Fused spur Q

[RickH]

Got a friend asking me if he can put power to his shed ... the run from the shed to the nearest ring main socket is around 20m.
I know Section 7.2.2 of the OSG says 'as a rule of thumb for rings, unfused spur lengths should not exceed 1/8 the cable length from the spur to the furthest point of the ring'
This 20m will exceed this ..... but if this done as a fused spur then the overriding factor would be voltage drop.
20m at Max 13A would be served by 1.5mm ...... if upsized for a bit of safety factor to 2.5mm, if there anything stopping this approach being used.

Assumes RCD protected ring .. otherwise would make fused spur RCD protected.

 

[JohnW2]

I know Section 7.2.2 of the OSG says 'as a rule of thumb for rings, unfused spur lengths should not exceed 1/8 the cable length from the spur to the furthest point of the ring'

The OSG invented that one. The regulations themselves (BS7671) say no such thing, and I personally can't see and sense or logic behind what the OSG says.

Kind Regards, John

 

[RickH]

So if I suggest the fused spur route - then all I need to really worry about is voltage drop.

 

[JohnW2]

So if I suggest the fused spur route - then all I need to really worry about is voltage drop.

I wouldn't say 'all'.

You also need to 'worry about' whether the socket from which you intend to take the spur is actually 'on the ring' (rather than being a spur itself), and also what type of cable we are talking about, and how it is going to get from the house to the shed.

Kind Regards, John