On 27/11/2013 10:49, Adam Funk wrote:
On 2013-11-27, John Rumm wrote:

On 26/11/2013 20:49, Bill wrote:
Rumm writes

So, the one technical question that I have. I would imagine that 4mm
singles should be adequate to link the DIN terminals to the RCBOs,
certainly OK for lighting, but should I be thinking of 6mm for some of
the others?

IME RCBOs will come with the required fly lead to connect back to the
neutral bus bar.

They do, I was asking in regard to the tails from the separate DIN
terminals, if I went down that route.

Ah, yes I see what you mean. In that situation then either use the same
or greater CSA as used for the circuit wires you are extending. In the
case of a ring, you ought to either extend both ends, or bring them in
on a thicker single wire which is man enough for the nominal current for
the protective device in question.

So arguably with a ring with a B32 MCB that has two 2.5mm^2 ends, you
would mathematically arrive at 5mm^2 (hence 6mm^2 in practice), however
a 4mm^2 would be acceptable since we know that it can take the full 32A
load.

Does that apply outside the CU too, though? Would it be acceptable to
run a 4 mm^2 cable from a CU up to a junction box upstairs (let's say
it's a good one with Wago lever blocks in it) & then make a ring of
sockets with 2.5 mm^2 starting & ending at the junction box?

Its not a standard circuit as such, although its close to being a trunk
and branch radial in some respects. Its one of those things that you can
demonstrate will work, but at the same time has the potential to cause
confusion later. Its not ideal since you then can't adequately test the
circuit from the CU since you don't have access to both ends.


--
Cheers,

John.

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