swa cable size

[gt67]

Hi,

I am after a bit of help/advice with regards to the correct size swa cable to feed a home office approx 40m at the end of a garden.

Requirement to feed:

• 1 x pc
• 1 x printer
• 1 x ADSL modem
• 1 x monitor
• 1 x lighting cct
• 1 x electric heater (oil filled approx 2.5kW
• 1 x radio

At the moment there is an swa cable feeding 2 garden sheds which caters for 2 x light ccts (1 in each), 4 x sockets. This is fed from the main house fuse board via 2 more fuse boards (assume they are RCD's) but not checked yet as access not yet sorted. I wasd planning to remove this existing cable so it can be fed from existing boards.

So:

Q1 - in your collective opinions and not seeing the site, does this sound acceptable?
Q2 - would 6mm 3 core swa be suitable if it is clipped directly to a wall or is 4mm OK?

Thanks for any help and advice given,

Graham

 

[Spoon]

If you have already power to the sheds then why do you want to change it? What is the size of the existing cable? What MCB rating is to wired to in your house cu?

 

[IQ Electrical]

You will need to consider the earthing system at the origin and whether the distribution circuit cpc will also be acting as a protective bonding conductor to any extraneous-conductive parts in the external buildings.

 

[HandySparks]

A1: When you have access, can you list the complete chain from incoming supply to final ccts in home office? Are you proposing to supply home office and 2 sheds via same cable?

A2: Just from a voltage drop point of view, you'll probably need to go for 6mm². If you have (say) 2500W heater, 1000W PC and other stuff, 500W lighting (any external lighting?), total 4000W, =17A at 230V. This will give 7.7V drop down 40m of 4mm² which is more than the 3% allowed for lighting, even without the volt drop in the house cables and the final ccts.
If you have loads in the sheds at the same time on same cable, may have to go bigger.