Kitchen Unit LED (White) strip/tape lights

[Sponge]

Following on from this thread...

Imagine a kitchen. It's rectangular and has wall and floor units down each of the longer sides. I want under cabinet (shining on worktops) lights on each side. I also want lights on the floor units, shining on the floor.

I have bought 4 x 2.5m LEDs (4 x 36W = 144W) and a 150W driver.

I'd like to be able to run the setup from the one driver. Which would be located on one side of the kitchen, either on top of the wall unit, or under the floor unit. So it would be close to one of the strips and further away from the other 3 (of varying degrees).

I was considering the use of 0.75mm 2 Core Pvc Flex White cable to connect the LEDs in parallel to the driver.

I've read that I need to keep the length of cable to/from each LED strip the same, regardless of distance from driver, to avoid problems.

I was considering wiring all 4 strips to one location, a terminal block of some desription, then wire this to the driver.

Am I way off the mark? Will it work?

 

[RF Lighting]

What is the wattage of each of your LED strips?

How long will the cable runs between the driver and the strips be?

You need to be very careful about volt drop when you're sending ELV over any sort of distance, and even more so with small cable like 0.75mm²

 

[securespark]

I know it's gonna increase your costs, but it'll be less ball busting to get two suitable drivers.

 

[Sponge]

Indeed. You're not the first person to say swap the single 150W driver for two lower W drivers and split the installation into two sections. The 150W driver I bought has gone back, so I am actually in the ideal position to ask them to replace it with two units.

I went for the one driver so I could control all the lights with one on/off switch. If I go with two drivers, there'd be one easily accessible, wall switch for one side and the other would have to be an awkward switch from a wall socket inside a larder unit, which also houses the boiler.

Each LED strip is 36W. (OP edited.)

LEDHut recommended the 0.75mm cable, in an email:

I can confirm that you are able to join 2 separate strips to the same driver. You can connect the strips with 0.75 electrical flex cable (4 core flex for the RGB strip). Any connections made should be done by soldering. Unfortunately we do not supply the cable but you should be able to source this from your local electrical supplier.

Which driver you require depends on the strip which you purchase (wattage) and the total length of strip which you will have. The wattage of each strip (for 2.5m) is shown on the website.

 

[SimonH2]

You would be best to use one driver per location, mounted fairly close to the LEDs. If you can get to run the ELV cable, then you should also be able to run a mains cable and have them operate from the same switch.

BTW - what lengths will you be using ? Rather than think about overall power, those strips are 14.4W/m - so if you use (say) a 2m length then that would be 28.8 (call it 29) W.

While the guy said you can use 0.75mm^2 cable, that does not address length. Yes the cable will carry the current, at least for one strip, but does not address volt drops which could be considerable since the strips take 1.2A/metre, or 12A in total.

In my mates kitchen, pictures posted in the other thread, there are 4 drivers in total - one on top of each cupboard (2x6W & 1x20W) and one underneath for the floor lights (1x36W). He used lower power lights (5W/m) which IMO are perfectly adequate.
The ones lighting the floor have 3 separate supply cables - the longest of which is to the right hand strip and about 3-4m long. I used some speaker cable I had to hand, which when I look it up is about 0.7mm^2 but is only carrying about 12W, or 1A. From your description, it sounds like you could be running 2 to 3 A, over much longer distances and I'd start to worry about volt drops.

Looking in my now out of date BRB*, and extrapolating as the tables only go down to 1mm^2, your 0.75mm^2 cable will drop 58mV/A/m. So say you run one full strip (3A) over 5m, then you'll have 58 * 3 * 5 = 870mV drop. As a rough idea, the LEDs themselves will be dropping around 7V, with 5V dropped by the series resistors. Thus the loss in brightness will be about 0.87/5 * 100 = 17%

* Big Red Book, aka BS7671 17th Edition

 

[Sponge]

One section will have a full, uncut, 2.5m strip under the wall units and probably a ~2.3m length under the base units.

The other section will have a ~2.0m strip and a ~1.8m strip.

LED hut's drivers are priced such that it wouldn't be that much more £ to simply buy another 150W driver and have a bit of head-room. (The 80W driver is very close in price.)

I really hoped to run both sections off one switch and only use one driver (to save ££), but if it can't be done, it can't be done.

 

[SimonH2]

I really hoped to run both sections off one switch and only use one driver (to save ££), but if it can't be done, it can't be done.

You can (regardless of whether you use one driver or more, and you can. The latter is the hardest as you'll need to use larger cable to keep the volt drops down (or accept that some of them won't be full brightness).

BTW - you can join your left over bits together to get one longer bit. You need to completely remove the silicon rubber over the solder pads of one piece, and the adhesive from the underside of the next bit. Then tin (apply solder until it's "taken" to the pads, and then you can lay one over the other and apply the soldering iron to join them. Test after each join - it's easy to make the solder spread and short out between the pads.
Look carefully and you'll find several such joins along each of your rolls.

