Wiring Matters 93 - Nov 22 - High Protective Conductor Currents

"total csa of all of the live and protective conductors will easily exceed 10 mm^2" 

^{Does not seem like any sensible interpretation to me}

depends if you are considering the tensile strength of the twin and earth compared to single 10mm2 core as the only limiting factor.

However, I think it is a dangerous simplification. In a ring safety comes from the two paths not following the same route and not likely to both be damaged in a way that breaks the CPC but not the live.

The cross section part is a read herring.

In a straight line  pull test I agree the strength is the summed strength of all the cores, but not being pulled around a corner, where one core will see most of the force and fail first, or being flexed repeatedly where the thinner core (CPC) may well not fail at the same time as the others.

I think the authors interpretation of cross sections is 'brave' ;-)

But he is right that a ring is a very good topology for socket circuits where total leakage may be high - just for the wrong reason - it saves the CPC return you would need on a radial.

The spur is a bit of a red herring as you would not put an un-fused commando socket on a spur from the ring - would you?
A 13A socket on any one  spur should not be adding more than 3,5mA of earth leakage.

(to save others the effort of looking the actual article is here

https://electrical.theiet.org/wiring-matters/years/2022/93-november-2022/high-protective-conductor-currents-in-electrical-installations/

)

M.

depends if you are considering the tensile strength of the twin and earth compared to single 10mm2 core as the only limiting factor.

However, I think it is a dangerous simplification. In a ring safety comes from the two paths not following the same route and not likely to both be damaged in a way that breaks the CPC but not the live.

The cross section part is a read herring.

In a straight line  pull test I agree the strength is the summed strength of all the cores, but not being pulled around a corner, where one core will see most of the force and fail first, or being flexed repeatedly where the thinner core (CPC) may well not fail at the same time as the others.

I think the authors interpretation of cross sections is 'brave' ;-)

But he is right that a ring is a very good topology for socket circuits where total leakage may be high - just for the wrong reason - it saves the CPC return you would need on a radial.

The spur is a bit of a red herring as you would not put an un-fused commando socket on a spur from the ring - would you?
A 13A socket on any one  spur should not be adding more than 3,5mA of earth leakage.

(to save others the effort of looking the actual article is here

https://electrical.theiet.org/wiring-matters/years/2022/93-november-2022/high-protective-conductor-currents-in-electrical-installations/

)

M.

I think the author has just got it all confused. As I quoted previously, he says ring circuits with 2.5mm T+E satisfies 543.7.1.203 (presumably (iii)) but it should say it satisfies  543.7.2.201 by virtue of (i) "A ring final circuit with a ring protective conductor. Spurs, if provided, require high integrity protective conductor connections complying with the requirements of Regulation 543.7.1". Although this is implying you need to comply with 543.7.1.203 for the whole circuit

As 543.2.9 requires ring circuits with CPCs not formed from a metal enclosure containing all the ring conductors to be connected as a ring as well, and 543.7.1.204 has been deleted by AMD 2, meaning dual earth terminals in sockets are no longer required, the author is right that almost any ring final circuit wired in T+E will comply as a High-Integrity Earth circuit, just not quite for the reasons they gave