Hi Joe,

IEC60950, clause 1.5.9.2 requires - for the protection of the VDR - "an 
interrupting means having an adequate breaking capacity shall be connected in 
series with
the VDR"

Best regards
Kris Carpentier,

From: Joe Randolph [mailto:j...@randolph-telecom.com]
Sent: dinsdag 31 oktober 2017 3:09
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] Regulatory requirements for MOVs placed line-to-ground on AC 
mains ports?

** WARNING: This mail is from an external source **

Hello All:

Aside from surge tolerance during normal type testing, are there any regulatory 
requirements regarding the placement of MOVs from line to ground on an AC mains 
input port?

I seem to recall that some countries or standards are concerned about potential 
hazards associated with MOVs developing high leakage current, over time, in 
response to repeated surge events.  I've seen circuits where a GDT was added in 
series with the MOV, and I believe this had something to do with concerns about 
MOV leakage current.

I've also seen MOVs offered for sale that are packaged in a way that physically 
couples them to a thermally-activated one-time fuse.  This implies a concern 
with the MOV becoming leaky over time and overheating.

While I am familiar with the potential failure mechanism of MOVs developing 
high leakage current over time, I cannot point to any published safety standard 
that imposes any construction requirements that attempt to protect against this 
failure mode.  I thought I remembered seeing something on this topic many years 
ago in a UK standard, but that was a long time ago, prior to harmonization of 
the IEC 60950 series.


Thanks,

Joe Randolph
Telecom Design Consultant
Randolph Telecom, Inc.
781-721-2848 (USA)
j...@randolph-telecom.com<mailto:j...@randolph-telecom.com>
http://www.randolph-telecom.com

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