Hi Scott:
Class II products have two levels of insulation: basic and
supplementary insulations. Each insulation is safe to prevent
from electrical shock in normal use. Why does a product need two
levels of insulation in its lifespan? How often is a second
insulation being used?
Basic insulation is a safeguard against electric shock under normal
conditions.
Supplemental insulation is a safeguard against electric shock under
fault of basic insulation.
Basic and supplemental insulations are chosen that what deteriorates one
will not deteriorate the other.
The probability of failure of two insulations is multiplication of two
very small probabilities which is a very very small probability.
Today's insulations are very good and not likely to fail throughout the
lifetime of the equipment. This wasn't always the case.
Nine out ten people do not know the meaning of class II symbol.
What is main purpose to have a double square symbol on class II
products?
The double square symbol means class II as opposed to class 0 (which is
two-wire without double insulation).Only design
and test people need to know the meaning of the class II symbol.
Hope this helps.
Rich
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