Cable sizing for 24V LED lighting

[jjnr78]

I believe I have been wrongly advised by my supplier about sizing cable for a lighting installation and I was hoping that someone with more experience of DC cabling will be able to set me straight.

We are looking to install some LED strips to a coffered ceiling above a swimming pool.
I have specified 24V as the length is 15.5m (x2) by 4m (x2) and the strip is 5W per metre
We are going to treat each length seperately; 2 x 15.5 and 2 x 4m with their own power supplies
However, I dont want to take the 230V into the pool ceiling area and so I've wired 1.5/1.0 twin + cpc from the power supplies to the end of the strip. This length could be 30m as there are only 2 accessible points around the pool. In doing a quick calc its showing that I might need a 10mm cable??? Is this correct?
If this is so, I will have to take the power supplies into the pool area, but there are maintenance issues as well as being cautious with 230V above a pool
Thanks

 

[Landril]

Is the 30M length for DC or AC power and could you show the calc of how you came to 10mm cable to run the 24v 5w strip LED's seems a bit crazy.

 

[Landril]

If i have read this correctly:

15.5.m x 2 = 31m
31m x 5watts pm = 155w
4m x 5watts pm = 20w
2 x (4m x 5watts pm = 20w) = 40w


40w + 155w = 195w if this is how i understand it why would 10mm cable be required mate?

 

[telectrix]

take 1 LED strip at 15.5m, 5watts /m. that's 77.5watts, which equates to 3.23A @ 24V. 1.5mm cable will handle that with ease. VD is 29mV/A/m.

 

[jjnr78]

I used this: DC cable sizing calculator - Energy Matters

Also remember i'm running them out independantly, so its actually 77.5W per 15.5 metre length for example.

Everything I wrote out is the DC wiring. Not that it matters, but i'm connecting the power supplies to a Lutron Grafik Eye in an adjacent room. If it turns out the 1.5 cable is too lean then perhaps i'll take the power supplies (AC) within 100mm of the strips each time.
Thanks

 

[mungo2007]

For this type of install the 24 volt is the right strip to use. I would advise using a 1.5mm twin core cable to run from the transformer to the strip, the strip probably won't take the 1.5mm soldered onto it to just connect to the standard cable tails supplied on the strip, doing it this way you should not experience a voltage drop.

One other point on the 15.5metre section, you may want to feed power at both ends just to eliminate any chance of voltage drops on this longer length.

 

[jjnr78]

take 1 LED strip at 15.5m, 5watts /m. that's 77.5watts, which equates to 3.23A @ 24V. 1.5mm cable will handle that with ease. VD is 29mV/A/m.

Thank you! i forgot a key point, butn i think it makes it better actually, we are using LSF cable. Is that therefore table 4E2B? I didnt know if we could use these tables for DC

 

[jjnr78]

One other point on the 15.5metre section, you may want to feed power at both ends just to eliminate any chance of voltage drops on this longer length.

Yeah i did consider the colour fall off over the length, but I wont be able to maintain the other end should there be a failure. Instead I as going to lay out the strips so they the all start and finish at the same point. I might have to play with that on site. thanks for the heads up

 

[mungo2007]

I that case could you run 2 lengths for the 15.5 mtr cut it in half and then run 2 shorter separate lengths they can both feed from the same incoming 1.5mm supply?

 

[Landril]

I see now you mean DC so 1.5mm will handle the 3.2A d.c. easily on each strip, good thinking on questioning the 10mm cable btw

 

[jjnr78]

I that case could you run 2 lengths for the 15.5 mtr cut it in half and then run 2 shorter separate lengths they can both feed from the same incoming 1.5mm supply?

In theory yes, but it would mean connecting to the strip at a corner i wont be able to get to once the pool is filled.

 

[jjnr78]

I see now you mean DC so 1.5mm will handle the 3.2A d.c. easily on each strip, good thinking on questioning the 10mm cable btw

could've gotten expensive and god knows how i would've connected 10mm to 0.5mm?!

 

[telectrix]

10mm cable, you could turn a wagon engine over. christ,

 

[keniff]

take 1 LED strip at 15.5m, 5watts /m. that's 77.5watts, which equates to 3.23A @ 24V. 1.5mm cable will handle that with ease. VD is 29mV/A/m.

What's the max vd drop on the dc side tel?

 

[telectrix]

15.5m x 3.23A x 0.029 = 1.45V if i've got it right.

 

[keniff]

Sorry mate I mean what's the max vd your allowed on the 24v side

 

[telectrix]

i would imagine 3% for lighting, but all depends on the min. voltage the LED strip requires to be at full brightness.