Kaan,
You're correct - that's what the authors of IEC 60950 meant when those words
were added (or so I recall).
Clearance distances are dependant on the peak voltage across the insulation,
even short term peaks (e.g. the assumed 1.5 kV transients on a TNV-1 or
TNV-3 circuit). Creepage distances are dependant on long term voltages. In
Terminal Equipment the ringing voltage is only present for a short time and
so it is (should be) ignored for the determination of creepage distances.
Richard E Hughes
Usual disclaimers apply...
-----Original Message-----
From: [email protected]
[SMTP:[email protected]]
Sent: 13 October 1998 17:50
To: EMC-PSTC
Subject: Re: Crepage/Clearance On Telecom Modem design
Hello,
Its me again, with another two cents (Hey! maybe this one is worth a
nickel... :-).
Clause 2.2.7.4 talks about working voltages for determining Creepage
Distances with no apparent distinction between Primary and/or
Secondary
circuits. The clause lists three bullets, with the third bullet
indicating
that "short-term conditions (e.g. in cadenced ringing signals in TNV
Circuits) shall be disregarded".
This clause seems to indicate that for Creepage Distance
determinations the
ringing voltage is not to be considered as part of the Working
Voltage.
Of course, it could mean something else (these standards can be
pretty
tricky...), does anyone have a clearification?
Kaan L. Gregersen
Regulatory Engineer
3Com
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