GreekIslandLover
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Just fried my brain on this one - haven't done calcs since college!
I need to install some exterior lighting in the car park of a small block of flats. Cable to be run from the consumer unit, along the side of the building for half the length of the run, and the other half buried in borders which is mostly tree roots and a little across the driveway that will be paved over. The reason I need to do a proper cable calc is that it's going to be one of my assessment jobs for Elecsa, the other being a consumer unit change I've got lined up. I'm doing the job for a builder mate of mine who is going to do most of the grunt work.
I've been having a look at this based on the information I have, and would like someone to see if I'm in the right direction, or hopelessly wrong! I don't have the BRB to hand - just the brown one. BRB's in the van several miles away.
The length of cable run is going to be about 50M, as I said half clipped outside, half buried. There are four lots of 150W fittings. I've gone with 1.5mm three core SWA for the calculations.
Ib I make to be 2.6A (600w/230v)
In will be a 6A RCBO - not sure if it's type B or C until I know what board it is, and what's available.
It is a little more problematic as I can't find the correct reference method in the brown book for partially buried SWA, so I'm taking the correction factors as 1, leaving me with It = 6A again.
Calculating the volts drop, I used table 4E4B, but unable to use the right reference method. I get (50M * 6A * 27)/1000 which gives me 8.1 v (OK).
Zs I've used copper resistance of 24.2 and over 50m that gives me 1.21 ohms. So either TNS or TNCS will be well within the parameters of a 6a MCB of either type b or c.
So as far as I can see, 1.5mm cable will be OK provided it doesn't go much over 50m, or they don't want me to add extra lights. I do know that they plan to possibly add a couple more lights in the garden (maybe) in the future, so I'm inclined to go with 2.5 to ensure voltage drop and Zs stays ok even if the run is slightly longer and they add a couple more lights.
Am I sort of on the right track with the calculation? Also, how deep should the cable be buried in the borders? It's mostly tree roots, and not cultivated or lawned.
I need to install some exterior lighting in the car park of a small block of flats. Cable to be run from the consumer unit, along the side of the building for half the length of the run, and the other half buried in borders which is mostly tree roots and a little across the driveway that will be paved over. The reason I need to do a proper cable calc is that it's going to be one of my assessment jobs for Elecsa, the other being a consumer unit change I've got lined up. I'm doing the job for a builder mate of mine who is going to do most of the grunt work.
I've been having a look at this based on the information I have, and would like someone to see if I'm in the right direction, or hopelessly wrong! I don't have the BRB to hand - just the brown one. BRB's in the van several miles away.
The length of cable run is going to be about 50M, as I said half clipped outside, half buried. There are four lots of 150W fittings. I've gone with 1.5mm three core SWA for the calculations.
Ib I make to be 2.6A (600w/230v)
In will be a 6A RCBO - not sure if it's type B or C until I know what board it is, and what's available.
It is a little more problematic as I can't find the correct reference method in the brown book for partially buried SWA, so I'm taking the correction factors as 1, leaving me with It = 6A again.
Calculating the volts drop, I used table 4E4B, but unable to use the right reference method. I get (50M * 6A * 27)/1000 which gives me 8.1 v (OK).
Zs I've used copper resistance of 24.2 and over 50m that gives me 1.21 ohms. So either TNS or TNCS will be well within the parameters of a 6a MCB of either type b or c.
So as far as I can see, 1.5mm cable will be OK provided it doesn't go much over 50m, or they don't want me to add extra lights. I do know that they plan to possibly add a couple more lights in the garden (maybe) in the future, so I'm inclined to go with 2.5 to ensure voltage drop and Zs stays ok even if the run is slightly longer and they add a couple more lights.
Am I sort of on the right track with the calculation? Also, how deep should the cable be buried in the borders? It's mostly tree roots, and not cultivated or lawned.
