Ring Main A ...32A RCBO
G/F Kitchen (incl. fridge/freezer)

Absolutely do not put your fridge/freezer on an RCBO circuit, unless you
like coming home from holiday to a rotting stinking mess. It is better to
put it on its own circuit, or at least shared on another MCB only circuit.
You can always cut out one of your lighting circuits to make room.

Ring Main B ...32A RCBO
G/F Dining Room, Lounge, Hall

OK.

Ring Main C ...32A RCBO
1/F Bedrooms, Bathroom, Landing

OK.

Ring Main D ...32A RCBO
Extension: Playroom, Utilities (washer/dryer), Study

OK. Although containing high current devices, having just a washing and a
dryer on the circuit shouldn't cause any overload.

Radial C ...6A MCB
Lights in extension

Might be overkill, could probably combined with another lighting circuit.

Radial D ...32A MCB
Cooker

OK.

Radial E ...16A RCBO
Immersion Heater/boiler controls/pumps

Use an MCB, rather than an RCBO. Although an RCBO is less prone to nuisance
trips than a shared RCD, there's still a chance of a spurious pop when you
are on your winter skiing break, leading to your house freezing, possibly
causing damage.

Radial G ...20A RCBO
Garden sockets & lights

OK.

Assuming that the RCBOs are double width, I guess that I need at least a
17-way consumer unit. Did you put your RCBOs side-by-side? I read
somewhere
on this NG that a RCBO can "trip" an adjacent RCBO.

You can put them side by side, no problem. When populating the consumer
unit, it is best to order as reducing ratings, starting with the heaviest
circuits next to the incomer. Remember that with an RCBO installation, you
want a "standard" isolator incomer (except for TT), rather than a fancy
split load unit.

The garden lights must be switched on/off from the house. The shed
sockets/lights must be switched on/off in the shed. Is it still OK to run
the whole lot off one circuit ("Radial G", above)?

Absolutely. Consider having a DP switch (or even FCU) on the run to the
shed. Then you can ensure that everything is turned off without having to
brave the weather.

My earthing system is TN-S. I guess you'd advise that I would be better
served by a switch than a 100A/100mA time delay RCD at the incomer.

Yes.

So, with these modifications, you get:

1. B32A RCBO - Kitchen ring
2. B32A RCBO - Reception ring
3. B32A RCBO - Upstairs ring
4. B32A RCBO - Extension/utility ring
5. B32A MCB - Cooker
6. B20A RCBO - Outside
7. B16A MCB - Heating
8. B16A MCB - Fridge/Freezer
9. B6A MCB - Lighting A
10. B6A MCB - Lighting B
11. B6A MCB - Alarm

I make this 16 outgoing ways using double width RCBOs, or 11 outgoing ways
using single width RCBOs. You've probably got some overkill on the ring
mains and could combine some, too. For example, you might swap the Utility
RCBO for a 32A MCB for just the appliances and use the Reception ring RCBO
to cover the sockets in the extension. This would save you an RCBO (and give
you an extra way if using double width units). It also removes likely earth
leakage culprits (i.e. the washing machine and tumbler) from the general
purpose ring main.

Christian.