Tom Székely, P.E., LEED AP

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June 28, 1991

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Ingenuity and Risk

Engine, the root word of engineer, comes to us from the Old French engin("ingenuity"), which comes in turn from the Latin ingenium("natural capacity"). By Middle French's ingeniux ("ingenious") the European cognate for engineer (e.g. the Ingenieur of Modern French) was firmly locked into ingenuity as a character trait.

We, alas, seem to have lost the connection between engineering and ingenuity in more than just words

How many times have we heard an expert tell a layman all the reasons a request could not be fulfilled. Is that why engineers should be engaged? I think not. Understand, I'm not saying we can repeal the laws of Physics, but, if an engineer is reluctant to try something because no one he knows of has done it before him, why did he become an engineer in the first place?

In some segments of industry, the metaphor has arisen that you can tell the pioneers by the arrows in their backs. In the construction industry some will defend their lack of vision by telling you the pioneers can be identified as the ones in court.

I (with acknowledgement to Marvin Harris for the terse answer) disagree. I believe that what conflict exists comes more from miscommunication which leads to unfulfilled expectations than from any inability to execute in the field, innovative ideas from the design office.

You Can't Have All the Answers When You Don't Know the Questions

One would think that with all the technical catalogues and manufacturer's representatives out there, doing something as mundane as low voltage lights in a fountain would be a fairly straightforward task. At least, that's what I thought.

Wrong again.

300 watt sealed beam lamps fed from individual 300 watt transformers must have their place, but it isn't in pointing straight up through water 6" deep. Sealed beam auto headlamps at 75 watts, wired to be on hi-beam did very nicely, but the thought of hanging 4 lights on each transformer with the concomitant increase in wire size to keep voltage drop within limits galled me.

Where is it written that 3-phase systems start at 120/208 volts, go through 277/480 volts, and on into medium and high voltage systems?

What's the matter with a 12/21 volt 3-phase system?

I mean, we already had 120:12 volt single phase transformers. All we had to do was connect the high voltage (120 volt) side of two transformers in series to require the combination be connected to 240 volts, and connect their low voltage (12 volt) sides in parallel, to deliver 10.4 volts when connected to a 208 volt source. Using the 14 volt secondary tap gave us 12.1 volts. Wiring three sets of such assemblies with their composite primaries in delta, and secondaries in Wye (observing such esoterica as instantaneous polarity and equality of interconnecting lead lengths) gave us our three phase system.

We paralleled the whole superassembly to end up with a 3 phase system with a capacity of 1.2kva per phase, and balanced the load so our voltage drop only applied to the one way rather than round trip distance to the center of each branch circuit load. (The #2AWG secondary feeder terminated in a standard circuit breaker panel which had three phase 4 wire branch circuit homeruns via single pole breakers just like a real lighting panel.)

Single Phase 220 Volts and "Single" Phase 208 Volts

Single phase 220 (or 230) volt residential power is generated by a single transformer winding, center tapped to give 110 (or 115) volts between that neutral tap and either end of the winding. "Single" phase 208 volt commercial (and, in urban areas such as Manhattan, residential) power is generated by two of three separate 120 volt transformer windings, connected together at an electrical angle of 120 degrees draw a parallelogram of forces with sides of 120, and you'll ind the resultant to be 208).

The two are not interchangeable. More on this in the next issue.


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