----- Original Message ----- From: Harold M Hallikainen To: Sent: Monday, March 19, 2001 11:27 AM Subject: Re: [OT]: Four-wire electric distribution system > On Mon, 19 Mar 2001 06:18:14 -0500 Bob Ammerman > writes: > > On the other hand, next month I am installing an overhead 100A > > feeder to run > > from one building to another at a campground where I volunteer , and > > the > > inspector has explicitly said that it is ok to run only a single > > conductor, > > rather than separate protective ground and neutral. This is, of > > course, in > > violation of the National Electric Code, but very common in rural > > areas. > > > > So, the return current is passed through the "local earth" (such as a > water pipe)? And if there's a 1 ohm resistance to ground, all the water > faucets are 100V above ground? No, unless the neutral conductor is grossly undersized. At most you would have about a 10V drop across the neutral. There _IS_ a neutral conductor, sized the same as the phase conductors, but there isn't a _separate_ protective ground conductor as required by code. Here is a summary: From the pole (power company property) to the house/building: 2 phase conductors sized for entire load 1 neutral/ground conductor typically same size as phase conductor. In the 'service entrance panel' of the building: The incoming neutral/ground conductor connects to two separate busbars in the panel, one of which is treated as the protective ground and the other as the neutral. In this box, and only in this box (according to the code) the two are connected together. In addition, separate earth ground conductors are run from the service entrance panel to the local water pipe, gas pipe and a ground rod. All other connections are then supposed to be four wire: 2 phase conductors (often black and red) 1 insulated neutral (usually white) 1 uninsulated protective ground In rural areas the uninsulated protective ground is often omitted on runs to outbuildings and then the 'service entrance panel' in the outbuilding is set up the same as the 'service entrance panel' of the main building (two separate busbars - tied together, plus earth grounds to water pipes, ground rod, etc.) In urban/suburban areas you generally have to run a four wire to the outbuilding. In this case the two busbars in the service entrance panel are not bonded together, although the protective ground is connected to water pipe, ground rod, etc. Even in urban/suburban areas many old (grandfathered) installations use a simpe two wire (hot and neutral) or three wire (two phased and neutral) overhead connection to garages and the like. Again, there should be a 'protective ground' established at the garage. Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics