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 (USA) <mailto:[email protected]> [email protected] <http://www.randolph-telecom.com> 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 <http://www.unit3compliance.co.uk/> | +44(0)1274 911747 | +44(0)7811 139957 2 Wellington Business Park, New Lane, Bradford, BD4 8AL Registered in England and Wales # 10574298 _____ <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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