As I recall, the customer was supplying 2 outbuildings via the 2 x MCBs. The outbuildings each had an RCBO board.
The TD RCD provided protection for the feed cables to the boards, whilst providing discrimination between the TD RCD and the series connected RCBOs in the boards.
Thanks for the welcome OnOff and I will be happy to answer any questions the Forum may have. I am not here to promote my Company or its products, as I am sure the Moderators would take a dim view of that. If anybody wants more information, please PM me.