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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?

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  • It appears to me that 543.7.1.202 and .203 contradict one another. .203 requires a 10mm conductor although installed whereas flexible cables to a plug may be 4mm2.

    I don't read it like that - .203 only demands a 10mm² if it's exposed - permitting 4mm² if enclosed (it gives the example of flexible conduit, but a flex sheath where it is suitable for the environment will likely give similar protection). .202 aligns with that pretty well - other than it permits  a reduction to 2.5mm²  for 16A plugs - presumably just driven by the practical limitations of getting 4mm²  into a 16A terminal.

       - Andy.

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  • It appears to me that 543.7.1.202 and .203 contradict one another. .203 requires a 10mm conductor although installed whereas flexible cables to a plug may be 4mm2.

    I don't read it like that - .203 only demands a 10mm² if it's exposed - permitting 4mm² if enclosed (it gives the example of flexible conduit, but a flex sheath where it is suitable for the environment will likely give similar protection). .202 aligns with that pretty well - other than it permits  a reduction to 2.5mm²  for 16A plugs - presumably just driven by the practical limitations of getting 4mm²  into a 16A terminal.

       - Andy.

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