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Topic Title: SELV LED lighting circuit
Topic Summary: Preferred cable type
Created On: 19 June 2013 08:42 AM
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 19 June 2013 08:42 AM
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davebp

Posts: 106
Joined: 16 April 2009

Hi all,

Thinking about installing some LED dimmers like these:

LED dimmer unit

So, I'd use one 12V LED driver to feed several of these units, which would then feed LED tape / spots in a kitchen, - wiring all plastered in.

Would you use standard twin & earth, keeping the CPC electrically separate from all fittings and the secondary side of the PSU, - this would be cheapest and provide the option of returning the wiring to LV if preferred at some point in the future.

Or would it be better to use a different cable type to identify the wiring as being different from the LV wiring? - Also, as it would be a DC system, is there a requirement to sleeve conductors of whichever cable is used in brown / grey as per table 51?

Thanks,

Dave.
 19 June 2013 08:55 AM
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broadgage

Posts: 1246
Joined: 07 August 2007

I normally use twin flex, do not see the need for anything more elaborate at the low voltages and currents innvolved.

I would avoid any flex or cable with a CPC as this gives more oportunity for future doubt or confusion (to what should it be connected, or if not connected, what to do with it)

Most of the LED drivers that I use come complete with a length of twin flex for the output, suggesting to me that if this is not long enough, that it would be reasonable to extend it with similar material.

Strictly speaking, if blue/brown insulated twin flex is used, then the blue core should be sleeved grey to denote the fact that this is an unearthed or floating system without an earthed neutral.
I must admit though that I dont bother, and have NEVER seen this done.
 19 June 2013 09:44 AM
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normcall

Posts: 8064
Joined: 15 January 2005

I installed a lot of the 24V strips under the wall units in my new kitchen to replace the original florescent tubes.
Made up a board and brought the original supply into a joint box to feed 3 * 36W 24v transformers. Wired 3 supplies down behind the wall cupboards with the transformer end terminating in a J601 (allowed 3 separate 24V supplies), used automotive 2mm twin cable, at cupboard end used a chocbox to change from the 2mm to the 'flying lead' to the strips.
Had to replace all but 2 of the plugs, so not impressed with quality but works well.
One little quirk, the capacitance of the different length cables (and different loads) means each set of strips 'die' at different times when switched off!
By the way, the transformer board is in the loft as I live in a bungalow.

-------------------------
Norman
 19 June 2013 12:32 PM
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dickllewellyn

Posts: 1134
Joined: 19 March 2010

I tend to use twin flex and solder direct to the strips if I can.... Not always possible due to the nature of the job though, so then it's a case of finding somewhere to stash a joint.

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Regards
Richard (Dick)

"Insert words of wisdom and/or witty pun here"
 19 June 2013 12:55 PM
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BigRed

Posts: 552
Joined: 10 November 2006

2 core yy works well, tough sheath, good for teh cable glands too being round in construction. I steer clear of broun blue to avoud confusion with 240 v stuff
 19 June 2013 01:51 PM
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Zs

Posts: 2634
Joined: 20 July 2006

Originally posted by: BigRed

2 core yy works well, tough sheath, good for teh cable glands too being round in construction. I steer clear of broun blue to avoud confusion with 240 v stuff


?

I blame the education system myself

Table 51 on page 116, at the bottom... it's a list of acceptable colours for this circuit. So long you'd be forgiven for thinking Dulux wrote it.

Zs

Edited: 19 June 2013 at 02:01 PM by Zs
 19 June 2013 05:50 PM
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M.Joshi

Posts: 212
Joined: 10 January 2003

Originally posted by: davebp

So, I'd use one 12V LED driver to feed several of these units, ...


Just check first with the manufacturer that multiple dimmers can be connected to the same transformer. Also ensure you choose a transformer that slightly exceeds the power requirement of all the LED lamps/strips together should they want to install higher wattage spots at a later stage.

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M.I.E.T - Forfeited this due to The I.E.T's ridiculous membership rules!
 20 June 2013 01:31 PM
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davebp

Posts: 106
Joined: 16 April 2009

Cheers all,

flex or YY it is then. - 4-core YY if i end up going red green and blue!
Dave.
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