Hi Chengwee Lai:
> 2. Earth Continuity or ground bond testing with 25A or higher is not
> applicable with plastic case and not applicable at the DC output side. It
> was meant to check the earth protection continuity of a metal chassis.
Protective earthing is required for any conductive
part that is susceptible of becoming live in the
event of a fault. The fault is that of basic
insulation.
At the mains appliance coupler, the insulation
between the mains and the PE terminal is basic
insulation. Depending on the individual unit
construction, there may be other points within the
unit that comprise basic insulation between the
mains and the PE terminal.
If the dc output is connected to the PE terminal,
then the dc output could become live in the event
of a fault in the basic insulation between mains
and the PE terminal.
If the adapter is sealed, then the only way to
test for earth continuity is to check from the
dc output side to the appliance coupler earth
terminal.
> 3. I believe you will have to use 3000Vac or 4242Vdc between primary and
> secondary side, unless you have a failure, then there are steps to go
> through to isolate the failure.
The adapter has basic insulation between mains
and the PE terminal, and reinforced insulation
between mains and the dc output.
If 3000 V rms is applied between mains and the
dc output (which is grounded), then 3000 V rms is
also applied between mains and the PE terminal.
This may lead to early failure of the basic
insulation.
For this reason, Class I equipment is subject to
only 1500 V rms hi-pot.
(If care is taken in the design such that the
basic insulation has an electric strength
exceeding 3000 V rms, then the 3000-V test can
be applied.)
Best regards,
Rich
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