Dear All, IEC 62052-31 is standard for product safety requirements for electricity metering equipment. It has a table 20 (given below) which details out insulation requirements between various types of circuits. My question is, why Basic insulation is required between SELV circuit and protective earthed accessible parts? Isn’t a functional insulation is sufficient for this?
Thanks B M Vyas Table 20 – Insulation requirements between circuits and between circuits and accessible parts HLV mains-circuit1) ELV circuit SELV circuit PELV circuit PEB circuit2) Protective earthed HLV non-mains-circuit2), 3) Unearthed HLV non-mains circuit3) HLV mains-circuit 1) F/B1) 6) Table 8Table 9 B Table 8Table 9 D Table 8Table 9 D Table 8Table 9 B5) Table 8Table 9 B Table 8Table 9 B Table 8Table 9 ELV circuit B Table 8Table 9 F/B6) Table 13Table 14 B Table 13Table 14 B Table 13Table 14 F/B5), 6) Table 13Table 14 B Table 13Table 14 B Table 13Table 14 SELV circuit D Table 8Table 9 B Table 13Table 14 F/B6) Table 13Table 14 F/B8) Table 13Table 14 B Table 13Table 14 D Table 13Table 14 D Table 13Table 14 PELV circuit2) D Table 8Table 9 B Table 13Table 14 F/B8) Table 13Table 14 F/B6) Table 13Table 14 B Table 13Table 14 D Table 13Table 14 D Table 13Table 14 PEB circuit2) B5) Table 8Table 9 F/B5), 6) Table 13Table 14 B Table 13Table 14 B Table 13Table 14 F/B5) Table 13Table 14 B Table 13Table 14 B Table 13Table 14 Protective earthed HLV non-mains circuit2), 3) B Table 8Table 9 B Table 8Table 9 D Table 8Table 9 D Table 8Table 9 B Table 8Table 9 F/B6) Table 8Table 9 B Table 8Table 9 Unearthed HLV non-mains circuit3) B Table 13Table 14 B Table 13Table 14 D Table 13Table 14 D Table 13Table 14 B Table 13Table 14 B Table 13Table 14 F/B6) Table 13Table 14 Protective earthed accessible part2), 7) B Table 8Table 9 F/B6) Table 13Table 14 B Table 13Table 14 B Table 13Table 14 F/B6) Table 13Table 14 B Table 13Table 14 B Table 13Table 14 Unearthed accessible part7) D Table 8Table 9 B Table 13Table 14 B Table 13Table 14 F/B6) Table 13Table 14 B Table 13Table 14 D Table 13Table 14 B/D 4) Table 13Table 14 Abbreviations for insulations: B: Basic insulation or supplementary insulation D: double insulation or reinforced insulation F: Functional insulation S: Supplementary insulation 1) If the functional voltage (not relative to earth/ground) is greater than the rated insulation voltage, the creepage distance for the functional insulation may be greater than that for the basic insulation. An example is a terminal block of a three-phase metering equipment with Un = 230/400 V, where the functional phase-to-phase voltage is 400 V r.m.s. For an indoor meter with material group III, the creepage distance for basic insulation from Table 9 is 3,2 mm, but the creepage distance for functional insulationfrom Table 14 is 4,0 mm. 2) Connections to the protective conductor shall comply with 126.96.36.199. Otherwise, this shall be considered to be an unearthed circuit. 3) There shall be at least basic insulation between HLV non-mains circuits and HLV mains circuits. 4) Insulation between an unearthed non-mains circuit at hazardous voltage and an unearthed accessible conductive part shall satisfy the more onerous of the following: - double/reinforced insulation, the working voltage of which is equal to the hazardous voltage; or - supplementary insulation, the working voltage of which is equal to the voltage between the non-mains circuit athazardous voltage; and · another non-mains circuit at hazardous voltage; or · a mains circuit. 5) See Annex Bfor the conditional use of basic insulation for PEB. 6) Supplementary or basic insulation shall be used if one of the circuits is an independent circuit or is adjacent to a conductive part which may be earthed when the equipment is installed. 7) A functional earthed circuit shall be treated as an unearthed accessible part. The exception is where the functional earth is bonded to the protective conductor and this meets the relevant requirements, then it may be treated as an earthed accessible part. 8) For a PELV system earthed at one end of a cable run, it would be permissible to connect a SELV system at the other end. NOTE Reference is made to the respective tables specifying clearances and creepage distances. This e-mail and any files transmitted with it are for the sole use of the intended recipient(s) and may contain confidential and privileged information. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies and the original message. Any unauthorized review, use, disclosure, dissemination, forwarding, printing or copying of this email or any action taken in reliance on this e-mail is strictly prohibited and may be unlawful. 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