Context is a simple, two winding transformer evaluated against the
requirements in the 60950-1 standards. (The following reflects descriptions
of transformers in some test reports I have reviewed.)
Consider:
1) Double Insulation or Reinforced Insulation is required between
windings .
2) A three flanged bobbin that meets the through insulation
requirements for
Reinforced Insulation.
3) Double Insulation consists of Basic Insulation plus Supplementary
Insulation.
4) AWM is used for one of the two windings.
5) A Creepage Distance is provided between primary and secondary
windings
over the center flange that is at least half that otherwise required to meet
Reinforced Insulation.
6) The AWM in 4 is declared to provide Basic Insulation, while the
Creepage
Distance in 5 is declared to provide Supplementary Insulation.
7) 6 is rejected by a safety certifier and the AWM insulation is
forced to
meet Supplementary Insulation. However, because the AWM insulation thickness
is less than 0.4 mm thick, the construction is considered noncompliant.
Similar arbitrary declarations of compliance or noncompliance, are, I'm
certain, a common experience among readers of this list. Other than an
approach that infers that the whim of the safety certifier wins the day, if
their certification is to be applied to a product, what rationale have others
experienced under similar scenarios?
Regards,
Peter L. Tarver, PE
[email protected]
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