Electric cable size for outside shed

[djhope]

Hi,
i'm fitting power to my shed at the bottom of the garden which is 40m away. What size cable will I need to use would 2.5mm twin + earth be ok or will I need to use 6mm?
I will need to run lighting, radio, one power tool at a time. etc.

2.5mm cable would be great as it will be easier to fit and is cheaper.

your help would be great

Thank you

 

[plugwash]

A 20A circuit is the minimum I would use for an outbuilding supply. Volt drop is the dominating factor at this distance and unfortunately means that even for a 20A circuit you need 6mm.

 

[Qedelec]

There is more to choosing what size cable than an estimate of what you are going to use on it. You need to take into account what current you need, how long the cable is to be, method of installation, volt drop and thats just for starters. The cable needs to be mechanically protected so Steel Wired Armoured is favourite, oh and just to inform you, this work is notifiable to LABC and all circuits to your shed will need RCD protection. Sorry to be pedantic.

 

[djhope]

Thanks for your prompt replies.

Happy Easter

David

 

[kwikfix328]

and all circuits to your shed will need RCD protection. .

I can see that all circuits inside the shed would need to be RCD protected, can you just confirm that the actual supply to the shed has to be RCD protected too ?

If the shed has a 30ma trip RCD consumer unit in it , what sort of MCB, RCD or RCBO can be used to protect the shed supply cable from the house ?

Would it be OK to protect the shed supply cable with a Type 'C' 100ma RCBO of suitable current rating at the house consumer?

 

[Spark123]

Unless the supply is TT, only the sockets which can reasonably be expected to supply portable equipment outdoors need to be 30mA RCD protected. The supply cable doesn't need to be RCD protected, nor does the shed light.

 

[djhope]

The cable will come straight from the main house consumer unit and then it will connect to a Garage Consumer Unit (Screwfix Ref 63138). I hope that this would provide enough protection?

Thank you

 

[djhope]

Forgot to say that my current shed which is next to the house is currently supplied from the house consumer unit using a M6 Type 1 16a MCB. This has been fine using 2.5mm twin + earth cable. Now due to a extension I need to move the shed to the bottom of the garden. I hope that this bit of extra information will be useful. Many Thanks

David

 

[vsynth]

Using 2.5mm T&E and assuming the cable run is 40metres the maximum amount of current you could supply (dependant on installation method) would be about 12.6 amps or 2.9kW.

4mm T&E would give you about 20.8 amps or 4.8kW.

I plan on doing a similar job myself soon but I will opt for a 40A supply using 10mm SWA.

 

[DESL]

Apart from volt drop calculations you need to be aware of correct method of earthing outbuilding

read this http://www2.theiet.org/Publish/WireRegs/WiringMatters/#16

 

[ban-all-sheds]

It's a shed at the bottom of the garden - it's unlikely to have any extraneous conductive parts...

 

[djhope]

4mm cable sounds good. Any ideas on a good supplier.

Thank you very much for all your comments

David