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Wiring Matters 93 - Nov 22 - High Protective Conductor Currents

GlasgowMatt

In the latest Wiring Matters issue 93, there is an article on high protective conductor currents and section 543.7.1. 

It quotes the methods of complying with reg 543.7.1.203 including "A single protective conductor, meeting regulations 543.2 (relating to conductor type) and 543.3 (relating to preserving electrical continuity), having csa of not less than 10 mm2 (to give a mechanically robust connection)."

The author then goes on to describe typical circuits and then says this about ring final circuits.

"Where a standard ring final circuit is employed, complying with Appendix 15 of BS 7671 (using typically 2.5 mm2 live conductors and 1.5 mm2 cpcs) it can be appreciated that the total csa of all of the live and protective conductors will easily exceed 10 mm2 – hence satisfying regulation 543.7.1.203."

Do others agree that the authors above interpretation is imcorrect? I dont know where they have got the sum of all live and protective conductors from?

Parents

  • There is a bit about the sum of all the conductors in a multicore cable - between (iii) and (iv) of 543.7.1.203, but as I read it it only applies where you go for the duplicate  ordinary-sized c.p.c.s option (option (iii)) and have both of them in the same multicore cable (protective conductors (plural) are both incorporated in a multicore cable (singular)). Presumably on the basis that it's pretty pointless having duplicate c.p.c.s if the same mishap is likely to break both simultaneously - and that's less likely to happen  with larger more robust cables. I didn't read it as applying when the two c.p.c.s were in separate cables.

    The single ≥10mm² conductor is a completely different option - (i).

    I haven't read the article myself yet - but from what you say it does sound confusing.

       - Andy.

Reply

  • There is a bit about the sum of all the conductors in a multicore cable - between (iii) and (iv) of 543.7.1.203, but as I read it it only applies where you go for the duplicate  ordinary-sized c.p.c.s option (option (iii)) and have both of them in the same multicore cable (protective conductors (plural) are both incorporated in a multicore cable (singular)). Presumably on the basis that it's pretty pointless having duplicate c.p.c.s if the same mishap is likely to break both simultaneously - and that's less likely to happen  with larger more robust cables. I didn't read it as applying when the two c.p.c.s were in separate cables.

    The single ≥10mm² conductor is a completely different option - (i).

    I haven't read the article myself yet - but from what you say it does sound confusing.

       - Andy.

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