Letters

Get Up, Stand Up In your Editor's Viewpoint, "A Call to Action" (CSE 11/03 p. 7), you noted that in the past, some readers have made it known that you should keep "politics out of engineering discussions." I disagree—it's what makes the discussion more interesting and relevant. To put it in further context, consider this quote I ran across recently from Martin Luther King, Jr: "Our lives...

02/01/2004


Get Up, Stand Up

In your Editor's Viewpoint, "A Call to Action" ( CSE 11/03 p. 7 ), you noted that in the past, some readers have made it known that you should keep "politics out of engineering discussions." I disagree—it's what makes the discussion more interesting and relevant. To put it in further context, consider this quote I ran across recently from Martin Luther King, Jr: "Our lives begin to end the day we become silent about things that matter."

DAVE TROUP, HOK, SAN FRANCISCO

NFPA Not Threatening Litigation in California

We wish to refute a statement implied by Kurt Cooknick, director of regulation and practice for the California Chapter of the American Institute of Architects, in the "Is NFPA 5000 in California to Stay?" installment of the Codes & Standards ( CSE 12/03 p. 21 ). At no time during California's code-selection process did anyone representing NFPA make any statement about potential litigation. Since the July 2003 vote during which NFPA's codes were selected, we have been working with the relevant state agencies to tailor our model building code to the needs of California.

KEN FIELDS, NFPA SPOKESPERSON

Molded Case Switches

In the Technology in Action story "Breaker Discrimination in the Computer Room" ( CSE 11/03 p. 60 ), the author states that non-automatic switches are really automatic. The truth is that standard molded case switches are not automatic. Molded case switches that have tripping characteristics are called, not surprisingly, automatic molded case switches—Where does the author get his terms? Certainly not from a Square D catalog!

This article should have used the term "selectivity" instead of discrimination. Also, the reference to a panelboard as a "remote power panel" by computer room personnel is not an improvement in terminology or an advancement in linguistics of any kind.

Finally, when comparing fused panelboards to circuit breaker panelboards, the author should have used the adjective "physical" in front of the word "size." I know of fused switchboards, but if there are any fused panelboards, I would like to know who makes them.

JOHN K. CARTER, P.E., CAMARILLO, CALIF.

Author Mark Welte, P.E., EYP Mission Critical, responds:

Molded case switches that meet UL 489 must self-protect under high current conditions and therefore contain fixed instantaneous trip elements, typically set at 10X handle rating, and will engage and trip these switches. You must read beyond the marketing or sales information you get from the over-the-counter sales catalogs.

Office Lighting Questions

In the Product Comparison on office lighting fixtures ( CSE 12/03 p. 59 ) you compare various styles of fixtures with categories including "Luminaire Efficiency Rating" (LER) and "watts per sq. ft." By these classifications the noted fixtures produce 40-50 footcandles (fc) on the work surface. However, I don't understand how fixtures of vastly differing luminaire efficacy ratings—74% and 47%, to pick two—can produce the rated light level at the work surface while consuming identical watts per sq. ft. (1.14).

Should we not expect that a fixture with a lower efficacy would require more watts to produce the same light level on the work surface? Does not efficacy relate light output to power input? Please advise.

CARL MEZOFF, P.E.

Author Ingrid McMasters responds:

The fixture LERs for all three types of recessed fixtures should have been shown as a range rather than a specific number. The LER for the particular calculations used were as follows:

Recessed prismatic: 74

Recessed parabolic: 59

Recessed indirect: 55

Using these particular fixtures, I was able to achieve acceptable lighting levels: 40-50 fc on the workplane, with all three fixture types using the same layout (watts per sq. ft).

The formula for LER is luminaire efficiency (EFF) times total rated lamp lumens (TLL) times ballast factor (BF) divided by luminaire watts input (LWI). The goal of this rating is to help the lighting industry establish a "cost of light" which is effective when comparing fixtures of similar design (i.e. indirect to indirect or prismatic to prismatic). It is a voluntary rating which manufacturers can include in their published luminaire data.

Luminaire efficacy ratings vary among manufacturers' designs and can vary due to differing data input such as total rated lamp lumens and ballast factor. For example, one manufacturer I looked at used 2,950 lumens per lamp for their prismatic, 2,900 lumens per lamp for their parabolic and 2,800 lumens per lamp for their recessed indirect. Another manufacturer used 2,850 across the board for all of their T8 fixtures. This can account for slight variations in calculated illuminance levels, but I have found that there is not as much difference in the results of the final illuminance levels than may be construed from looking at the raw LER.

The actual ranges for LER should be something like this:

Recessed prismatic: 67-74

Recessed parabolic: 59-62

Recessed indirect: 42-57

I calculated 52.5 footcandles with the recessed prismatic scenario. Using a ratio to verify accuracy of the recessed parabolic scheme: 52.5 fc x (71/87.5) = 42.6 fc. Using photometric software, 44.81 fc was achieved. Using the same ratio for the recessed indirect scenario: 52.5 fc x (65/87.5) = 39 fc, and with the photometric software 41.4 fc was achieved. Furthermore, the results indicated the calculated footcandle level on a workplane does not seem to have a solid linear relationship to the fixture LER. This may be accounted for by the fact that I inserted 5-ft.-high cubicles in the space.

No Excuses for Buildings with No Sprinklers

Once again life-comfort takes precedence over life-safety. Your article "All Rise" ( CSE 12/03 p. 46) notes that the Ellis County Courthouse [in Waxahachie, Texas] was constructed [in 1895] when there were no air-conditioning or life-safety systems, such as sprinklers.

But in its renovation, for which you awarded the project an ARC Award , the writer, in specifically pointing out preservation efforts, noted how ways were found to conceal and route ducts; that electrical conduits were concealed into walls and ceilings requiring cutting and patching; and that solutions were found to deal with the challenges of locating unsightly HVAC equipment.

Furthermore, in addressing fire protection measures, to note that sprinklers were not an option for aesthetic reasons and that it would have called for more cutting and patching, which would have resulted in an undesirable task, seems to me to disregard exemplary life-safety features of a properly designed and installed fire sprinkler system, instead emphasizing life-comfort systems.

"In lieu of sprinklers" or "an alternate to sprinklers," however, do not present good scenarios in light of recent fire and loss of life publicized occurrences. Having been involved in the fire-protection industry for the last 45 years, I understand that cost was likely a major factor. However, the acceptance of omitting sprinklers due to aesthetic conditions is still disturbing.

DONALD H. TESKE, GLOBAL FIRE PROTECTION CO., DOWNERS GROVE, ILL.





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