Frankga123

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Mains electricity vs. incoming line current

Hello Frankga123, and welcome to Wikipedia. Your reference book is not primarily about electrical distribution and seems to have confused three-phase and split phase distribution methods. You quoted the following:

"Electricity is usually supplied to buildings in the United States by 60 Hz alternating current with a nominal rms of 200-240 volts. These are termed nominal because, as users operate various resistances, the voltages constantly fluctuate, as illustrated by Ohm's law. This power is called the incoming-line current (sometimes called the mains) and is supplied in the form of a three-phase power cycle(Figure 5-4). One of the "hot" wires is alwasy half the incoming voltage above-ground potential, while the other is always the same voltage below-ground potential. In the United States each carries 110-120 volts. With 60 Hz alternating current, the two hot wires reverse their polarity 120 times per second. Bringing incoming line current from the neutral (or ground) wire and one of the hot wires produces a potential difference of 110-120 volts. Because the two lines are not in phase with one another, using incoming current from both hot wires produces a potential difference that is less than the sm of the two single phases. The usual result is about 210 volts. Nearly all x-ray equipment operates from an incoming line of 210-220 volts."

Richard R. Carlton, Arlene McKenna Adler (2000). Principles of Radiographic Imaging: An Art and a Science. Thomson Delmar Learning.

This passage needlessly confuses power and current. It would have been more accurate if it had said that large buildings in the United States often have 120/208 V three-phase power distribution, allowing large loads (such as X-ray machines) to be connnected to two of the phases for 208 V. Smaller buildings, such as most homes, and many small commercial buildings, have 120/240 Volt single-phase three-wire supplies, with the center tap of the transformer connected to ground; connecting across the two energized wires gives 240 volts, and from either "live" wire to the neutral gives 120 volts. X-ray machines should be built so that they can be connected either to a 208 V supply or to a 240 Volt supply.

I also find the style of that paragraph to be confusing, with a side reference without explanation to Ohm's Law as if that cleared anything up for the reader. I hope the rest of the text is more clear than this passage. (It probably is...non-electrical writers often get the electrical parts wrong, I don't know why, it's not rocket science.)

The expression "incoming line current" isn't usually used, in my experience, to describe the power system. In most cases, it's better to find an existing Wikipedia article and improve it, instead of starting a parallel article under a slightly different title. If a phrase is very commonly used, so that someone looking for the subject matter would type it into the search box, you can create something called a "redirect" that would point the reader to the relevant article. This saves storage space for the encyclopedia, not so much a problem for the on-line version but important if a meaninful subset of Wikipedia articles are to be sent on a DVD or CD.

Everyone was new to Wikipedia at some point - this is soon cured if you spend enough time at it.

--Wtshymanski (talk) 13:38, 8 October 2008 (UTC)