I've read the 'power to the shed' threads, but...

[charliegolf]

... if I want a few lights, and the opportunity to use a power saw or drill, would it be within the regs to have an electrician spur off through the wall from a socket in the house; run 40m of 2.5mm^2 swa and Bob's your uncle?

Professional responses seem to suggest 6 or 10mm^2 cable

(Confession: before the regs on notifiable work came in, I ran 2.5 mm^2 swa to a Screwfix cu in the garage 5-6m away. Laid in 4 double sockets and a light fitting and connected it to the house cu. Myself! Nothing has burned down or tripped out as a result in 16 years!)

CG

 

[ban-all-sheds]

... if I want a few lights, and the opportunity to use a power saw or drill, would it be within the regs to have an electrician spur off through the wall from a socket in the house; run 40m of 2.5mm^2 swa and Bob's your uncle?

Probably not - voltage drop would be too high.

Professional responses seem to suggest 6 or 10mm^2 cable

If you assume the design current for a spur is 13A, you'd need 4mm² for that distance.

(Confession: before the regs on notifiable work came in, I ran 2.5 mm^2 swa to a Screwfix cu in the garage 5-6m away. Laid in 4 double sockets and a light fitting and connected it to the house cu. Myself! Nothing has burned down or tripped out as a result in 16 years!)

Did you test it all so that you know that the protective device would have operated if needed?

 

[charliegolf]

Thanks for the reply. The reason I asked the Q in the way I did, is because my house cu is full, and I don't want to go to the expense of replacing it for a dedicated circuit- itself for only occasional use. Your initial reply, given the correction to 4mm^2, suggests an acceptable solution?

No, I did not get it tested. Should I, after all this time?

 

[sparkwright]

If it's easy to get the cable to the existing consumer, you may as well.

It could be connected to the socket circuit here, in the same manner you suggested earlier.
If you get a new consumer unit in the future, then it can easily be changed so it's on it's own circuit.

Either way will do, but be sure to get appropriate RCD protection.

 

[Iggifer]

Or you take the SWA back to the meter, Split the tails into henleys and terminate the SWA into a metal switchfuse and then replace the DB in the shed. No need to replace the existing CU then, and only local RCD protection.

 

[ericmark]

would it be within the regs

Remember you asked, there are two sets of regulations the building regs which are law and the IET/BSi regs which are not law but may as well be as an electrician has to agree to follow them in order to be a scheme member.

The main limit is volt drop 3% for lights and 5% for power, so 6.9 and 11.5 volt in real terms LED lamps can often run with over a 50% volt drop, and this is the rub even though it will work A1 the regs don't allow it. As to the drill I have worked on sites with 55-0-55 volt supplies and I know they will also work with a massive volt drop.

So with 2.5mm² your limited to 32 meters to keep within 6.9 volt drop and 54 meters for the 11.5 volt drop. With 4mm² it jumps to 54.5 meters for the 6.9 volt drop so well within limits.