Hello from San Diego:
Frank McCaughey asks how a generic standard will chose the
approach when multiple approaches exist. He cites the use
of wooden cabinets and plastic cabinets.
As Frank mentions, two or more approaches may be valid.
Safety standards are really of the form:
If .... , then .... .
For example,
If the construction employs a wooden enclosure, then ...
If the construction employs a plastic enclosure, then ...
When the standards are actually written, they don't read this
way. And this is a problem.
Using Frank's example of a wooden enclosure, the standard assumed
that ALL enclosures were wooden. Therefore, no sparks allowed.
Period.
In actuality the standard SHOULD have stated: If sparks are
generated, then enclosure shall not be wooden.
Or: If the enclosure is wooden, then the circuits shall not
produce sparks.
Note that we are talking about protective schemes. The purpose
of the standard is to specify acceptable protective schemes. A
wood enclosure is not an acceptable protective scheme if sparks
can be produced. A plastic enclosure may be an acceptable
protective scheme if sparks are produced, provided other
requirements are met.
Standards should not limit the acceptable constructions, but
should specify ALL the alternative constructions that provide
equivalent protection. Clearly, we don't know ALL constructions,
so the standard must include some sort of test criteria by which
constructions not contemplated by the standard can be evaluated.
Best regards,
Rich
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Richard Nute Quality Department
Hewlett-Packard Company Product Regulations Group
San Diego Division (SDD) Tel : 619 655 3329
16399 West Bernardo Drive FAX : 619 655 4979
San Diego, California 92127 e-mail: [email protected]
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