gkenyon said:

I think at this point, John Peckham  would be advising us that whatever we decide, we need to be sure that we can justify that when (to completely rip off John's turn of phrase)  'gripping the rail' ?

I am a little surprised that nobody has mentioned Appendix 15.

The plain fact is that either the circuit is a defective ring or it is a radial which branches at the DB. It follows that one way of fixing the circuit would be to reduce the MCB to 20 A (or less). If I did that, I'd also be inclined to isolate the defective cable rather than leaving L and N in situ.

gkenyon said:

Agreed ... we all learn a lot from participating in this Forum. And the statement regards experience was not meant to be directed at you (or anyone else in particular) ... just an important consideration, that no-one ought to be "proclaiming" at us with fixed rules that are immutable for periodic verification.

Absolutely! Interesting turn of phrase…periodic verification. I don’t believe I have seen it referred to in U.K. before although it is what is used in Chapter 6 clause 6.5 in IS10101 2020. I think the regs in Ireland have tighter connections with the HDs.

Might GKs phrasing point to a possible future change in the title of chapter 65? 

It would be a non standard circuit, to have a ring of L and N and a crab claws of earth. No risk of overload at 32A OCP 

Clearly not an immediate death risk in the way of say the socket smashed off and the L and N wires poking out but it would be a brave fellow who said it warranted not even a cursory check.
At least you now need to plug in the Zs meter and verify to all sockets as you have no idea if there is a single break in the ring, or a long dead section and a string of unearthed ones. Of course CPC may be provided by conduit so there may not be an actual wire, but there should be continuity.

By you have done that, you have done 90% of the fault find.

In some southern EU countries you could fit an RCD and then walk off, but not really under UK regs.

Mike

how do Mike

"At least you now need to plug in the Zs meter"

The OP and further on confirms that Zs good at all points  and when considering the question, to suppose that everything is looking reasonable (prot dev, conductor sizes, condition etc) with the circuit (without pulling it apart) other than the cpc is discontinuous (when checked at the board).    Then  consider the OP question.

As commented in this discussion thread, the circuit is not as it should be and there have been other comments  why  it should be condemned to being potentially dangerous  (technically and or  in context of eicr as an unsatisfactory  outcome etc ) as opposed to    needing improvement for safety as such.  Anything can become potentially dangerous of course :-)

There has been differing opinion when similar questions raised previously and it appears that still exists ...  but there is more a lean to the 'dangerous' assessment it seems... 

Regards

On a slight tangent (or thought experiment if you like) - say someone had deliberately installed a long thin circuit with L&N wired as 2.5mm² rings but PE as a 1.5mm² radial (looped into each socket in turn but finishing at the furthest socket) - so much as you might have if done for a ring in steel conduit with the conduit as c.p.c, but with a copper c.p.c. instead.  Zs at the furthest socket within what the OSG says for the required disconnection time given the OPD and a 1.5mm² Cu c.p.c..

Definitely doesn't comply with all BS 7671 requirements, but is there any actual (potential) danger? Would it warrant a C2 on an EICR?

    - Andy.

lyledunn said:

Might GKs phrasing point to a possible future change in the title of chapter 65? 

Not subliminal messaging on my part. Chapter 65 in BS 7671 is titled 'Periodic verification' in the IEC and Harmonized standards.

And to be honest, it was quicker than typing 'periodic inspection and testing'.


NOW ... my pedantic mind should really have told me that 'periodic verification' is, well, wrong, given the definition of verification in BS 7671 ... compare with the purpose of periodic inspection and testing in Regulation 651.1, and you'll see why (at least in BS 7671) it's not correct to say 'periodic verification'. ('Satisfactory for continued service' whereas verification is about 'compliance with BS 7671'.)

Still, people talk about  'Doing an EICR' ... isn't that  'filling out a form' ?

On the subject of a RF with a 1.00mm cpc. I recall back when I did inspections that such a circuit would not comply if it was protected by a BS3036 fuse but would comply if protected by a BS3871 or BS60898 mcb. Since when has this changed?

whjohnson said:

Since when has this changed?

Since then, there have been two changes to the calculation "numbers" which (on paper - separate debate 'real world vs paper') can make the answers different:

(1) Drop from 240 V to 230 V; and

(2) Use of Cmin.

Those would of course give you a lower current at the furthest end of the cable.

In addition, we now look at I²t for certain fault levels with circuit-breakers differently, particularly for highest prospective fault current at the origin of the circuit.

So, Real World, nothing has really changed to make any significant difference.

Paper means needless rewire or derate to 16A.

whjohnson said:

So, Real World, nothing has really changed to make any significant difference.

Not a direct conclusion in my opinion ... as I said, a separate debate.

What if new information came to light, that our calculations to previous editions of BS 7671 did not take into account certain things that happen in  the real world?

I'd agree the move to 230 V from 240 V could be considered questionable in this regard (although move to 230 V we have, and if we are doing calculations based on nominal voltage, things will change by some 4 % for first order proportionality).

But C_min and a change in the way we consider let-through energy of circuit-breakers are, in my opinion, definitely "new information to take into account".