It will be supplying 3 No. strip double fluorescent lights, 3 No.

3A ish

internal double sockets, 1 No. external double socket and a water-butt

20A ought to be plenty

pump (only used occasionally though). The maximum amount of things I
will be using at the same time would be a couple of battery chargers, a
circ saw and the lights.


In fact 20A would do the whol building just fine then.

Questions:

1. Can he utilise a spare 32A MCB running through a 80mA RCD on my CU
in the garage?

Yes, and sort of. Do you mean 80A RCD or 80mA Trip RCD? The former is a
common total current rating for some RCDs, the latter would be an "odd"
trip threshold (30mA or 100mA being far more common). For sockets that
may reasonably be used for powering appliacnes outside, then you really
want the sockets protected by a RCD with a 30mA trip current. (the total
current carrying capacity is not relevant here).

3. What size of cable would be required on this 55m run with, what I
assume will be, a huge voltage drop?

6/10mm SWA for 20/32A circuit.

4. Can he install a switch within the kitchen to turn off the supply
when I'm not in the shed? (This is to avoid the local thieving chavs
nicking my juice!)

Yup

5. Can he install T&E through the house and changing at a weatherproof
junction box on the external kitchen wall, to save on the cost of using
Armoured all the way?

Yup

6. Will he insist on a separate CU in the garage running from the
meter? (More money though to get electricity board involved)

Noe, and whay would that involve the electricity board anyway?

7. Is it necessary to have a CU with separate breakers in the shed to
control/isolate all the different components?

It is adviseable - at least to separate the ligting circuit from the
sockets. Also see below.

Any advice would be welcome to avoid being taken for a ride.

Since you want to use a circular saw in the shed you ought to pay close
attention to what happens under fault conditions. When you accidentally
snag your cable and end up with the saw kicking back at the same time as
it trips the RCD, do you really want to be plunged into darkness?

The solution may be to run the cable from a non RCD protected supply
[1], and then include a RCBO for the power circuit in the shed CU. That
way a fault on the socket circuit will not kill the lights.

[1] You did not mention what type of earthing you currently have in the
house, there are two particular implications that spring to mind:
Firstly you may *need* an RCD at the head end for protection of the SWA
and shed CU from phase to earth faults. In which case using a time
delayed one would be stongly advised so that the downstream on can
discriminate socket circuit faults and trip first before the upstream
one looses your lights. At the distance you are talking about you will
probably want to make the shed a TT install anyway, however if you have
PME setup in the house, you may find it very difficult to meet the
standards required in the shed to export the house earth anyway and be
forced to go TT.

--
Cheers,

John.

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