Power to summer house - futureproof cable size

[mbelectric]

My grandad wants me to put power into his summerhouse. It is 25m from the garage where the (RCD Protected with spare way) consumer unit is situated. He just wants a couple of double sockets in the summer house for a computer (and periphials) and a table lamp. Apart from a small section under a path there is a brick wall the rest of the route for the SWA to be affixed. Taking into account the distance, voltage drop and load I reckoned 2.5 SWA would be ok. However, given the fact my grandad won't live forever and someone may have a different use for the sockets in the future would it be wise to go for 4mm or even 6mm just in case or is this 'what-if' scenario something I need not concern myself with.

BTW I know about the Part P notification.

 

[Chri5]

The load limit of the SWA will have to be restricted to the size of the fuse that the sub board in the garage can take.

There's nothing wrong with a larger cable instal for future use, but before the potential limit of the larger cable could be used an upgrade maybe required between main board and garage sub board.

e.g. say you have a 40a supply between the house and garage, that may have a 6a lighting circuit and a 20a radial for garage sockets. So if you have a 32a supply added it may overload the designed use of the sub board.
Diversity can be applied, but there is still the chance of overload and it would be better to fuse the SWA at 20a (and why then get a SWA that take anymore than 20a).

 

[plugwash]

My grandad wants me to put power into his summerhouse. It is 25m from the garage where the (RCD Protected with spare way) consumer unit is situated.

Is this consumer unit in the garage the main CU for the house or a sub CU? if the latter how exactly is it fed? (cable size, length, type, breaker rating etc)

 

[mbelectric]

Sorry, I should have been more specific. The consumer unit in the garage is the main consumer unit.

 

[Click-Sure]

Bigger the better as far as the SWA is concerned, provide overcurrent protection (fuse/mcb) appropriate for the current design load, say 20A, then if the design load changes the overcurrent protection arrangements can be re-assessed at a later time.

 

[Spark123]

No electric heater? Might be better looking into running something like a 4mm or 6mm and put another CU in the summerhouse.
Oh - and don't forget the photos!

 

[plugwash]

6mm would seem appropriate to me, given the distance we have here it would be enough to support a 32A circuit which should be plenty for most outbuilding needs.

 

[ban-all-sheds]

And the extra initial cost of 10mm² vs 6mm² in proportion to the overall cost of the job, and weighed against the cost and inconvenience of ever having to replace the cable is......?