circuits & cables in wiring regs?

[jim]

Still hacking away at my modified ring, another point which needs clarification:

4C1 states:

This is straight out of the original iee regs, but exactly what is meant by 'circuit' and 'cable'?

Taking my modified 2.5mm2 ring as an example, the obvious assumption is that the 2.5mm2 is 'cable' (as opposed to the individual wires within the T&E).

But 'circuit' puzzles me. Is that the whole length of the ring cable from CU back to CU?

The reasoning behind the need for Cg is to allow adequate heat dissipation, so what should Cg be where both ends of the ring run together as they near the CU (several metres in the modified ring as it crosses 2 rooms)? Both ends will be generating heat.

TIA for clarification.

[Tim Watts]

Yes.

That's treated as a single circuits - note grouping does apply to number of circuits, not cables as you noted.

It's pathologically possible to loop a circuit back and forth 50 times and stuff into a confined space so it melts, but so's running a wound up extention lead.

In practice, neither cable is anywhere near full load (or at least not both cables) so it even's out in practise.

The same applies to lighting circuit cables - you could have a real bunch coming out of a juntion box togther on the same circuit but most of them will be carrying next to nothing...

Of course, if you do have a genuine pathological case[1], then you should treat accordingling and not following the regs to the letter.

[1] Eg it is convenient to take a 32A T+E workshop circuit to the edge of the floor (accesibility), into an encosure where it is connected to SWA which for a number of meters runs back right next to the feed T+E, before splitting off. Treat those as 2 circuits for grouping calculations, because, ultimately, physics wins the argument.

Cheers,

Tim

[NT]

everything that runs off the one mcb/fuse/rcbo

NT