LED strip lighting ---finishing details?

[Alan]

Hi 

Finding the informaiton on here really interesting and daunting at the same time! Lots to learn....and trying to pick up as much as I can before I push the button on a Loxone system. 

Was planning on fitting LED stip lighting for certain areas such as the kitchen and perhaps hidden in the stairway highlighting the treads, (haven't decided what to do for principle lighting yet! seems there lots of pros and cons for that one ;) ) , hiding the nice thin LED strips is not much of an issue, i'm just wondering how people are making the connection between their CAT5/6/7 or power lines and the LED stip itself? I've seen the clips for the ends of the LED stips which are useful but there still has to be a connection to the CAT cable.  I'd like to make it as neat as possible and wonder what tips you'd have? perhaps LED stips directly to a small network point in the wall? a small brush plate? I guess it depends on the circumstances and position but wanted to get an idea for some of the finishing touches with these installs. 

Thanks again for all the great info

Alan

[smartbusinesstools.be]

Alan

Keep in mind that current to LEDs can be high (e.g. 50W / 24V = 2A) so you might need thicker cables.

Soldering would be best, and covering up with a heat shrinking sleeve (or how do you call those in English?)

[Duncan]

it very much depends on the location, detailing of the strip etc

some i solder the short led strip tail directly to the 5 core power lead (dont use cat5/6/7 to power led strip, it takes too much current) and push the soldered joints (with heat shrink insulation) back through the cable exit hole

some i use the specific 5pin led strip plug/sockets where the strip may get disconnected eg kitchen plinths.

[Alan]

Thanks for the replies, thats a good point about being able to disconnect for the plinths and the like. 

I had been wondering about the current also and wasn't sure about using CAT cable for that purpose or long runs in particular , looking at the loxone site their stips draw 86W over the 4 cores, so that just under 1amp per core. What do most people use? 4 core flex or something similar? 0.75mm^2?  3 core and earth? I guess there's a de-rating element depending on where i'm running it also, but i would think some of my runs could be 20m+ back to the unit. 

Thanks

Alan 

[seb303]

I used YY cable for all my LED strips.  Best to calculate what size to use based on the current needed, length of cable run, and acceptable voltage drop / power loss.  Personally I erred on the side of efficiency and have maximum voltage drop of 2%, most strips much less than this.

YY is available in multiple cores, for RGB, RGBW, etc.  When calculating the voltage drop, remember to include both +ve and -ve lengths, and multiply up for common +ve with RGB/RGBW/etc. (i.e. for single colour is lengthx2, for RGB is lengthx4, for RGBW is lengthx5.  Here's the formula:
Voltage drop = 0.0000000172 * <length>/(<cable CSA in mm2>*0.000001) * <current per colour> * 2(or 4 or 5)
Total power loss = <voltage drop> * <current per colour> * <number of colours>

This company does a good range of mounting profiles:
http://www.teucerled.co.uk/
Although you can get more esoteric ones, such as plaster-in profiles.

You can route the cable into the end of the mounting profiles through the little hole in the end cap, or you can drill a hole in the back of the profile and route the cable this way.  Unless you have very short cable runs from the driver, you may find the main cable is too thick to run neatly inside the profile, so you can always join outside and run a thinner wire inside, such as the short length that comes with the LED strips themselves.

There are a lot of options out there, and also for drivers.  I ended up use the eldoLED LINEARdrive series for my LED strips, powered by a few big Meanwell power supplies.  The Loxone turns off each power supply when none of the connected drivers are in use, to save a bit of power.  All drivers are DMX controlled.

One annoyance I've noticed is that sometimes when the power supplies are switched on, there can be a slight flicker in some other lights.  I haven't investigated this fully, but I suspect it may be the switch on spike causing interference with the DMX bus.  I used ordinary cat5 for this on the advice of the guy who supplied my Loxone kit.  In retrospect, a shielded cable may have been better.

[Alan]

Great info, will cetainly make use of it. 

Thanks

[Peter]

Pleased (and a bit relieved) I've just read this thread. I spent ages trying to find out the recommended cable to use for RGBW spots. I wasn't aware of YY cable. I finally asked an electrician who said a Cat 6 cable would be ok. I hadn't really thought much about powering a LED strip, but certainly have now and just in time.
My concern is that I've had duff info from the electrician.
I'm running six Loxone RGBW spots in one room and four WW in another both sets of lights off Cat6. I actually did research the technical details of Cat6 ,AWG, etc. Hope I haven't made a mistake?

