Cpc

[entcorp]

Can someone please explain why the site guide / 17th regs requires a CPC of min same size as the PC yet no one manufactures T&E with a CPC the same size.
Even if you double on the T&E up you wont meet the requirement (in & out).

Do we have to wire a separate CPC in a loop (even if you wire radial).?
Or is the use of RCD's negating the need for this ? 543.7.1.4
For example: This is a total pain as there is no way you can fit 2 4mm cpc wires + 2 4mm T&E up a standard 20mm conduit so more hacking at the wall (you'd have trouble with 25mm conduit) or 2 conduit tubes reqd.

Currently studying, HELP ! I am confused here.(site guide 7.6.2,3 )

 

[roukel01]

Onsite guide 7.6.2 is only for circuits having a protective conductor current exceeding 10mA, in which case it must have a high integrity protective conductor connections. But if you read on, ring circuits are fine

 

[Adam W]

You could either run in a separate single core cpc which will need additional mechanical protection unless over a certain csa (4mm² off the top of my head), or wire in singles, or use SWA.
IMO I don't see the problem with using flex, although I'm sure someone else will object....

 

[entcorp]

OK here is a summary:
1) the wiring system on this cb is RADIAL
2) PC on the T&E is 4mm, T&E has 1,5mm earth
3) Sockets are housed in galv gang boxes at 450mm up. Galv 20mm conduit to under floor wiring.
4) for ease of maintenance: no junction boxes under floor, therefore two 4mm T&E go into each gang box.
5) Assume the circuit will have a MCB and RCD as per 17th edition

Questions:
1) Should Galv Conduit be linked to supplimentary 10mm bonding as well as
2) Do I need an addional CPC wire as per site guidefigure 7.6

 

[IQ Electrical]

Take a look at this document, it's worth keeping!

View attachment High Integrity Earthing.PDF

 

[tomxhug]

you need to use the adiabatic equation to work out the acceptable size of CPC you can use conduit but need to check with the manufacture for the equivalent size of conduit as CPC.

The Conduit does need connecting to the MET, This can be done using the metal casing of the DB (As long is it is rated to do so, and you have confirmed continuity and a secure connection between the conduit and the MET.)