The Product Safety standards for ITE are generally based on the "single fault"
rule. That is, the device can withstand a single fault and still be safe. If a
Class I
(earth grounded design) device loses its earth ground path, for whatever reason,
internal or external, this is a single fault, and the device is still safe.
A shock hazard can occur only through a second fault, e.g. a failure of the
required
"basic" insulation. This is why it is a safe "practice" to employ Class II
double /
reinforced insulation for Class I designs, as the initial fault (loss of ground)
may be
due to the "house wiring" or other external factor. Using Class II insulation
would
require a third fault, i.e. a failure of the supplemental insulation, for a
shock hazard
to occur.
Applying the principles above, there would be no need to provide parallel or
"secondary" grounding paths.
George Alspaugh
Lexmark
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