Hi Vyas, I'm not familiar with this standard, but the general principle is that 2 levels of protection are required to protect operators from hazards. In the case of the "protective earthed accessible part", I imagine the standard assumes that a single fault could compromise the protective earthing, so Basic or Supplementary Insulation is also required between such a circuit and SELV. In the same vein, the table requires Double or Reinforced Insulation between an "unearthed accessible part" and SELV.
On Tue, Mar 13, 2018 at 5:56 AM, Balmukund Vyas <balmukund.v...@ymllabs.com> wrote: > > > > > 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 *U*n > = 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 > 6.5.2.4. 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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