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RJH[_2_]

On 02/01/2019 22:37, wrote:
On Wednesday, 2 January 2019 21:05:07 UTC, RJH wrote:

A friend has build a fairly elaborate shed - about 5m x 5m, insulated.
An electrician has installed a 63A feed from the main supply, using a
consumer unit and an MCB, to the shed (which is 75m from the house),
terminated with a 13A socket, with lighting spurred off the socket.

He's asked me to help him install 6 double sockets and wiring/switching
to 4 x 4' 50W LED batten lights.

I'm not sure yet whether I'm going to do it - I'd do it for myself, but
he's quite impatient, and I don't think he'd be happy with the 3 months
I'd give myself to exercise excessive caution. Anyway, a couple of Qs:

1) Would you use a consumer unit in the shed? If so, what's the MCB and
RCD situation? I's assume the CU and MCB/RCD arrangements at the main
supply have some bearing on this.

You'll want a local earth rod with everything RCDed.

Thanks. I'm loosely assuming there's a local earth rod fitted by the
sparks - but will check.

2) Ring or radial for the sockets? I've had a look at the DIY wiki:
http://wiki.diyfaq.org.uk/index.php/House_Wiring_for_Beginners
I think it's going to need a ring because he's factoring in an oven
(3kW, for pottery) at a later date. But it'd be a lot easier to do a
dedicated oven socket on a separate feed from however (1) is organised,
and a radial for the remaining 5 sockets. I don't follow where the '20A'
in the radial comes from in the wiki diagram - how is a radial socket
circuit designed for a particular use? The only anticipated high current
device is a 2kW heater. But I'd guess contingencies have to be designed in.

Ring has 2 slight advantages over radial: usually a mite cheaper on cable & a bit safer. But either works fine.

3) Routing the wiring. He's intending to use 20mm plastic tube conduit,
which for layout reasons has to go up, round, and down to the
sockets/lights/switches. It'd obviously be neater to route all the
cables in one run of conduit - is there some guidance relating to
stuffing conduit with cable?

see the wiki page on Cable.

Thanks - got that now.

The fact that I'm asking these questions tends towards telling him to
get an electrician - I can see this being a bit of a nightmare. But
answers will help me understand it all better, and give him something to
think about.

Should be no nightmares once you've found out what to do.

It's more the 'client' - he's quite impatient and has a habit of looking
for fault when it isn't necessarily there. A sort of irritatingly
enquiring mind looking for shortcuts.

--
Cheers, Rob