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

I think I agree with you, Andy. The immediate problem with this is that the requirement for "the same wiring system" means that a G/Y with an SWA is NOT the same wiring system, nor is using structural steelwork, or even adding supplementary bonding to meet disconnection times. The fact there is a cross-connection of various Earthing conductors is not in itself dangerous, it is inadequate isolation for work that maybe. This is not the fault of the design, which with multiple connections is actually SAFER, it is the inadequate electrician that is. Whilst isolating a single circuit may be convenient using the single pole breaker, there are many unintended consequent outcomes, the least of which is tripping any common RCDs when N and Earth are accidentally connected. The Neutral is obviously dangerous should another fault occur, as it may well rise to half mains potential. I suggest that working on a circuit requires isolation of all live conductors (which includes the neutral) using the available double pole isolation. This regulation is simply a can of worms that has very little meaning, particularly on larger installations. The next edition will probably add something along the lines "A CPC may only have an electrical connection to a single circuit" which is both daft and impossible!

The idea is to achieve ADS so we're allowed many options for the earthing and bonding. Whether we use containment for multiple circuits or as with bonding,  building structure. I like individual  cpc as it can help with fault finding.

I remember Normcall was happy to pinch an earth when needed to make a safer install for his client.

AJJewsbury said:

I guess it's possible that one T&E can run in the immediate proximity of another T&E (like a G/Y run alongside SWA) - even extraneous-conductive-parts may be used as c.p.c.s (543.2.1 (vii)) -so certainly no requirement to be part of the same wiring system. In any event if there was an upstream RCD all it would take would be a flick of the pen by the designer to nominate that as the ADS device.

Interesting point of view.

So ...

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

Another conductor in the same 'containment' could well be considered the same 'wiring system'.

But, if the cable is run adjacent to other cables, then potentially:

Wiring system. An assembly made up of cable or busbars and parts which secure and, if necessary, enclose the
cable or busbars.

So, cables together are part of the same "wiring system" ... or not?

But if a cable (e.g. insulated current carrying conductors and sheath) can be a "wiring system" on its own, then surely two insulated and sheathed cables on a support system, such as a cable tray, are two separate "wiring systems" sharing the same "support system" ???

Yes Graham, the definition is rather inadequate for the case in point. A C2 is really rather harsh too, it is no more "potentially dangerous" than any other job faced by an electrician, so I would label this one as cash for unnecessary work. These coding books are simply a way out of suitable qualification and experience to carry out EICRs. This one is ideal supporting evidence for my recent paper on the subject!

David Stone said:

A C2 is really rather harsh too, it is no more "potentially dangerous" than any other job faced by an electrician

Just for clarity, I haven't yet supported (or refuted) the coding, just adding to the debate on whether it's "permitted" or "compliant".

"potentially dangerous" - well, I'm not sure either way, and need to think about it further. Under some circumstances, it's definitely "potentially dangerous", and not only to the unwary electrician:

As discussed, where the circuit is disconnected from where the cpc is "borrowed". How could an electrician later on know this, if they are asked to disconnect the circuit with the cpc, leaving the other circuit without a cpc. They are not mind readers, and the circuit without cpc is outside the scope of the work they've been asked to do. The other circuit may even be supplied by a separate distribution board, or from a connection unit of another circuit, so there would be no clue whatsoever.

I can definitely see your point of view, David, but I can also see why some would want to code it C2.

David Stone said:

These coding books are simply a way out of suitable qualification and experience to carry out EICRs. This one is ideal supporting evidence for my recent paper on the subject!

It's great that you are putting some thought into this. It definitely highlights that there are differences in guidance, depending on the opinion of the individuals or organisations who provide guidance on Coding - for example, there are some differences between the ESF BPG and NAPIT Codebreakers.

To play Devil's Advocate, how would one approach a treatise on this subject, which doesn't leave the author(s) of the treatise open to the argument that the treatise is only the opinion of the author(s) on certain coding decisions?

I know that, sometimes, regardless of the industry guidance, there are practitioners in the industry who have their own strong opinions on certain subjects and will code certain things C2 that one or more guidance publications say should be C3, because they don't feel comfortable not highlighting what they see as a serious problem. And in some cases, my sympathies lie with the practitioners rather than the guidance, because they are making the decision and fear they will have to justify it later, potentially as part of an investigation or legal proceedings (civil or otherwise), if something does go wrong.

It's not simply a question of "suitable qualifications and experience".

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.

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!