Borrowing a cpc from another cct for lighting cct coded C2 in PE magazine codebreakers.

Is another cable classified as 'the same wiring system' ?

Probably not, but why does it matter? 542.6.1 doesn't require it to be in the same wiring system just as long as it's in "immediate proximity" - I'd say two T&Es going though the same holes etc are in immediate proximity to each other in the same was as a G/Y alongside a SWA.

BS 7671 clearly allows shared c.p.c.s or 543.1.2 wouldn't be needed.

Arguments about disconnecting the c.p.c. not realizing it serves another circuit would apply equally to TT systems - where apparently BS 7671 has no requirement about a c.p.c. (shared or otherwise) being routed alongside a different circuit or taking an independent route.

So what potential danger is this C2 referring to?

   - Andy.

AJJewsbury said:

So what potential danger is this C2 referring to?

As I replied to David, I hadn't really gone down that road fully, just the compliance road.

I can see all sides of the argument for C2 vs C3 vs 'no need to code at all'

The Regulation is 543.6.1. not 542.6.1. Anyway, I learn something every day! I reckoned this regulation had more to do with self-inductance should a heavy fault current flow in a separated protective conductor hence no issue with RCD protected circuits.

The Regulation is 543.6.1. not 542.6.1. Anyway, I learn something every day! I reckoned this regulation had more to do with self-inductance should a heavy fault current flow in a separated protective conductor hence no issue with RCD protected circuits.

Yes Lyle, I agree with your analysis. The path of significant Earth current is important in "large" installations, as the potential Voltages on the Earthing system may be very significant, along with very high currents being available. In a domestic I am not worried in the same way, the PSCC is quite low and the danger of damage caused by Earth current is very small, which we know from experience. Whilst there may be some danger from an unintended disconnection of a circuit Earth, surely any competent person would check the Earth loop inpedence of associated circuits, a quick and easy procedure. The immediate clue would be a DB connection without an obvious Earth conductor, probably an old lighting circuit. These always raise a red flag to me, but perhaps not others!