[seb303]

Cat6 conductors vary in size from 24 AWG (0.20mm2) up to 22 AWG (0.33mm2).  RGBW needs 4 -ve plus 1 common +ve conductor.  Assuming a single cat6 conductor was used for each -ve plus the remaining 4 conductors for the common +ve, then you have an effective cable run of length x2 over CSA 0.20mm2 to 0.33mm2.

You'd have to do the maths based on actual cable length & CSA to see how much it matters.

The Loxone RGBW spots are quite low power (5W for WW), so if the cable run is short you might get away with it.  There shouldn't be enough power loss to cause the cable to become dangerously hot, but it negates some of the efficiency gains that LED brings, and will also reduce the brightness of the lights slightly.

I certainly wouldn't run any significant length of LED strip from cat6 cable as the power requirements can be much higher than for a Loxone spot.

[Seb]

Im just about to put a wire in to power 4x Loxone RGBW spots. After chatting to Loxone at one of their training days they said that 5core flex (0.75mm2) - same stuff you use for a heating controls should be fine (the run would be about 20m form cabinet to spots). Does anyone think otherwise - I dont quite get the voltage drop mentioned - what drop is permitted before issues are seen?

FYI: Loxone support recommended not to use any Cat 5/6/7 for powering the spots.

[Peter]

Seb, as I've already used Cat6 for my Loxone spots I'm obviously not qualified to offer advice, but if 1.5mm t&e is ok for 240v lighting circuits then I cant see you going wrong with 0.75mm for 24v!

[Duncan]

Peter,
sorry but you cant compare to mains cabling because for low voltage DC lights the voltage is much lower but the current much higher to deliver the same power.
thats why we tend to use high voltage (more dangerous, but much thinner cable required = cheaper)

for rgbw when its fully on, all the current for all 4 channels is flowing back to the common anode through 1 of the wires

at 24v, loxones rgbw dimmer can run 50w or 2.1A per channel, so the single return cable could be running 8.4A

at 20m, the voltage drop at 5% (still quite a lot) would require a 6mm2 conductor area
your lights would be dimmer and the common anode cable has 10w of heating/wasted power being lost in it
cables are usually calculated at 3% generally

the single colour feeds are running 2.1A and 5% loss still requires 1.5mm2 cable at 20m

obviously you may be controlling much less power, and its rare you run for a long time at 100%, but you should calculate accordingly - the 20m is the issue and ideally you would install rgbw dimmers and their power supplies much closer to the leds

for this particular install using 4 spots you have approx 20w across all 4 channels which is 0.83A on the anode
0.75mm2 cable at 20m at 0.83A losses will be around 3% so just about right

[Seb]

Hi Duncan, is there a good site tou can recommend that explains voltage drop, calculations and all that (all new to me and I don't quite get it yet). You have a very good understanding here and I (and probably many others) would like to be able to duplicate and understand it :o)

[Duncan]

there are loads of calculators out there, but this one

http://www.12voltplanet.co.uk/cable-sizing-selection.html gives a reasonable explanation
and
http://www.solar-wind.co.uk/cable-sizing-DC-cables.html is another calculator but isnt accurate for smaller cables/current
http://www.24volt.co.uk/info/Wiring/Wiring

you need some understanding of the circuits and current flow as well, particularly with rgb/rgbw leds because unlike normal circuits, the current isnt the same in all the conductors
http://image.dhgate.com/0x0/f2/albu/g3/M01/23/55/rBVaHVR9_4WAPTuaAAHtmnLCTLw744.jpg

hope that helps

[Peter]

Thanks Duncan, your sage advice is always welcome and much appreciated

[Peter]

Duncan, just to be absolutely sure I've got this right, adjusting your example for 4 spots to six:
Six RGBW Loxone spots generate 5.4w x 6 = 32.4W
So at max power are pulling 1.35A on the anode

Assming a distance of 15m, a 1mm conductor would produce an acceptable 3.7% drop

So the single channel feeds are running 0.34A which using the same distance and a similar 3.7% vd reduces the cross section of the single channel feed conductor to 0.5mm which still exceeds that of a Cat6 cable.

