volt drop query

[markc17]

Hi all,

Am wiring in some lights in a carpark..
The total distance is 150m
there are 4 lighting posts rated as follows A-200w B-300W C-300W D200W (with A closest to CU)
All loads are LED
They are spread at distances of
CU - A = 30m
A-B = 40m
B-C = 40m
C-D = 40m
Having done my volt drop calcs using 2.5 2c pvc armoured i get a total added Vd of 7.02

Firstly, if anybody can be bothered is this correct?

Secondly,I am aware that the regs state 6.9v as the highest allowed Vd... is there any breathing room with LED loads?

And lastly, if i do have to up my cable size, is it ok for me to use 4.0mm for the first leg of the circuit (CU-A), and then 2.5mm for the rest? This brings total Vd in at 6.

Any help appreciated,

 

[driverman]

It would certainly help with larger cable up front.

 

[telectrix]

for the cost difference, i'd use 6.0mm to A. then 2.5mm from there. have you done your |VD calcs from point to point? i.e --- V @ A, the XXXX V @ B. rtc.

 

[markc17]

yep.. worked out each leg then added them up. Is only so slightly over.. perhaps right.. 6mm for the first 30m bring it in under 6 VD

 

[driverman]

yep.. worked out each leg then added them up. Is only so slightly over.. perhaps right.. 6mm for the first 30m bring it in under 6 VD

You never know...might add in the future, give yourself a fighting chance!

 

[markc17]

agreed...
thanks. Best to use 6 mm at the beginning? or 2 lots of 4mm then 2.5?

 

[telectrix]

don't forget that your OCPD needs to be selected for the |CCC of the smallest cable.

 

[Richard Burns]

Volt drops for each leg with different sizes of cable, totals at the end.

	30m	40m	40m	40m	Total
A	4.348	3.478	2.174	0.870
2.5mm[SUP]2[/SUP]	2.35	2.5	1.57	0.63	7.05
4.0mm[SUP]2[/SUP]	0.95	1.53	0.96	0.38	3.82
6.0mm[SUP]2[/SUP]	0.76	1.02	0.63	0.25	2.66

Just pick and choose to work out which is the easiest and most efficient in terms of cost and cable runs.

 

[D Skelton]

Secondly,I am aware that the regs state 6.9v as the highest allowed Vd... is there any breathing room with LED loads?

Where does it state that then?

And lastly, if i do have to up my cable size, is it ok for me to use 4.0mm for the first leg of the circuit (CU-A), and then 2.5mm for the rest? This brings total Vd in at 6.

What is the voltage tolerace of the LED lighting? Remember you're working to this, not the nominal.

If your LEDs will work between say 200V-250V then you can afford to drop 30V between cutout and last lamp.