Tom Székely, P.E., LEED AP

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July 29, 1991

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Occam's Razor

"Entities ought not to be multiplied, except from necessity." has come down to us from 14th century England as the KISS principle. (Keep it simple, stupid.) All well and good, but to what should the striving for simplicity be directed? 220 to 240 volt true single phase is not the same as the 208 volt "single" phase of construction industry jargon, but what's more important; the fact that the former is generated differently from the latter, or that the latter is 18 volts less than the lower bound of the former? (What'd he say?)

Well, boys and girls, a single phase motor has two leads that don't care whether they're fed from two ends of one transformer winding or two ends of two series connected windings. (How's that again?) 230 volt (or 230/460 dual voltage; 220 volt motors and 220/440 dual voltage motors haven't been around since 1965) motors are so designated because they're built to standards that ensure their operation on voltages within +/- 10% of nameplate voltage, or 207 to 253 volts, which encompasses the 220-240 volt single phase range rather comfortably. The 207 volt bottom end doesn't leave a great cushion for motors on a 208 volt system, especially when it's considered that codes permit a voltage loss in the distribution system of as high as 5 %. A motor on such a system could see as little as 198 volts at its terminals.

Electrical resistance is an essentially constant quantity in a circuit, regardless of the impressed voltage. Electrical reactance, on the other hand, owing its very existence to change, is trickier. Crank down the voltage on a light bulb, and its constant resistance lets less current flow, and the lamp bums less brightly, lasting a lot longer in the bargain. Do the same with a motor and it draws more current, not less, and is liable to burn out if even only normally loaded. If you really live right, it could start a fire in its feeder circuit. Circuit breakers and fuses are pretty good on short circuits, but lousy on overloads. The two are not the same. (Where have I heard that before?) What's a designer to do? Specify 200 volt motors for use on 208 volt systems. It's why they're made. Better yet, call your friendly neighborhood consulting engineer and was made.

Conventional Wisdom Isn't

About 15 years back, when [expensive, mainframe] CAD systems began to make substantial inroads into what I call "second-tier" heavy industrial design-build outfits (i.e., the guys one step down from Bechtel, Fluor, et al), all of us hotshot designers looked upon the CAD drafted reference drawings we began to receive with a mixture of smugness and disdain. After all, everyone knew that though a CAD system might make revisions easier, there was no way anyone could lay down an original drawing by computer faster than we could by hand.

Boy, were we wrong.

The thing that continues to amaze me is how many people use a variation on this theme to avoid doing things differently from their wont. I have walked into so many design offices that are frozen in the 1970's, or even worse, that bought the tools of the 80's and 90's and are using them with a 1970's mind-set, that it scares me.

All right, so you've sprung for this computer, and it’s pretty neat for writing letters, and dynamite for specs. So why are you still doing zoning calculations by hand? In the 1970's, to do any sort of calculations on a computer, it was required you learn a language such as Fortran, something that could easily eat up 50 to 100 hours of your time. Then you'd be in the position of shooting another 50 to 100 hours to write and debug your first application. Today, with the tutorial that comes with any decent spreadsheet, gosh, it'd have to take you at least 8 to 10 hours to learn enough to set up your zoning calculations, and probably another hour (maybe two) to do it. I'm not even going to get into relational databases, which is how this missive finds its way to you (and billing to my paying customers).

Didja know that spreadsheets allow you to set up look up tables in them to, for example, select the correct conduit and wire size after doing electric code demand calculations? Didja know you don't need a degree in computer science to do any of this? Didja know you don't have to be a member of the Society of Automotive Engineers to know how to drive a car?

Oh, what's that? You say you were convinced long ago, and would really take the plunge, but it's so damned expensive. Yeah, I just bought an HP compatible 6 PPM laser printer, outfitted with 2.5 meg of RAM and a 65-in-one font cartridge for 575 bucks.

Don't let it get around, but PC prices have been in free fall since IBM decided to follow the Apple II into open architecture back in 1981.

Back Up Two Steps

The dangers of operating motors below rated voltage do not obtain in the case of resistive loads such as lamps or electric heat. As a matter of fact, operating 130 volt lamps (There are such things, and they should be specified if you just have to use incandescent lamps which are in hard to reach places.) on a 120 volt system will extend their life by better than 40%, while consuming 85 % of their rated power and delivering 75 % of rated light output. A similar thing happens when using a 230 volt electric range on 208 volts, with its power (heat) output reduced to 82 % of its nameplate rating.

Lighting and Efficiency

Lamps in general use fall into two broad categories; filament or incandescent lamps, comprising quartz and (most) sealed beam lamps, and gas-discharge lamps, comprising fluorescent (N.B. the spelling; these lamps are not milled from grain) mercury vapor, HPS, LPS, etc.

Front to back lamp efficiency expressed as a percentage of visible light power out for electrical power in, is pretty depressing. For incandescent lamps, it's about 10%, for fluorescents, for mercury vapor (gotcha) only 15 %, metal halide 24 %, high pressure sodium 30%, and low pressure sodium 35%. For all lamps except incandescent, the numbers are not as "good" as they seem, for ballast losses have not been taken into account.

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