Live and Neutral enter my CU from my meter directly into a 80A RCD (MK model
No LN 5780)

Sounds right(via a sealed (metal loops of wire with a lead
like lump on) little box

This is the suppliers seal and should not be brokenthe electricity board to
come out and
disconnect my main fuse so I can install a 100A isolator in between the
meter and the CU,
When they disconnect your supply and you put your isolater in install a henley
block ( connection device for 25 mm tails ) for your outbuilding supply rcd.

There is then some wire connected to the same terminals as the incoming
supply (looks like 2.5mm) that then goes to the input of the lighting RCD
(MK number 6730), this then has three 5A MCB's connected to it that supply

There is then some wire connected to the same terminals as the incoming
supply (looks like 2.5mm) that then goes to the input of the lighting RCD
(MK number 6730), this then has three 5A MCB's connected to it that supply

You have a MK split consumer unit with your ring circuits being RCD protected

Off the 80A RCD are the following MCB's (nearest to furthest)

30A 30A 30A 20A 15A 10A
Have you an electric cooker or electric shower ?
They should be on there own circuits, 45A mcbs

his then has three 5A MCB's connected to it that supply
all the lighting in the house.


Sounds right.My first question is, is this correct - I am concerned that the
wires that
run from the top (inlet) of the first RCD to the inlet of the second
(lighting) RCD are not sufficiently protected (the only thing protecting
them is the 80A electricity board fuse)

If it is an MK split board it should be pre wired and the protection should be
ok


For your outbuildings, I would do it this way, from Henley block 25mm tails to
30ma RCD and 2.5mm to your first building to a consumer unit. If you use a
catenary wire, ( overhead ) it must be earthed at the house end from your main
earthing point. and your 2.5 mm supported every 250mm ( cable ties ) . At the
consumer unit provide an earth using an earth electrode, get this tested, the
earth electrode resistance must be below 200 ohms.
Then design your power circuits, ring circuits protected by 32A mcbs, radials
by 20A mcbs and lighting by 5A mcbs
The 25m garage run if underground should be in SWA using glands to metal boxes
then for extra safety connect it to a FCU.
Hope this has been of help, if you can not understand this e mail me as i have
a great diagram which is very clear and i will send it to you