For the return anode I could use two twisted pairs which would handle that current, but I'd still have the problem with the single channels.

Incidentally, probably a stupid question but is the return anode really a max of 1.35A, what about the resistance of the lights?

It seems I'm stuffed and I have to change the wire which of course is buried behind a newly plastered ceiling.

Best I get a new electrician!

[Duncan]

the problem with most electricians is they are used to dealing with 240v lighting circuits and therefore 1.0mm or 1.5mm2 is fine for everything!

yes total anode current is 1.35A/3.7%, and each individual colour cathode will also drop some voltage depending on conductor chosen - if you use 0.5mm2 then each colour channel will drop less than 2% so its not a problem

yes the total current. is 1.35A and leds have an odd non-linear resistance but consume the remaining power delivered to them - but the whole point of avoiding voltage drop in the cable is to try to get the whole 24v to the light so it can consume 5.4w and deliver the maximum lumens - if you lose some voltage in the cable then the bulb will deliver less than maximum light output

there are 2 ways to build constant voltage leds - either the led chips is series with a current limiting resistor, or possibly with a constant current regulator inside - if its an internal resistor then the cable voltage drop will reduce light output, but if its a constant current circuit inside then voltage drop wont have an effect up to a certain amount. but assuming its a cheap and simple current limiting resistor then at 5% its not significant.
http://www.edn.com/design/led/4424539/Overcome-the-challenges-of-driving-parallel-LED-strings illustrates some explanations,
however all we need to know is that at maximum output the cables are rated sufficiently to be at most 5%, but preferrably 3% voltage drop

[seb303]

If you have extra conductors left in your multi-core cable, you can always use multiple conductors for the RGB/RGBW common anode, which will help reduce loss.

I used YY cable for all my lighting wiring, which is available with pretty much any number of cores and conductor size you need.  It's marginally cheaper (although perhaps not so readily available) than using standard mains cable, as you don't pay for the extra copper in the Earth conductor that is not used.

Any competent electrician should be able to do the voltage drop calculations to determine what cable is needed.  But sometimes you may need to remind them that it is low voltage, and hence much higher current.

Seb

[Peter]

Seb.

I have three cores left so I could use four in total to take care of the 1.35A on the anode, however. I'd still have under-rated cables on the other four conductors.

Actually, since this subject got started I've been trying to find more info about wiring 24v lights and as a result am getting my brain completely fried.

When I asked the electrician how to wire the spots, he said loop in, loop out. So what I've got is a cat cable from the driver to the first spot, cat cable from that spot to the next and so on for all six. So a series circuit. My confusion stems from an email I received from Loxone stating they should be wired in parallel. Arghhhhhh

I've found this site which seems very helpful and clearly describes a series circuit for LEDs.

http://www.ledsupply.com/blog/wiring-leds-correctly-series-parallel-circuits-explained/

The bit I'm struggling with here is the description of positive to negative to positive of the LEDs and back to the negative of the driver. I'm taking a bit of a leap here and assuming that the LEDs are handling this flow of current as I certainly don't have a cable from the last LED back to the driver and in any event there's no where to connect it to.

I'm also assuming that the Loxone dimmer is a constant current driver, but I can't find anywhere in the documentation that is stated.

Ok, so back to the problem of the Cat Cable (sorry).

I think I can get away from the cat cable issue if I move the driver from the enclosure to the loft or as close as I can possibly get to the first spot.Therefore the VD will be reduced significantly. I can then run a 24V power cable (suitably rated) to the driver from the enclosure. Unfortunately I'd also have to run the DMX bus to the driver as well. Any ideas how to mount the Driver in the loft? The way I feel right now, I'll just stick a 6 inch nail through it!!!

When determining the distance for the VD, is that the total distance of cable from the driver to just the first spot or from the driver to the first spot added to the distance from the first to the second and so on. In other words the total length of the cable for that circuit?

Hopefully my final question. I'm planning on using the four channels of a Loxone driver to power four rooms of WW spots. The first room is already wired so that's the first channel used but also the only + connection on the driver. So, I use the second channel to drive the next room but where do I get another + from (and then a further two)? Take a feed from the + on the driver  into an inter-connected terminal block and run to each room from there? 

