What’s a fuse then?

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)

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2 Responses to What’s a fuse then?

  1. gamegetterII says:

    The U.S.explanation…
    That outlet is called a ground-fault circuit interrupter (GFCI) or sometimes GFI over here.
    When you look at a normal 120-volt outlet in the United States, there are two vertical slots and then a round hole centered below them. The left slot is slightly larger than the right. The left slot is called “neutral,” the right slot is called “hot” and the hole below them is called “ground.” If an appliance is working properly, all electricity that the appliance uses will flow from hot to neutral. A GFCI monitors the amount of current flowing from hot to neutral. If there is any imbalance, it trips the circuit. It is able to sense a mismatch as small as 4 or 5 milliamps, and it can react as quickly as one-thirtieth of a second.
    From here…

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