neutrals in CU

[Spark123]

Most domestic circuits now require 30mA RCD protection owing to the way the cables are installed, one thing you need to take into consideration is what happens should an RCD trip. It is no good if a single RCD feeds a whole installation - a simple fault on an appliance can plunge the whole house into darkness.
Using RCBOs is one option, using a board with more than one RCD with sockets and lights split i.e. down sockets and up lights on one RCD and up sockets and down lights on the other is another option.
You need to remember that only the neutrals from the circuit supplied from an RCD connect to the neutral bar for that RCD - if you start mixing them up then the RCD will not hold in.

 

[Paul_C]

View media item 20623
That better

If you were going to do that though, you might just as well remove the D.P. switch altogether, move the RCD into its place as the main, and give yourself a couple more spaces for MCB's.

 

[ColJack]

This is my thinking

Split load board, some circuits RCD protected some not.
Link out the neutral bar so all circuits RCD protected. Not an ideal situation but is it better to be RCD protected or not?

nope, think again..
if you run RCD and non RCD neutrals to the same bar then there is neutral current goung through the RCD that didn't come from the RCD live, and will trip the RCD.

if it's split load, each RCD will require a seperate neutral connection ( be it bar or terminal in the case of RCBO ), and the non RCD will require their own neutral bar / connection.