Thanks for the help guys. 

[Peter]

Started clicking on some links on the LEDSupply site and some really useful info

http://www.ledsupply.com/blog/understanding-led-drivers/

[Duncan]

there seems to be some mix-up between the wiring details for bare leds, which are wired in series and driven by a constant current driver (usually 350ma, 700mw or 1050ma)
positive to negative to positive to negative is series, so only applies to bare leds

and constant voltage leds which are connected in parallel, such as the loxone 24v ones

the driver output for each channel is the negative side, and all 4 circuits connect back from the led positive sides back to the common + / anode of the driver

the cable from driver to 1st led will be passing the current for all leds, the cable between 1st and 2nd will pass the total current - current of the first led, 2nd to 3rd will pass the total current - 2 leds etc, so the cable from the driver to 1st led is the most critical to keep short and fat.

for your loxone 4ch driver to power 4 rooms of WW spots, each room will have the driver output going to all the negatives of the spots, and the positives of all leds and all rooms are connected back to the drivers + output, so yes take the + from the driver and connect it to each room via a connector block.

[seb303]

Also to add that: with constant current LED lights/drivers (wired in series), it doesn't increase the current (and hence the needed cable size) when you add more lights.  The limitation in this case is the maximum voltage the driver can provide (which must be at least the needed voltage of each light added together).  Constant current lights are usually more efficient both internally and in the cable size needed - they are however less commonly available.

As Duncan said, with parallel-wired constant voltage LED lights/drivers (as I believe the Loxone RGBW spots are), the more lights you have, the larger the cable size you will need especially for long runs.  Same applies to linear LED strips - the longer the LED strips, the more current needed.  You also have the limitation how much current the strip PCB itself can carry, typically once you get to lengths more than 5m or so.  This can be increased by wiring to both ends of the strip.

Seb (seb303 as opposed to the other Seb!)

[Peter]

Seb303, Duncan

Very helpful replies and I am getting there (honest!). 

Here's me thinking all I had to worry about was programming the beast and I'm down in the weeds of 24V theory which I thought I was leaving to someone else to worry about!

Anyway, two unanswered questions from my previous post, hopefully you can resolve.

If I move the driver from the enclosure to the loft, that solves the under-rated cable / distance problem, correct? All I have to do is ensure the 24V supply cable is correctly rated.I can mount that on a bit of DIN rail.

Incidentally on this subject there are some posts about positioning of drivers / power supplies. Problem being that moving the drivers means running the DMX bus as well.

I'm still struggling with the series / parallel stuff. Would it be correct to state that whilst the spots are wired loop in / loop out (which on the face of it is in series) the wiring inside the Loxone driver would render this method parallel?

At the end of the day the spots I've wired all work. 

[seb303]

Peter, to clarify the series/parallel thing....

Series is like this:
Driver +ve to Light1 +ve
Light1 -ve to Light2 +ve
Light2 -ve to Light3 +ve
Light3 -ve to Driver -ve

Parallel is like this:
Driver +ve to Light1 +ve to Light2 +ve to Light3 +ve
Driver -ve to Light1 -ve to Light2 -ve to Light3 -ve

It's usually preferable to locate the driver fairly near to the lights (thus allowing smaller cable to be used), and then extend the mains power and DMX bus to the driver.

Not quite clear what you mean when you talk about solving the under-rated cable problem.  I don't think it would ever be acceptable to run a number of lights off a single cat6 cable, however short.

[Peter]

Seb303

Ty for the series / parallel explanation. My spots are wired +ve from driver to light1 +ve to light2 as you describe, so parallel (which is a relief)

Re under-rated cable:

Considering Duncan's post and statement that the cable from the driver to the first LED is the most critical, I can move the driver to the loft and reduce the distance from that driver to the first LED to practically zero.

The max current the - channels will be subject to is 0.34A which is within the tolerance of a single Cat6 conductor with negligible VD over a very short distance.

The max current the + channel will be 1.35A for which I will use the four remaining cores of the Cat6 cable.

As you said yourself in an earlier post it's not an ideal situation, but it will work.

