Ralph, et al,
IEC 62368-1, the Hazard Based Standard, is developed in a way that it
is intended to provide more complete coverage of the hazards encountered from
electrical equipment in its scope and provide more options for manufacturers in
meeting those requirements (albeit this will require looking at the details
more to take advantage of some of the benefits).
In 62368 MOVs are part of the class of Surge Protector Devices (SPDs)
for which requirements are covered in some detail as discussed in this thread.
IN 62368 there are three levels of users for which differing protection
is provided; they are ) ordinary person, an everyday user, perhaps your 8 yr
old daughter, ) instructed person = person instructed or supervised by a
skilled person as to energy sources and who can responsibly use equipment
safeguards and precautionary safeguards with respect those energy sources, and
) skilled person = person with relevant education or experience to enable them
to identify hazards and to take appropriate actions to reduce the risks of
injury to themselves and others.
This differentiation seems reasonable based upon my experience.
Perhaps for TV repair you are not skilled but might be instructed; on
the other hand perhaps you are neither. Where do you fit yourself on this
scale?
:>) br, Pete
Peter E Perkins, PE
Principal Product Safety & Regulatory Affairs Consultant
PO Box 23427
Tigard, ORe 97281-3427
503/452-1201
p.perk...@ieee.org
-----Original Message-----
From: Ralph McDiarmid [mailto:ralph.mcdiar...@schneider-electric.com]
Sent: Wednesday, November 1, 2017 2:38 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Regulatory requirements for MOVs placed line-to-ground on
AC mains ports?
IEC 63386-1 seems to introduce a lot of new terms I have not seen used in other
IEC standards. ( but I haven't read everything out there) I would add that a
"skilled person" perhaps is a "qualified person" , but qualification is often
associated with formal training by an accredited institute, not just on-the-job
experience. I have fixed a few TVs in my time, but I wouldn't say I was
qualified; skilled maybe.
Ralph McDiarmid
Product Compliance
Engineering
Solar Business
Schneider Electric
-----Original Message-----
From: Joe Randolph [mailto:j...@randolph-telecom.com]
Sent: Wednesday, November 01, 2017 12:02 PM
To: Ralph McDiarmid <ralph.mcdiar...@schneider-electric.com>;
EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: [PSES] Regulatory requirements for MOVs placed line-to-ground on
AC mains ports?
The definition of "reliable earthing" appears in clause 5.6.7 of 62368-1, and
it seems reasonable. Equipment that has a permanent earth connection, or
equipment with an industrial "Type B" plug, is considered to have a reliable
earth connection. However, for the ordinary "Type A" plugs used on consumer
equipment such as toasters and computers, the fact that the plug has a ground
pin is not considered, by itself, to provide a reliable earth connection. This
is because users sometimes intentionally defeat these ground connections, and
household outlets are sometimes not properly grounded.
So, clause 5.6.7 contains a complex description of what special circumstances
will allow a Type A plug to be considered a reliable earth connection. An
example would be if the equipment is installed by a "skilled person," such as a
professional installer.
What this leaves us with is that ordinary consumer equipment that has a Type A
plug and is installed b/y the user is *not* considered to provide a reliable
earth connection. Since the earth connection is not considered to be reliable,
a series GDT is required to help protect against excessive touch currents.
I mentioned in my original post that I have seen GDTs placed in series with
MOVs, but did not know why this was being done. Apparently it is being done to
deal with potentially high leakage currents in equipment that does not have a
reliable earth connection.
I still have a question about whether clause 1.5.9.2 in 60950-1 means that
there must be fuses in each of the Line conductors when two MOVs are installed
line-to-ground on the AC mains input. It sure looks that way when I read the
requirement.
Joe Randolph
Telecom Design Consultant
Randolph Telecom, Inc.
781-721-2848 (USA)
j...@randolph-telecom.com
http://www.randolph-telecom.com
-----Original Message-----
From: Ralph McDiarmid [mailto:ralph.mcdiar...@schneider-electric.com]
Sent: Wednesday, November 01, 2017 12:24 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] Regulatory requirements for MOVs placed line-to-ground on AC
mains ports?
The term Reliable Earthing is an interesting one. Does it mean that the
earthing bond is not expected to fail (single fault) and so provides two levels
of protection, as in ‘reinforced” ? I remember arguing this point many years
ago in a product safety review at another company and meeting some considerable
resistance (no pun intended)
Ralph McDiarmid
Product Compliance
Engineering
Solar Business
Schneider Electric
From: Joe Randolph [mailto:j...@randolph-telecom.com]
Sent: Tuesday, October 31, 2017 9:43 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Regulatory requirements for MOVs placed line-to-ground on
AC mains ports?
Thanks everyone for the helpful input. If I am understanding the situation
correctly, it can be loosely summarized as follows:
IEC 60950-1
Clause 1.5.9.2
MOVs connected mains-to-earth or across the mains must have a fuse in series.
The fuse must have “adequate breaking capacity.”
There is no mention of requiring a GDT in series with an MOV.
IEC 62368-1
Clause 5.5.7
MOVs connected mains-to-earth may be connected directly to earth only if that
earth is “reliable” (such as a permanently connected earth).
If the earth connection is not “reliable” (earthing obtained through the
earthing pin of ordinary Pluggable Type A connecter is not considered
“reliable”), MOVs connected mains-to-earth must have a GDT in series,
presumably to protect against excessive leakage current.
Annex G.8
To protect against the risk of fire, MOVs are subjected to a series of tests
designed to overheat them and induce fire. While series fuses are not
explicitly required, the inclusion of a series fuse can be helpful for passing
the tests of G.8
SUMMARY
The above summarizes my current understanding of the requirements regarding
components to be used in series with MOVs when the MOVs are connected to the AC
mains. While IEC 60950-1 requires series fuses, it does not seem to require
series GDTs
IEC 62368-1 requires series GDTs if the earth connection is not “reliable,” and
it’s fire safeguard tests seem to encourage the use of series fuses, although
fuses are not explicitly required in order to pass the tests.
I would appreciate any additional input that might help me determine whether
the above interpretations are correct.
Thanks,
Joe Randolph
Telecom Design Consultant
Randolph Telecom, Inc.
781-721-2848 (USA)
mailto:j...@randolph-telecom.com
http://www.randolph-telecom.com
From: John Allen [mailto:000009cc677f395b-dmarc-requ...@ieee.org]
Sent: Tuesday, October 31, 2017 10:15 AM
To: mailto:EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Regulatory requirements for MOVs placed line-to-ground on
AC mains ports?
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: mailto: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.
Regards,
Mick Maytum
Safety and Telecom
Standards
mailto:mjmay...@gmail.com
http://www.ictsp-essays.info
------ Original Message ------
From: "Joe Randolph" <mailto:j...@randolph-telecom.com>
To: mailto: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
http://www.randolph-telecom.com
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