SWA Sizing?

[Greenie9657]

Hi All

Im in the process of planning and buying all the bits I need ready for when my drive gets ripped up I can get SWA laid to my bricked shed. I thought I needed 6mm SWA but after doing some digging around some have suggested I could get away with 2.5mm. Isnt that a bit low? and that's doing calculations using 5kw.

Im happy maybe using 4mm but 2.5 just seems a bit small. The shed is around 8 meters away from the house and I was going to run 6mm (t+e) from the house CU to the outside wall then join it to the SWA for the journey outside.

I guess looking at it 5KW of power is 21A so 4mm and a 32MCB would be fine to allow for any extras. 6mm on a 40MCB is almost 10KW which is a little overkill I suppose. (allowing for the 8 meter run as well).

What do you guys think? Hope it all makes sense.



Many thanks

 

[DaftPunk]

For the difference in price it's not worth trying to get away with a small cable.

Just put the 6 mil in and you know you're good to go.

 

[bernardgreen]

Don't forget a separate duct for cables for data, telephone intercom alarm etc etc

 

[Greenie9657]

Thanks for the reply daft. Is the 40MCB fine? It's more than enough for what I want but if the cable carries it I might as well hadn't i? I could then wire outside light from the garage CU I guess.

 

[JohnW2]

Thanks for the reply daft. Is the 40MCB fine? It's more than enough for what I want but if the cable carries it I might as well hadn't i? I could then wire outside light from the garage CU I guess.

If you're having a CU in the garage, with MCBs for each final circuit, it's probably best that you stick with the 40A MCB - since there is then at least some hope that you might get 'discrimination' between that and the garage MCBs. However, if you used a 32A MCB, you could then dispense with the garage CU, wiring the socket(s) directly from the feed, using 4mm² cable, with an FCU (probably with a 3A fuse) off that for lighting.

Kind Regards, John

 

[Greenie9657]

Thanks john. My garage is similar to the second option at the minute but I just wanted a dedicated MCB for garage when I finally get round to sorting it. Some people say there's no point RCD protecting the 40MCB in the house CU if the garage will have one. Do you agree? I was gonna do it just so there is protection for the wire going into the garage.

 

[EFLImpudence]

Thanks john. My garage is similar to the second option at the minute but I just wanted a dedicated MCB for garage when I finally get round to sorting it. Some people say there's no point RCD protecting the 40MCB in the house CU if the garage will have one.Do you agree?

If you use armoured cable that is so.
You don't want the one in the house to trip when you are in the shed.

I was gonna do it just so there is protection for the wire going into the garage.

If you were to use unarmoured cable with installation methods which require RCD protection then you must.