Incidentally do people really scatter DMX Drivers all over the house to reduce the need for 'fat' cables?

[seb303]

If you can reduce the distance to practically zero then you'll probably get away with it.  Depending on the distance in between, you might find that some of the lights later in the chain are slightly dimmer.  Can't remember how many you said you have in the chain, but using 4 as an example: the cable from Light1 to Light2 is still carrying 3/4 of the max current.  As you go along the chain, the current is reduced, so the brightness difference between subsequent lights will be reduced too.  If you can't see any difference then I guess you've got away with it :)

Regarding drivers: in my house I have the DMX drivers clustered together per floor, and just run a mains feed + DMX bus to each location.  Much better than having all drivers in 1 central location IMO.  Mind you, it doesn't really avoid the need for fat cables for the more powerful lights.  In one case, I've used 2.5mm cable for relatively short cable run.  This is for a 200W linear LED strip down the length of the ridge beam of the main living area.  The strip is wired to both ends as well.  Mind you, it's a big room with high vaulted ceiling and the light is rarely used at full wack.  Everywhere else I've used 1mm or 1.5mm cable.

Bear in mind also that drivers may need replacing from time to time (more so than the LEDs themselves), so it's a good idea to locate them in accessible places.

[Duncan]

Peter,

the beauty of dmx is it allows that distribution of drivers very easily over a massive area, using rj45 cable and a local power supplies, keeping all dc runs very short. it really doesn't matter how many points you have as a single dmx run can be 500m at least, and a splitter/repeater allows multiple segments and branches if necessary, each up to 500m, all using very cheap parts.

in a typical kitchen install using rgbw strips, you might have a mains supply, 24v psu and dmx driver on top of cabinets, under plinths and under islands - each one will only have a very short run of DC high current, else a single central location in the kitchen say under a plinth with fairly short local DC cable runs.

my kitchen has dmx drivers in 4 locations, the stair handrail rgbw has another location very close by, and i have a third one upstairs and a forth in the garage for rgb garden lighting, but most of my leds are bare leds wired in series using constant current dmx drivers as these are specialised products such as plastered-in wall leds, very small spots with 12 degree beams, or drive-over external leds. i also have 3 locations for mains voltage dmx drivers for my downlights and multiple branches of dmx going out into the garden around all border fences, the drive and multiple flower beds along with 240v feeds so i can add fully controllable lighting outside as and when required using local waterproof dmx drivers.

using 24v downlights requires a degree of advanced planning and knowledge and its unfortunate that most electricians are just not familiar with DC installs.

[Peter]

Thanks Duncan. 

You've mentioned previously employing a lighting specialist for a few hours is a worthwhile expenditure. I think that's probably a good idea!

[Seb]

Thanks for the links for voltage drop Duncan! All makes a lot more sense now. Just swapped my .75 for 1.5 5core (just to be safe).

This thread has a lot of great info in!

[Dick Llewellyn]

Just to throw my hat in and add some points regarding cable size, the way the cable is run will also have an impact. If the cable is covered in thermal insulation as quite often happens in lofts, then the current carrying capacity may well be reduced.

[Peter]

I'll be sorting out my upstairs wiring issues soon. Moving the DMX drivers into the loft with power supplie(s).
Much of this thread has been devoted to VD and minimising cable sizes. I'll probably cluster the drivers together in a central location and provide power from a single PSU. I haven't entirely decided how many 24v lights yet but 4 rooms add up to 11 amps so I guess the other 3 (which includes the landing) will add roughly the same. So to be on the safe side I think I'll need a 25A PSU, any recommendations?
Can anyone suggest a small DIN rail enclosure for about 8 drivers and the PSU?

[Duncan]

i would split the 24v over 2 power psu units eg 2 x 300w - they are cheaper per watt, and give some redundancy so if each room has 2 lighing circuits, each one is driven from a different dmx driver and different psu - that way any failure doesnt back out all lights for a room.

[Peter]

Hi Duncan, thank you for the tip. Any particular PSU manufacturer you'd recommend?

[Peter]

Just to follow up my previous question, There is a huge range of PSUs with a similar price range.

