Thanks for the explanations. However, I still think that at some point
risk assessment is inevitable.
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK
On 2018-04-17 00:22, Richard Nute wrote:
… how do you test *objectively* the adequacy of a symbol like the ! in
a triangle…
The ! is not a safeguard. Ultimately, the safeguard is some
prescribed behavior on the part of a person. The manufacturer of
equipment can only describe the desired behavior. The behavior can
be tested to determine its effectiveness at safeguarding a body.
However, the manufacturer cannot enforce a behavior. Hence, a
behavior safeguard is not necessarily an effective safeguard as is a
physical safeguard.
… requirement for two layers of plastic film or insulation, in case
one layer had a pinhole…
The pinhole was a hypothesis. We totally ignored the fact that the
insulation system is comprised of solid-air-solid (a thin layer of air
separated the two layers). The voltage divides inversely according to
the capacitance. Most of the voltage appears across the thin layer of
air, not the two solid insulations. So, we built in a failure
mechanism to thwart a hypothesis. Fortunately, the system has
sufficent electric strength and the transient voltages at the electric
strength voltage are years apart and of short duration that breakdown
during equipment lifetime is not likely.
Product safety is rife with “conventional wisdom.”
Rich
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