swa size

[markymark2406]

I want to put a mains supply to my shed, its a 35 metre run from my CU

I just want to have a flouresant fitting within the shed a couple of lights on the outside (1 to be a 300w halagen) and a couple of double gang sockets

Would a 2.5 cable be a good size? and what size mcb should i have at the CU?

 

[Spark123]

2.5 is probably on the small side tbh. What are the sockets to be used for? For a 20A radial you'll probably need 6mm SWA, or if you drop this to a 16A then a 4mm radial will do.
Don't forget this work will be notifiable under part p.

 

[flameport]

2.5mm will only be good for a very small load over that distance, voltage drop will be the limiting factor.

Forget the 300W halogen light as well - not compliant with building regulations.

 

[markymark2406]

well 16 amp radial would be all i need just for use on a hand drill, lawn mower that kind of stuff.

So 4mm it is then what should i put at the CU in my house?

 

[Taylortwocities]

With respect, Marky, you should ask the electrician who is doing the work. Your question leads me to suspect that you don't know enough to do this work yourself (and pass an inspection from the local authority).

It is very basic stuff to know what the value of a protective device should be for a particular sized cable.

 

[markymark2406]

well i have just passed my 17th but cable calculations errrrrr bye.

 

[ricicle]

well i have just passed my 17th but cable calculations errrrrr bye.

And you wonder why we are a frustrated bunch..............

 

[Spark123]

Cable calculations are dead easy - most of it is in the appendix for you. Start with the design current, apply the correction factors and pick a cable from the chart.
Do a quick calculation to see if it complies with volt drop.

 

[ColJack]

or if you've got the internet handy, whack it through this..http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

 

[Spark123]

Be a little bit careful when using the TLC calculator - firstly you'll need to enter the load in watts or kilowatts.
When selecting SWA - select 2 core PVC even if you intend to use 3 core, the PVC limits operating temp to 70deg C.

 

[ColJack]

are you saying the 3 core pvc doesn't?

 

[Spark123]

If you enter 3 core into the TLC calculator it does a 3 phase calculation

 

[ColJack]

you sure?
just did 3 core pvc, 230V, 3KW load...
came back with 13A load..

 

[Spark123]

Did you up your volts to 400?
It always used to do strange things with volt drop and cable sizes unless you enter single phase as 2 core SWA. Maybe they fixed it?

Edit, I don't think they have fixed it - you can see the % volt drop etc change as you go between 2C and 3C SWA

 

[Lectrician]

Cable calculations are dead easy - most of it is in the appendix for you. Start with the design current, apply the correction factors and pick a cable from the chart.
Do a quick calculation to see if it complies with volt drop.

And another to ensure you can offer disconnection with your device and the calculated Zs.

And another to ensure the thermal contraints will be met during a fault.