Anybody have experience of this:

https://www.simplypowersupply.com/DIN-Rail-Power-Supply/LP1300D-24MDA-24Vdc-125A-300W-DIN-Rail-Power-Supply.aspx?gclid=CLmR05-5mtECFRITGwodzc8HdQ

[Duncan]

i dont think this will fit in most din cabinets - its very deep
most of the installs ive seen have used the waterproof sealed type screwed to a wall that look like this:

https://www.google.co.uk/search?q=waterproof+power+supply&biw=1239&bih=755&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwiH2IeqrpvRAhUFBBoKHRedCvsQsAQInAE

[seb303]

On Friday, December 30, 2016 at 7:10:49 AM UTC, Duncan wrote:

most of the installs ive seen have used the waterproof sealed type screwed to a wall that look like this:

The Meanwell HLG-320H-24 is a good one, for example.

[Seb]

If you want to stick with the TDKs [1], Future automation have released a deeper cabinet [2] that will take them. I also saw that you can wire some of the TDKs in parallel to have redundancy.

Saying that, I'm def going to checkout Duncan's recommendation.

[1] https://uk.tdk-lambda.com/products/acdc-power-supplies/
[2] http://www.futureautomation.co.uk/Product/Details/LXN-LPS

[RSin]

This is a great thread, exactly what I've been trying to find out.

So am I right in thinking that with RGBW LED strip for example:

19.2W/m x 5m strip = 96W per colour channel (or is it total, so 24W per channel?)

96W / 24v = 4A

so using Duncan's link to ensure <5% voltage drop  http://www.24volt.co.uk/info/Wiring/Wiring

and assuming 5m run, the cable for each colour channel needs to be 0.75mm2

but the return '+' needs to be 4 times this due to the 4 channels = 16A

therefore 2.5mm2

Thanks for all your help guys. 

[Duncan]

the 19.2w is for all channels together - 1/4 per colour

so the common anode has 96/24w = 4A, the 4 colours are 1A each

so 0.75mm per channel or probably less, but 0.75mm for the common anode for 5%

[RSin]

Getting my head around this now finally. Just a bit more detail on cable selection if you wouldn't mind helping.

I can see a few answers above regarding multicore power cable (Duncan) and YY cable (seb303).

How do you justify this with regards to BS7671 to a british electrician?

Have you got links to the cables you found and used?

Is it necessary that these cables are shielded (and all 24v for that matter) or is it more specifically the DMX signal that needs to be shielded?

cheers.

[Duncan]

led DC wiring (and anything else 48v or under) doesnt seem to be an issue under ieee wiring regulations as its deemed inherantly safe, so i dont think youll have any problems with electricians, although this is only the wiring from the 24v psu to dimmers and onto the leds - the wiring to the PSU at 240v will need to be compliant.

some electricans would choose to use 2 x t+e 2.5mm or 4mm for example to feed a dc rgbw circuit and use the 2 earths as the common anode - this is because its familiar, cheap per m and they know it will always meet building regs, particularly if for some reason the DC system is retrifitted with a mains voltage solution later on. the downsides of this is that is more difficult to identify which core is which, its heavy and stiff to work with, and you will still have to use some lighter flex to connect to led strip devices for example

any cable at 240v (or 415 if you are 3-phase) will need to satisfy the electrican that it man meet the latest regulations (along with all connections and appropiate protection/fuse)

low voltage power cables dont need to be shielded, and dmx is supposed to be robust enough not to need it, but based on my own experience then using shielded cat5/6 for both dmx signals and 1-wire can avoid problems and make the system more reliable.

the only thing you really must do with dmx is use a twisted pair for the +/- signals and another strand or the screen/earth for the dmx ground signal.

on a related but different note, one last thing to be wary of is your electrician bunching a large number of 240v cables close together for a long run as they approach your districution cabinet - you can get induction between adjacent circuits particularly if you are dimming, resulting in random and unpredictable tripping of the RCD circuit breakers (ieee mandates every circuit has to be rcd protected) -

electricans tend to use a high current rcd device linked to numerous normal circuit breakers, but this only gives you 30ma leakage for the whole range of circuits fed by that large current rcd breaker - using a non-rcb breaker feeding the same bunch of individual circuits each proteced via a RCBO gives 30ma for each individual circuit and although its costs a little more it can make fault finding significantly easier and less disruptive

[seb303]

You can use either conventional mains cable or YY for your low voltage wiring.  Personally I prefer YY as it comes in any number of cores (useful for RGB, etc.), with each core numbered.  And it is more flexible (stranded rather than solid core).  The CSA can be quite large for high power LV lighting and so solid core cable can get quite unwieldy.