 

[Chri5]

Just because you have x number of drivers doesn't mean you need more than one switch

Each driver requires a LNE feed, run to / from a junction box (needs to be accessible) or direct to the switch box these feeds can be joined to allow single switch use.

 

[RF Lighting]

Looking in my now out of date BRB*, and extrapolating as the tables only go down to 1mm^2, your 0.75mm^2 cable will drop 58mV/A/m.

Table 4F3B

0.75mm² drops 62mV/A/m, so even worse than your estimate!

 

[Sponge]

When my kitchen was recently rewired, my spark left two cables coming out of the wall on one side of the room (call it the left); one at high level (to cover wall unit LEDs) and one at low level (to cover base unit LEDs). These are coming from a one gang installation box, which I think was to house a switched, fused connection unit. (Spark is coming back during kitchen installation to finish and sign off.)

Could I place one LED driver on top of the wall units and have that supplied by the high-level power cable and feed the upper and lower LEDs on that side, the left, of the room?

Could I then install a 2nd LED driver on the opposite side of the room, the right, but powered by the aforementioned low-level power cable on the left. I would need to extend the power lead (no plug attached) of that LED driver and run it under the floor, in the space below the kitchen?

That way, each side of the room would be controlled by the one switch.

If so, what type of LNE cable is recommended for such a load and environment? A link to something on the TLC website would be useful, as I need to order some stuff from them anyway. I could do with getting the cable put in place as I need to start laying flooring and installing my kitchen units; even if I left the actual connecting up to my electrician.

Thanks for all the input, by the way.

 

[RF Lighting]

Normally, you'd put a driver on top of the cupboard onto the first wire the electrician left, and a second driver onto the bottom wire the electrician left.

You then take a wire from the mains side of the bottom driver to the other side of the kitchen, where it would power a third, and maybe even a fourth driver.

I really can't stress enough how you meed to keep the 12V wiring absoloutley as short as physically possible to get the best performance out of your lights.

As for the type of cable, you'd be best giving your electrician a quick call, and (a) make sure he's happy for you to install this wiring, (b) he's happy to sign off your work as his own (c) what sort and size of cable he wants you to use.

 

[SimonH2]

Table 4F3B

0.75mm² drops 62mV/A/m, so even worse than your estimate!

Ahh, hadn't got that far back, I was looking at 4D2B - I've never claimed to know my way around it that well
For the purposes of the discussion, it's hardly here nor there.

But there's something wrong with the tables. 4D2B gives the volt drop/m/A as 29mV for 1.5, so I doubled that to get 58. 4F4B gives 32. Given that it's specified at a lower conductor temperature (hence lower resistance), the latter should be lower than (or more likely the same as) the former.
And then 0.75 is given the value of 62, which is not twice 32 as it should be.

Ignore stranded vs solid (sizes are given as CSA - so 0.75mm^2 is the same amount of copper either way), and ignore skin effect (the table specifies "d.c. or ...").

 

[JohnW2]

But there's something wrong with the tables. 4D2B gives the volt drop/m/A as 29mV for 1.5, so I doubled that to get 58. 4F4B gives 32. Given that it's specified at a lower conductor temperature (hence lower resistance), the latter should be lower than (or more likely the same as) the former. And then 0.75 is given the value of 62, which is not twice 32 as it should be. Ignore stranded vs solid (sizes are given as CSA - so 0.75mm^2 is the same amount of copper either way), and ignore skin effect (the table specifies "d.c. or ...").

Indeed. There are all sorts of minor inconsistencies both between and within those Tables.

Some of the 'inconsistencies' within Tables can be explained in terms of rounding, rather than 'errors' - but some of the differences (like the 32 vs 62 you mention) are a bit too large to be explained in that way.

I suppose that one (not very satisfactory!) 'explanation' would be that the tabulated figures are actually empirical ones, determined by measurements made separately for each cable size - but that would hardly give one confidence in the measurement procedure concerned!

ISTR that there are one or two actual ('glaring') errors within the Tables but, apart from that, the minor discrepancies/inconsistencies are obviously too small to be of any practical importance.

Kind Regards, John

 

[SimonH2]

... apart from that, the minor discrepancies/inconsistencies are obviously too small to be of any practical importance.

Indeed, it would have to be a very marginal design for the difference between (say) 29 and 32 mV/m/A to be important. Although that is a difference of some 10%

 

[Sponge]

The LED strips will need cutting and wires soldered to the ends without them. The pre-attached wires (3 of them) are 0.5mm 3A, coloured white, brown and yellow iirc.

Looking at my options on TLC Direct, the closest is 0.5mm 3 Core - Pvc White Flexible Cable, but obviously the colouring doesn't match. Or would I be better getting 4-core and disregarding the E?

Is it a big NO-NO to use this cable? To use the earth coloured wire in a non-earthing way?

I also need 2-core cable to run between the PSU and the controller. As the setup is in a kitchen, I was looking at using butyl flexes as 'Can be used in areas where the cable may come into contact with grease or oil.' but they only come in 3-core. Can I use a 3-core and just disregard the 3rd core (E)?