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.

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".

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".