Having had a look at 62368-1 Ed 2, I think the relevant clause in that is 5.5.7. “SPDs” (“Surge Protective Devices”),
5.5.7.1 “Use of an SPD between the mains and earth” “Where a varistor is used between the mains and earth: – the earth connection shall comply with 5.6.7; and – the varistor shall comply with Clause G.8.” Cl 5.6.7 “Reliable Earthing” could be important as that gives familiar “reliable earthing” methods for some equipment. 5.5.7.2 “Use of an SPD connected to reliable earthing” “Where an SPD is used between the mains and protective earth, it shall consist of a varistor and a GDT connected in series, where the following applies: – the varistor shall comply with Clause G.8; – the GDT shall comply with: • the electric strength test of 5.4.9.1 for basic insulation; and • the external clearance and creepage distance requirements of 5.4.2 and 5.4.3 respectively for basic insulation. NOTE 1 Some examples of SPDs are MOVs, varistors and GDTs. A varistor is sometimes referred to as a VDR or a metal oxide varistor (MOV). The above requirements do not apply to SPDs: – intended for attenuating transient voltages from external circuits; and – connected to reliable earth (see 5.5.7.1).” The last bit is interesting because it “seems” to exempt SPDs from needing GDT protection in some circumstances – or am I misreading it? Annex G8 “Varistors” then give detailed requirements & tests for such devices. John E Allen W.London, UK From: Mick Maytum [mailto:mjmay...@gmail.com] Sent: 31 October 2017 10:50 To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Regulatory requirements for MOVs placed line-to-ground on AC mains ports? 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. <https://ci4.googleusercontent.com/proxy/MFofr_tNQCXwgtKy4pOGltrWboeOg0trIAQ09WljehD6kkUvW8SehXbZML9-oMSzaVhU8IEwYspmAGD0dS3oOFpWt2UFmpyfF4ypySLi1XKPXOtDDp7JGfCs0IPXxH2j6mPXQA=s0-d-e1-ft#http://www.ictsp-essays.info/wp-content/uploads/2016/10/ITU-ASSOCIATE-BLUE.png> Regards, Mick Maytum Safety and Telecom Standards <mailto:mjmay...@gmail.com> mjmay...@gmail.com <http://www.ictsp-essays.info> www.ictsp-essays.info ------ Original Message ------ From: "Joe Randolph" < <mailto:j...@randolph-telecom.com> j...@randolph-telecom.com> To: <mailto:EMC-PSTC@listserv.ieee.org> 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) <mailto:j...@randolph-telecom.com> j...@randolph-telecom.com <http://www.randolph-telecom.com> http://www.randolph-telecom.com - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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