befoer you arrive at the cottage or ski chalet. Thsi uses telephone networks as the comm link. Moer recently we have seen Blue tooth linked devices doing similar things. You can monitor your yacht home or whatever using internet communications and PC cams or mikes to look and listen to what is going on remotely. A simple circuit can also turn on/off lights etc. Regardless of voltage or current flow the concept is pretty much the same. Details will differ only as far as technical requirements dictate. In a previous life I worked with SCADA equipment. Simply by touching a computer screen ( touch screen) I could connect or disconnect a 2 megtawatt transformer station connected to a 220,000 High voltage line and its output was 27,6000 volts. In that station we monitored 400 points and controlled 68 switches. Pretty small compared to the province wide system used by Ontario Hydro which controlled the entire province including several nuclear power stations from one central control room and which was linked by microwave, telephone, and fibre optic communication links to these individual switch points. But on the small end of the scale, I have also done tiny systems which only controlled 50 light circuits inside one 40 foot long custome coach RV. Scale varies but the concept and principle remains the same. Cheers Arild