Joe,
I'm away from my data at present. I think IEC 62368-1 in clause 1 states that where a consistent connection to PE/ground cannot be guaranteed, such as with pluggable equipment, protection from mains to the PE requires to be a GDT and varistor to be connected in series.





Regards,

Mick Maytum

Safety and Telecom
Standards

mjmay...@gmail.com

www.ictsp-essays.info


------ Original Message ------
From: "Joe Randolph" <j...@randolph-telecom.com>
To: EMC-PSTC@listserv.ieee.org
Sent: 31/10/2017 02:09:14
Subject: [PSES] Regulatory requirements for MOVs placed line-to-ground on AC mains ports?

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

http://www.randolph-telecom.com



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