Hi James,
- Do any other safety standards share this reduction in OVC for PE connected circuits? I'm not completely sure what you mean by the reduction in OVC. This is intended to refer only to the secondary circuit OVC, not the primary circuit OVC. So in the example you gave, the secondary circuit would be classified as OV Cat II, but the primary circuit would still be classified as OV Cat III. This is clearer in IEC 60950-1... With regard to other safety standards, IEC 60950-1 has the same provision (see clause 2.10.3.6), which is likely the source of the requirement in IEC 62368-1. IEC 60065 has something similar but not quite the same in clause 13.3.3. IEC 62109-1 also has a similar concept in clause 7.3.7.1.2c). This one is interesting because it more directly discusses the reduction of OVC across galvanic isolation, with 2 energy sources (photovoltaic input and AC mains connection). If you happen to have this standard, a read through of the whole of clause 7.3.7.1.2 could be helpful. Here's a snippet from 7.3.7.1.2e): *where isolation is provided by means of isolation transformers, optocouplers, or similar* *galvanic isolation devices, between a considered circuit and an adjacent mains or PV* *circuit, the impulse withstand voltage rating of the considered circuit is reduced by one* *level from that of the adjacent circuit; if more than one adjacent circuit is involved, the* *highest resulting impulse withstand voltage rating applies.* On Tue, Jun 15, 2021 at 10:21 AM Joe Randolph <[email protected]> wrote: > Hi James: > > > > I cannot provide a detailed answer to your question, but it appears that > part of the analysis depends on what qualifies as “reliable earthing.” > > > > Most safety standards make a distinction between “reliable earthing” > (typically accompanied by a definition), and what might be called > “unreliable earthing”, which is not a technical term in most standards but > can be interpreted to mean any earthing that does not qualify as “reliable > earthing.” > > > > The basic concept is that an earth connection that was permanently > installed by an electrician is generally considered “reliable,” but the > earth pin on a standard household Type A AC mains plug is generally > considered “unreliable.” These connections are generally considered > “unreliable” because it is known that some household AC mains sockets have > missing ground connections, and it is also known that some users will use a > “cheater adapter” to put a 3-pin grounded plug into a 2-pin ungrounded > outlet. > > > > If the safety protection method used in the product is very dependent on > being connected to a reliable earth, the safety standard typically requires > that the earth connection must be “reliable” as defined elsewhere in the > standard. > > > > Note that different standards have different internal definitions for what > constitutes a “reliable” earthing connection. So, it’s important to use > the internal definition that appears in the standard you are actually using. > > > > > > Joe Randolph > > Telecom Design Consultant > > Randolph Telecom, Inc. > > 781-721-2848 <(781)%20721-2848> (USA) > > [email protected] > > http://www.randolph-telecom.com > > > > *From:* James Pawson (U3C) [mailto:[email protected]] > *Sent:* Tuesday, June 15, 2021 6:53 AM > *To:* [email protected] > *Subject:* [PSES] Overvoltage Categories (OVC) and "Reliable" Earthing - > 62368-1 vs 60601-1 > > > > Hello safety experts, > > > > A question regarding overvoltage categories and “reliable” earthing and > some differences between standards. I would be interested to hear your > thoughts. > > > > *Background:* > > When determining the required withstand voltage for insulation, EN 62368-1 > states that: > > > > *5.4.2.3.3 Determining required withstand voltage* > > *…* > > *If a circuit isolated from the mains is connected to a main protective > earthing terminal* > > *that complies with 5.6.7, the required withstand voltage may be one > overvoltage* > > *category lower** in Table 13 (JP: Table 13 in this case replicates > table F.1 from IEC 60664-1 of OVC vs impulse voltage)* > > > > *5.6.7 Reliable earthing* > > *…* > > *For permanently connected equipment earthing is considered to be reliable* > > *…* > > > > *Summary:* > > A permanently connected piece of equipment with isolated (secondary) > circuit connected to PE is classed as being one OVC lower than it’s > installation eg. OVC III becomes OVC II with all of the reductions in > creepage/clearance/insulation that this results in. > > > > *Problem:* > > - I cannot find an equivalent clause regarding overvoltage categories > and reliable earthing in EN 61010-1. > - Also, I cannot see anything in EN 62368-2 that explains this > decision. > - It looks like EN 62368-1 is a bit of an outlier in this respect. > > > > *Questions:* > > - Have I missed the clause in EN 61010-1 that covers this? (I’ve > looked carefully through Clause 6 and Annex K) > - Do any other safety standards share this reduction in OVC for PE > connected circuits? > - Have I understood the clauses in EN 62368-1 properly? > - I’ve seen (and subsequently unable to find again) a reference that > resistance to transient overvoltages is partly a reliability of equipment > issue. Are the writers of EN 62368-1 less concerned about reliability? ;-) > > > > As always, thanks in advance > > James > > > > > > > > James Pawson > > The EMC Problem Solver > > > > *Unit 3 Compliance Ltd* > > *EMC : Environmental : Safety : CE + UKCA : Consultancy* > > > > www.unit3compliance.co.uk | +44(0)1274 911747 <+44%201274%20911747> | > +44(0)7811 > 139957 <+44%207811%20139957> > > 2 Wellington Business Park, New Lane, Bradford, BD4 8AL > > Registered in England and Wales # 10574298 > > > > > ------------------------------ > > [image: AVG logo] <https://www.avg.com/internet-security> > > This email has been checked for viruses by AVG antivirus software. > www.avg.com <https://www.avg.com/internet-security> > > > > - > ---------------------------------------------------------------- > > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. 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To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
