This has become an issue of debate here in teh office so I thought I'd ask the public. What is the standard voltage for domestic supply in North America? I've heard anything from 110V to 125V, and I've measured it at anywhere from 115 to 122 so what is the "official" standard?
I don't know what the legal requirement is but when designing products all companies I have worked for design for 120+/- 15% or 102 to 134Vac. Generally when measured the voltage is in the 120s.
"Anything from 110V to 125V" is probably close. Expect variability. Japan uses a nominal 100V at 60Hz, so if you design for 90V to the North American maximum you could theoretically sell into Japan.
I just measured 119.5VAC, about 40' from a two-house step-down transformer (which is the usual method in this area for underground electrical distribution).
...Jim Thompson
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| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
In the United States ANSI C84.1 says our official household voltage should be 120V +/- 5% under normal circumstances, with somewhat worse tolerance for short duration in the case of unusual circumstances. Not all utilities will necessarily always fully comply with the standard in all locations however, so it would probably be wise to design products for a somewhat larger tolerance band.
Back in the late '70's, when I was designing switchers for GenRad's portable testers, I could accept any input from 90VAC-288VAC and automatically adjust for it ;-)
...Jim Thompson
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| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
There are all sorts of voltage adjusters, boosters, transformer taps, etc downstream from the nearest substation (as well as upstream), to keep the voltage within a reasonable range. It will vary as much as 5-10% due to load conditions and main generator variations. There is no way to be assured of any exact voltage at your point of use, short of an individual voltage regulator.
Your comment on light bulbs reminds me that my father told me, long ago, you could take a burned out light bulb to the Baltimore Gas and Electric company and they would give you a new one. After all, it was *their* electricity that burned it out, and the sooner you got a new one, the sooner you would be using more of their product. In those days, it might not be unreasonable for someone to go back to their kerosene lamps for awhile, and you might not be able to buy a new bulb es easily or cheaply as today.
I wonder what is the effect of higher voltage on the longevity of more efficient screw-in fluorescent bulbs? I have largely switched over to them, and only one or two have burned out over a couple of years.
I live in a rural area where the voltage fluctuates quite a bit. When we first moved here we replaced every incandescent light bulb at least once in the first year. We started replacing them with compact fluorescent bulbs and we haven't had to change one of those yet in the 4 years we've been here.
It's on the list of things to do to understand why this is but I've never gotten around to it.
It is also interesting to look at the standard voltages as you go up from low voltage to medium and high voltage. For single phase, the standard seems to be 120/240. For three phase, it is 120/208. There is also 240 V three phase, which would have 138 VAC Phase to neutral, but this is rarely used. Then 480 V three phase, which is 277 VAC phase to neutral. The 277 is often used in lighting circuits. You sometimes see 416 VAC (208*2), and there is also some 600 VAC, which is the limit for "low voltage".
I have also heard that power sources are rated higher, as 240 or 480 VAC, while the equipment that uses these sources is normally rated lower, as 220,
230, 440, or 460. It may also apply to 120, 115, and 110. It is interesting, however, that I have never heard of anything other than 208 VAC for that type of three phase, even though it typically varies from 200 to 216 VAC.
In the medium voltage area, from 600V to 5000V, very common voltages are
4160, which is 208 * 20, and also 2400, which is just the line-to-neutral of
4160. There is also 4800 V, which is about the limit. These are all based on ratios of 2, 4, and 5, as well as, of course sqrt(3) to convert L-L to L-N for three phase. Medium voltage is commonly used for high power motors and generators, and for residential and small commercial and industrial distribution lines, in cables and overhead.
I don't know as much about standards for high voltage AC. I think 13.8 kV and 14.4 kV are fairly common, and possibly 57.6. Of course, these are also the same numbers as common baud rates! I think 100 kV or 120 kV is also common. The really big transmission lines I think are in the order of 500kV,
750kV, 1MV, and maybe up to 2MV or so.
Many long distance transmission lines are now DC, because of about 50% better efficiency due to less radiated emissions and impedance losses. There are some interesting articles on the effects of having a high voltage field of DC with respect to the earth, where there is a constant "wind" of ions traveling from one conductor to another. There are supposed health benefits from negative ions, and feeling of impending disaster from positive ions (which is evidenced just before lightning storms in behavior of animals, including people). This strays a bit from the original question, but it is a matter of interest.
The actual conversion from AC at the generator, to DC for transmission, and back to AC for distribution, is also interesting.
The problem with incandescent bulbs is that they are very inefficient (at creating light) at lower voltages. They are, however, almost 100% efficient at creating heat. So, incandescents are OK in the winter, as they are just another heat source. The color of the light also changes with voltage, which may or may not be desirable. Compact fluorescents are much more efficient, and are now very low priced. They seem to last much longer, and are probably more tolerant of higher voltages. Their drawbacks are mostly their harsher bluish color, and they don't work as well in cold temperatures.
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