UK RCD rating in Sub board less than suppy protection

[misterpotski]

I have a 40amp RCD downstream of a 50a MCB (10mm csa cable) should the MCB be lowered to protect the RCD from overload?
If so why does this not apply to RCD devices in Split Load boards

 

[James]

It depends on what is connected, if it is a shower for instance that is rated at 40A then no, there is no possibility of overload.

 

[misterpotski]

It's a sub DB with potentially 54a Load over 3 circuits (not accounting for diversity)
Main concern although unlikely is the potential to exceed the rating of the RCD before the MCB operates.
However this would seem a more likely thing to happen in the main CCU (Split Load dual RCD board) with a potential to exceed 150amps on that RCD alone. I understand the likely hood of this is remote but still am intrigued as to why both RCDs in the main CCU are not rated at 100a. Just seems a little strange.

 

[newfutile]

In short the (RCD) Residual Current Device must be protected by a suitable overcurrent device. BEAMA issued a technical bulletin about this:

https://www.beama.org.uk/static/uploaded/6861a2e1-d8d4-4d81-b5fa710ba60ca4a7.pdf

 

[misterpotski]

In short the (RCD) Residual Current Device must be protected by a suitable overcurrent device. BEAMA issued a technical bulletin about this:

https://www.beama.org.uk/static/uploaded/6861a2e1-d8d4-4d81-b5fa710ba60ca4a7.pdf

Thanks for the link.
I will have a read.