Hello Chengwee:
> Whether customer can accept his adaptor with only 1500Vac hipot tested
where
> other power supplies can withstand 3000Vac?
This is an interesting question as it implies
that the higher the withstand voltage the better
the unit. The statement may even imply that a
double-insulation scheme provides a better
safeguard against electric shock than does a PE
scheme.
In fact, the two schemes provide equal protection
against electric shock. There is no *inherent*
advantage of one over the other.
The 1500-volt withstand value is derived from
the normally-occuring mains-to-earth overvoltages
plus margin. In other words, the 1500-volt test
represents an acceptable insulation that will not
fail when subjected to mains-to-earth overvoltage.
The 3000-volt withstand value is derived from
testing two 1500-volt insulations in series. The
3000-volt test tells us that the two insulations,
as a system, are acceptable, assuming that the
voltage divides equally across each insulation.
(The two insulations will never see overvoltages
as high as 1500 volts.)
There is no inherent advantage to a unit that
passes a 3000-volt withstand test versus a unit
that passes a 1500-volt withstand test. The only
thing that the 3000-volt withstand test tells us
is that the double-insulation system is intact.
If I recall correctly, Raymond Li said that the
unit in question passes 3000 volts primary-to-
secondary, fails 3000 volts primary-to-earth,
but passes 1500-volts primary-to-earth.
This tells us that both the basic insulation and
the double insulation are acceptable.
> Would that affect his customer Safety testing, because his customer unit
> with his power supply only meet 1500Vac hipot after heating test?
If the customer wants double-insulation throughout
the unit, then the adapter is unacceptable.
If the customer wants a unit that is certified to
a safety standard, then the adapter is acceptable.
> Or what if Safety agency require his customer unit to do grounding test to
> accessible metal part?
Based on Raymond Li's description and on my own
experience, I believe there should be no problem
passing the production-line grounding test at
25-amperes.
*****
Despite the preceding comments, such an adapter
should easily pass double-insulation requirements
between primary and ground, and between primary
and secondary. In my experience, adapters designed
to IEC 60950 can easily achieve more than 4500 V
rms withstand. And, they can easily achieve 25
amperes dc-to-PE.
So, I am a bit disturbed that the unit does not
pass 3000 V rms to earth. This says to me that
there is a clearance within the unit that does not
meet the IEC 60950 requirements. I would further
guess that the clearance is likely to be an
operator-dependent clearance that is determined
during the assembly of the unit. (The IEC 60950
clearance dimensions are quite conservative, and
should not break down below about 5000 V rms.)
Best regards,
Rich
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