First came the how does a RCD work, then came the basics.
SWMBO had incorrectly deduced that a RCD was a type of fuse.
So here’s fuses in a nutshell.
A fuse is a (non resettable) safety device consisting of a strip of wire that melts and breaks an electric circuit if the current exceeds a safe level aka an overload. A few examples of UK fuses. It’s job is to prevent fire damage to the cabling and equipment.
A circuit breaker is an automatic device (resettable) for stopping the flow of current in the event of an overload (fault) in an electric circuit or device as a safety measure. It’s job is to prevent fire damage to the cabling and equipment.
A RCD or residual current device constantly monitors the electric current flowing through one or more circuits. It DOES NOT react to dangerously high currents aka an overload so cannot replace a fuse. If it detects electricity flowing down an unintended path it switches the circuit off. It’s job is to prevent harm to a user and/or a fire.
A RCBOs combines the functions of a contact breaker and a RCD in one unit.
It is resettable.
They are used to protect a particular circuit, instead of having a single RCD for the whole building. It’s job is to prevent HARM to a user, and to cut off excessive current aka an overload that may lead to damage to the cabling and equipment.
Outwardly they look the same (occasionally a bit more “chunky”) as a RCD.
English to American.
Yep, translation is needed.
Basically because little is standard in our world.
An RCD is known as a GFI (Ground Fault Indicator) in the US and Canada
Or an ALCI (appliance leakage current interrupter)