If you look around the internet, you'll find a vast amount of discussion about this, particularly in relation to whether or not the 'functional earth connection' is actually needed (apparently some people/electricians initially cut them off!).Now that's an interesting difference I had forgotten - and I wonder why it is ?
The RCD protection function itself does not require an earth, and I'm fairly confident the earth wire on an RCBO is only used for generating a test current imbalance*. So I wonder why they decided to do the test current to earth in an RCBO but to neutral in an RCCD.
There is no doubt that under 'normal' circumstances an RCBO will work without an earth connection. The reason for it is usually said to be that if the supply loses its neutral, the 'RCD' part of the RCBO may/will not work - and the most common reason suggested for this is that, in the absence of a neutral, there is/may not be enough pd between L & N to generate the necessary voltage for powering the electronics and that, in some way, if that happens, it can use the L-E pd for that purpose...
...a very credible argument. However, it leads to another question. If, as has been said, a RCD also contains much the same electronics, why is the same not true of an RCD!
Kind Regards, John.
