Single 2 x 1.5 suitability for dimmer/wall lights.

[ban-all-sheds]

Or, equally, a fused spur from a 2.5mm² ring supplying any number of sockets using 1.5mm²?

 

[JohnW2]

I did consider also mentioning that, but the presence of the fuse would probably mean that some people might try arguing (claiming support from the BS7671 definition) that things downstream of the fuse were not part of the same 'circuit'.

 

[333rocky333]

Im ok with what Bas said but not what John said, i seem to recall we was taught at college that cables should only reduce at a fuse or similar, as you say its not true, but thats what i recall was drummed into us.
I don't recall a time I have needed to do it personally, I have heard of people using 1.5mm and 1.0 for switchdrops to get down existing pipes, I dont like that either, use one or another IMO, also I used to avoid 1mm cable, as said in other posts, companies i worked for forbid it.
Nowadays we do commercial stuff and rarely see 1mm or any T+E, but extreme amounts of 1.5 YY flex.

 

[JohnW2]

Im ok with what Bas said but not what John said,...

Interesting - "What John said" was merely a 'rendition in words' of what is depicted in Fig 15B of Appendix 15 of BS7671 - so is that an aspect of the guidance in BS7671 with which you are "not OK"?

i seem to recall we was taught at college that cables should only reduce at a fuse or similar, as you say its not true, but thats what i recall was drummed into us.

Well, as you know, all that matters to BS7671 is that all cables in the circuit are adequately protected by whatever OPD is protecting them.

Other than the issue of 'intellectual tidiness', I can't really think of any (electrical) problem with a reduction in CSA (as one moves downstream) within a circuit (as above, provided that the lower CSA cable was adequately protected. I could just about see a potential problem (albeit only for the incompetent!) in an increase in CSA within a circuit - since someone finding a downstream 'large CSA' cable might not realise (if they did not work carefully enough) that there was a lower CSA cable upstream (so might, for example, be tempted to up-rate the circuits OPD).

With domestic 6A lighting circuits, it really is irrelevant/moot - since even 1mm² cable represents overkill, and nothing smaller than that is allowed (unless it's flex!).

Kind Regards, John

 

[Draughtsman]

And the capping would either go right around the room at wall light height, or maybe keep the wiring up in the ceiling, just dropping down vertically at each wall light. That room has no ceiling yet, it's just exposed joists.

 

[333rocky333]

I assume you have checked there i s an actual NEUTRAL at your switch, otherwise your plan will not work.