UK Running an additional armoured cable to outdoor building.

[Gazza81288]

Hello,

I am wanting to run some cable down to an outbuilding that will be used as an office (4 double sockets, lights and some sort of heating) I understand I need 10mm armoured cable to be safe. However the power will be taken from my garage consumer box, which in turn is taken from the main board via 2.5mm armoured cable.

However surely if I use 10mm will that just be overkill if it’s essentially taken from the main board with 2.5mm?

 

[James]

Depending on the load and distance, 10mm or even 16mm may be required
It sounds like the garage distribution board is unlikely to be able to supply your requirements.
I would recommend you get a local electrician involved before you buy anything.

 

[EddieB]

It sounds as if your garage DB is exactly that ...only a garage supply. You'll need to get that supply looked at and upgraded for the additional loading required. What size is the breaker back at the main board feeding thee garage?

 

[Marvo]

As above, sounds like you may overload the garage supply and 10mm SWA cable is expensive and might be completely unnecessary. Rather spend the money on getting a decent sparky to give you good advice on a circuit design that will work without overspending and without it becoming an annoyance due to overload issues..

 

[EricMark]

There are a number of factors taken into consideration when selecting cable size.
1) Maximum current.
2) Earth loop impedance.
3) Volt drop or line - neutral - line loop impedance.
So the 2.5 mm² limits the maximum current, the earth loop impedance will depend on supply type, and if there are RCD's etc. The volt drop can be worked out by cable length. To work it out, you need either instruments to test, or the installation certificates for what you have already.