In article ,
"Christian McArdle" writes:

As an example, my house has the following circuits installed into a 16
outgoing way Contactum CU. TN-S earthing, 100A DP switch incomer. (60A
cutout). RCBOs are double width, as they were the cheapest Type B RCBOs I
could find.

Mine's pretty identical to yours. House was originally rewired
around 1970, although the original Wylex CU was probably older.
Cabling still perfect, but sockets were crap quality and worn out.
Completely rewired kitchen and bathroom during refit and brought
service and bathroom bonding up to spec and fitted new CU. Most
of the ground floor lighting has been rewired as a side effect
of bringing it under home automation control.

4. B32A MCB. Radial circuit for kitchen fixed integrated appliances.
(dishwasher, washing machine, dryer) remotely switched sockets concealed
under worktop.

5. B16A MCB. Radial circuit for fridge/freezer only. Reduces risk of
defrosting, as only a fault on that circuit, or the main service fuse will
cut the power.

These two I have on one circuit, but not RCD protected.

7. B6A MCB. Most of house lighting circuit.

8. B6A MCB. New lighting circuit (kitchen only currently)

I would suggest using C6A for lighting circuits. It may reduce
the chance of a filament lamp tripping the MCB. BS1361 cartridge
fuse is another option (probably a better option).

9. B6A MCB. Alarms (Interlinked smoke/heat detectors + intruder alarm)

If I had an electric hob, there would be a separate B32A MCB circuit for it.

I put the circuit in although I don't ever intend having an
electric hob myself. For now, it has an unswitched 13A socket
on the end with the gas hob spark generator plugged into it,
and a 45A cooker switch ;-)

I would also split the rest of the house ring main into two.

Strangely, the 1970 rewire did install two ring circuits, but they
were joined into one big ring in the CU, which also makes me think
the CU was older and not changed at that time.

B. The relative merits of RCDs and RCBOs.

30mA RCD (whole house) = BAD!!!

and doesn't conform to the regs

30mA RCD (split load) = Much cheaper than RCBOs

30mA RCBO = Much less prone to nuisance tripping. Tripping has fewer
consequences. Warm feeling of having done it right.

One disadvantage of most RCBO's is they give no clue what tripped
them, earth leakage or current draw. There were some types where
the dolly only moved halfway to the off position when the RCD part
caused the trip, but I haven't seen them for a long time now.

As for your list of appliances:

electric cooker = Own dedicated circuit on B32A MCB. Do not install cooker
unit with built in socket. They look bad and trail leads over the cooker.

....and the cooker doesn't want RCD protection, but all the worktop
sockets do, which is incompatible with a combined socket.

boiler = put on a dedicated central heating circuit MCB (not RCBO). Can
share with immersion, especially if sharing controls, such as programmers.
All central heating valves, programmers and other controls should be from
the same central heating circuit.

Moreover, all the central heating controls should all be switched off
by the one boiler isolation switch.

fire alarms = either wire from a regularly used lighting circuit, or give
own small radial circuit (i.e. B6A or B3A MCB).

There are some rules (which I don't remember, and didn't seem very
sensible to me) about sharing smoke detectors with lighting circuits,
and relate to the type of battery backup the smoke detectors have.
In my case, the smoke detectors run off the alarm anyway, and use
the alarm battery in the event of a mains failure.

--
Andrew Gabriel