Hi Jim:
> 1. Am I correct that the North American agencies (CSA, UL, ETL, etc.)
> allow line-to-ground MOV's? The standards we work with do not
> disallow
> them, but this is the sort of issue for which agencies often invoke
> "desk drawer requirements".
Can't answer this one.
But, why use surge suppressors? What do the suppressors
protect?
If you use line-to-ground suppressors, they are in parallel
with basic insulation and Y capacitors. Both of these will
withstand the normal transient overvoltages up to 1500 V peak.
Virtually all basic insulations will withstand more than 3000
V rms. No problem here.
If you expect transients line-to-ground higher than 1500 V peak,
then use two Y capacitors in series. No suppressor.
The other problem is line-to-line. Again, what do the suppressors
protect? If your input is a switching-mode power supply, then I
suppose the line-to-line suppressor MAY be protecting the X
capacitors and the input diode bridge. Nothing else. The
transients are suppressed by the diode and storage capacitor.
None of the downstream side of the rectifier-capacitor should
see much of a transient.
> 2. Many of you have lots of experience with surge testing for European
> compliance. How common is it (relative to differential mode surges)
> for
> common-mode surges to cause upset or damage? Just as common but it
> takes higher voltages / currents? Less common even at higher levels?
We've not seen any damage to our products due to transients, and
we don't use transient suppressors.
Line transients have been researched and the results published.
IEC 60664 tells you exactly what to expect based on mains voltage
and the sort of installation you are connecting to.
> 3. Does anyone have any real experiences with the supposed shock
> hazard
> that has caused several European agencies to ban line-to-ground MOV's?
My disscussion of this topic was attached to your original
message. As far as I know, they are guessing without testing.
Best regards,
Rich
-------------------------------------------------------------
Richard Nute Product Safety Engineer
Hewlett-Packard Company Product Regulations Group
AiO Division Tel : +1 619 655 3329
Effective 6/12/99: +1 858 655 3329
16399 West Bernardo Drive FAX : +1 619 655 4979
Effective 6/12/99: +1 858 655 4979
San Diego, California 92127 e-mail: [email protected]
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