cable size for 24vDC confusion

[Andy Wain]

Hi there

I have been following this thread https://groups.google.com/forum/#!topic/loxone-english/OSauABchdwA which has had some interesting discussions about minimum size of cable for 24vDC (it's not the main topic so I started this new one.

it is was this quote from the BS7671 17th edition Regs,

Reg: 715.524.201: The minimum cross-sectional area of the extra-low voltage conductor shall be:

(i) 1.5 mm2 copper, but in the case of flexible cables with a maximum length of 3m a cross-sectional area of 1 mm2 copper may be used.

My question is if this is the case how can the likes of KNX and other control systems manufacture cable for 24vDC which is far less than 1.5mm.

If you have tried to put 1.5mm cable into the 24vDC side of an Loxone nano IO air you will find it does not fit and actually breaks the terminal, making it impossible to use anything over 0.75mm

I wondered if anyone had any light to shed on this confusing topic

Andy

[Kevp]

If you read section 715 then you will see it is applicable to extra low voltage lighting which is what the discussion was about.

For control and signalling 0.5mm2 cable is fine.

Hope this clears up any confusion.

Linky: http://download.hager.com/hagergroup.co.uk/files_download/Ashley_Product_Information/low_lighting_requirements.pdf

[Andy Wain]

Thanks for that.

Where does that leave Loxone tree downlights?

It is lighting, so comes under the remit of that part of bs7671, yet we run tree of knx cable. Not installed tree lights yet.

Would there need to be 2 branches, one for control in knx and one with 1.5mm cable, 4 cores, say 2 twin and earths to each light. Again this would create a pain in the neck with terminating. It would also increase the amount of cable considerably

[Kevp]

I haven't used a tree rgb led yet but from looking at the picture it has 4 cores so I would say you would need to run a single twin and earth for power and a cat 7 for tree control.

On the subject of tree led lights they only make sense up to a maximum of two per circuit after that it works out cheaper to buy a rgbw dimmer for the panel and run a 5 core cable.

I do think they make sense if you want the odd bit of mood lighting in each room, certainly saves space in the panel.

[Peter]

Andy
There's loads of 24v wiring info in this thread:
https://groups.google.com/forum/m/#!topic/loxone-english/oCVZHNdsIL0
Unfortunately none of which refers to Part P regs, hence my renewed confusion.