What is the difference between an RCD and an RCBO?

An RCD (Residual Current Device) sits in your fuse box and protects several circuits at once. If any one of those circuits develops a fault, the RCD trips and cuts power to all of them — so a fault in your kitchen might switch off your kitchen, living room, and hallway all at once. An RCBO (Residual Current Breaker with Overload) is a smaller device that fits in the same space as a standard circuit breaker and protects just one circuit. If that circuit faults, only that circuit trips — everything else stays on. RCBOs are considered the better solution because they prevent one fault from affecting multiple circuits, making fault-finding much easier. They cost more, so older fuse boards often use a single RCD for several circuits to save money.