Hi Brian:
You describe the problem accurately. The
VDR will start conducting before the required
test voltage is reached.
From a safety point of view, this is not
acceptable unless the equipment is reliably
grounded.
From a functional point of view, this is the
intended performance.
Let's put it this way.
Normal mains voltage is comprised of two
elements:
mains operating voltage;
mains transient voltage.
The safety of the equipment is dependent
upon the mains insulation (between mains
and accessible parts, including ground)
being able to withstand both voltages.
As near as I can discern, surge immunity
is the same as mains transient withstand.
Surge immunity implies withstanding a
1.2x50 impulse waveform, while mains
transient withstand implies a sinewave.
(The mains transient withstand test can
be done with a sinewave, DC, or a 1.2x50
impulse.)
The IEC 62368-1 requirement is that
EVERYTHING connected between mains and
earth must pass a dielectric withstand
test.
Have a Merry Christmas,
Rich
On 12/15/2010 12:33, Brian O'Connell wrote:
> The problem with the VDR being rated for a level 3 surge, which is
significantly greater than the typical test V for BI, is that the VDR will
typically start conducting long before required test voltage is reached.
>
> Di-electric withstand and surge immunity are very different animals.
>
> I saw a VDR from line to chassis in a competitor's component P/S - never
understood the reason for this construction.
>
> Is the VDR rating for 62368 conformity a working voltage or surge rating ?
>
> Brian
>
-
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