YY also tends to be slightly cheaper as it contains less copper (no unused Earth wire) for the same CSA.  Conventional twin&earth or 3-core&earth are more widely available, but YY is not hard to get either.  I think I got mine from http://www.elandcables.com/

As Duncan said, you'll have no worries from your electrician or BS when wiring for low voltage, although my experience has been that electricians often prefer to use twin&earth or 3-core&earth for LV, simply because that's what they have in stock and are used to using.

I would definitely use shielded cable for the DMX bus, to be on the safe side.  Shielded power cables are not functionally necessary, unless you are aiming for an ultra-low EMR environment for some personal reason - in this case you would want to shield both the mains wiring and the LV DC wiring (PWM dimming produces a fair amount of EMR).  But then you are talking more specialist cabling.

[seb303]

Direct link for YY cable:
http://www.elandcables.com/cables/yy-cable

[RSin]

Cheers guys. I do like the look of the YY cable (and CY for that matter) but according to the BS7671 onsite guide (7.9 Installation and use of non-standard cables) SY, YY, CY are discouraged due to most manufacturers being a bit vague on the compliance and through checking a few datasheets of British manufacturers this would be hard to prove due to use of language like "should" and "mostly" complies. I'll keep digging.

I have found some brands not mentioned, the TKD Kabel came attached to my Roto rooflights so obviously standard on the continent.

Lapp:

https://products.lappgroup.com/online-catalogue/power-and-control-cables/various-applications/pvc-outer-sheath-and-coloured-cores/oelflex-classic-100-cy.html

TKD:

http://www.tkd-kabel.de/index.php?datenblaetter_en

Looks like the best option as you suggest may be the T&E.

Thanks for the DMX twisted pair & shielding and RCBO info, its all these little nuggets that will help build a great stable system.

(FYI chose Roto rooflights as they don't have proprietary control boxes like Velux & Fakro. Links direct to Loxone)

 

[RSin]

Just noticed on your link SEB303 in the datasheet:

"YY control cables are not suitable for fixed wiring applications
requiring compliance with the regulations set out in BS7671" 

[seb303]

I agree that YY cable isn't permitted for 240V wiring under BS7671, even though technically it has a high enough voltage rating.

But the rules for Extra Low Voltage (ELV) supply are different.  This is specifically anything less than 50V AC or 120V ripple free DC.  Note that PWM DC is not ripple free, so think 50V as the limit.  YY cable is fine for ELV wiring.  Check with your electrician if you want a second opinion, but mine was perfectly happy signing it off.

[RSin]

Sorry Seb, don't mean to be a pain, where does it state that ELV rules are different? I just want to understand the traceability through the specs, a bit of a hang-up from working in aerospace! I understand that the cable is capable from an engineering point of view, just the legal side, why can't we just use the same specs as the rest of Europe! From what I can see ELV is part of BS7671, not outside it. I'm think may just go for it and state it in 'Departures from BS7671' on the cert...or just stick with T&E. 

[Duncan]

ELV is part of the specs, in so much as saying which components where have to be (S)ELV such as bathroom fittings etc etc

for things such as low voltage dc lighting it doesnt seem to specify what products you can and cant use

talk to your electrician with the choices of cable - if hes happy to sign of the dc stuff using the cable you are proposing then great, else just run t+e x 2

[seb303]

I'm no expert on the nitty gritty of the wiring regulations, but my understanding is that for low voltage stuff BS7671 does not specify that you must use a particular type of cable - in other words, you can use anything appropriate.

As far as the legal side of things: according to Building Regs Part P you must get the work signed off by a registered electrician.  So I would just direct your question to your electrician.  Mine was perfectly happy with YY cable for ELV wiring.

[seb303]

In fact, I would go so far as to say that ELV wiring is outside of the scope of Building Regs Part P.  So legally you can wire it however you like.  Obviously be sensible and use appropriately robust and sized cable for the application.