RCD Diversity?

[kentster]

Hi All

Newbie so be gentle on me. I'm training to be a spark at the moment (early stages) and have a simple question on diversity. I know you can use diversity in regards to overcurrent protection but can you also apply to diversity to RCDs?

Was in B&Q walking round and noticed a massive display of consumer units fully populated with MCBs (1 x 40, 4 x 32, 2 x 16 & 3 x 6A) with the usual 100A main switch but with 2 x 30mA 63A RCDs.

Does this mean that you apply diversity to work out what circuits you can protect by each one?

 

[pushrod]

Anyone know how quickly an rcd cooks if you exceed it's rated capacity. Have you got much leeway and for how long?
Also what is the most likely damage? does it just take out the trip and leave you thinking it is still ok or does it stop it conducting altogether?