Is it possible to put a 16mm swa on a 40a mcb protected by an rcd

[brianmoooore]

It will just be rcd protected at the incoming point and then mcbs at the other end

Poor design. SWA doesn't need protection by a RCD, since there's very little likelihood of making contact with the live conductor, without shorting it to earth, in which case the OCD will take care of things.
Ideally this should be a fuse rather than a MCB, to provide discrimination between it and the MCBs or RCBOs at the load end.

 

[timhoward]

Additionally, it would be better if a fault on the circuits the far end didn’t take out half the house too.