UK Lighting a Tennis Court

[Greg's Headache]

I want to put 6 300w LED flood lights around a tennis court positioned centre and corners. The cable run is approx. 80 meters. I have a 1.5mm rubber external cable in free air mounted along the top of the mesh fence. 1800w at 240v should give me 7.5a which is within the cable rating but how do i account for voltage losses raising the current draw?

 

[Rockingit]

Eland Cables H07RN-F

 

[timhoward]

Wondering how I got a slightly different R1+R2....!
1.5mm^2 H07RN-F : 32mV/A/m from same page as you = 32 milliohms / m
(80m x 32) / 1000 = 2.56 ohms r1+r2 (both same size) if a radial
R1+R2 for ring = 2.56/4 = 0.64 ohms
Brain not working!

 

[Rockingit]

Wondering how I got a slightly different R1+R2....!
1.5mm^2 H07RN-F : 32mV/A/m from same page as you = 32 milliohms / m
(80m x 32) / 1000 = 2.56 ohms r1+r2 (both same size) if a radial
R1+R2 for ring = 2.56/4 = 0.64 ohms
Brain not working!

We probably both forgot to add the Sunday correction factors.

 

[pc1966]

I would say that while the regs still say 3% for lighting, really for LEDs 5% is adequate, in fact, I suspect that for the same brightness change in LED versus filament lights the old 3% would be closer to 9% now.

But the limit on R1+R2 for something like a 16A C MCB is significant and only likely to be met with a "lollipop" (ring fed from 'radial') and even then it might need 2.5mm for the feed depending on length.

In terms of cables the OP might want to consider NYY-J just because it is likely to stay stiff/straight along the fence route without masses of cable ties, so might look a bit better.

Finally that sort of a load is likely to burn out a 10A light switch fairly soon, I would be inclined to use at least a 20A DP switch instead.

 

[timhoward]

My reflection is that this one really needs someone with a loop tester to advise on the earth loop measurement at the origin before proceeding with the circuit design.
If the OP doesn't have a loop tester (as most diy folk won't) he'll need at least a few minutes of a friendly local sparks time. That may of course reveal the entire place is TT which changes things again.
(BTW I'm in Shropshire so PM me if you want me to take a quick look)

My hunch is that using a 2.5mm ring of H07RN-F is more likely to satisfy the type C breaker's max earth loop as the R1+R2 would be around 0.38 ohms. The NYY-J suggestion is a nice idea and I agree would look neater. (even lower R1+R2 for that too)

 

[pirate]

Can someone explain where the 10A comes from, please...?

 

[westward10]

Can someone explain where the 10A comes from, please...?

I think it runs from Walsall.

 

[Lucien Nunes]

how do i account for voltage losses raising the current draw?

The maximum permissible voltage drop is a small fraction of the supply voltage. We used to say 3% for lighting to maintain the efficiency of filament lamps but with electronic LED drivers that could be relaxed somewhat, as the internal regulation maintains the light output and the efficiency of the fixtures themselves is nearly constant over modest voltage variations. But too high a voltage drop can cause the drivers to malfunction, and it also represents wasted energy (as heat) that appears on the electricity bill. Therefore it makes sense to limit it to say 5-6%, or perhaps 10% at the very worst.

For constant power, the current is inversely proportional to the voltage, so if the absolute worst case is 10% drop, then likewise the absolute worst case is 10% current increase. It's an approximation but there are too many contributing variables involved, including cable temperature, driver efficiency curve, etc, to be worth refining the maths at all.

 

[Rockingit]

Can someone explain where the 10A comes from, please...?

That would be my fault - rounding up 1800W to be 10A for the sake of easier maths in this thread. The real figure would be around 8.7ish

 

[pirate]

Thanks for that! I was assuming that to be the case, but wasn't quite sure!