RCD or fuse box in home

hi Eddie this question is little bit weird , but I will try to explain RCD - is a residual current device , is a device installed in consumer unit / fuse box/ for faulty protection usually You have dual RCD consumer units - that's mean so two RCD device are placed in Your consumer unit but very often electrician use RCBO instead if MCB , then all circuit have an " independent RCD " itself ...and in that situation , You can say , You have 20 RCDs in Your consumer unit regarding to the amount of consumer units , that depend from designer , sometimes one property has only one consumer unit , sometimes more than one / for example one for each floor.../

You can have inline RCD's yes, however, to avoid nuisence tripping the RCD down the line would need to be of a more sensitive mA rating so not to trip the RCD in the house or in other words the house RCD in the house made to be a time delayed RCD. (s-type).