Alan,
You stated that:
>Paragraph 5 of clause 6.4 of EN60950/A4 which follows items a) b)
>and c) states the following:
>
>'These requirements do not apply where circuit analysis and
>equipment investigation indicate that safety is provided by
>other means, for example between two circuits each of which
>has a permanent connection to earth.'
Your reference to 6.4 above should actually be 6.4.1 which specifically refers
to electrical separation (see also Table 19), not the impulse test of 6.4.2.1.
However, if a TNV-1 or TNV-3 circuit and an SELV circuit are permanently
connected to earth, then there may be no separation requirements between them,
therefore, no testing should be required, if I'm reading the standard
correctly.
If an overvoltage fault occurred (such as an impulse of 6.4.2.1 that you
mentioned) between unearthed TNV-1 or TNV-3 circuits or conductive parts and
an
SELV circuit (in this case), that fault current must be reliably routed to
earth (see 2.3.3.3). In particular, the "permanence" of the SELV connection to
earth is described in 2.5.11, particularly the 2nd to last paragraph. See also
6.3.2.
I hope this answers your questions and that you will be soon out of your
misery. :-)
Comments anyone?
Best regards,
Ron Pickard
[email protected]
