If you've ever stared at your fuse box not knowing what's what, this article is for you
You open the fuse box and see a row of switches, all much the same. You know you need to flip the one that's down, but you're not entirely sure what each one does or why one sometimes trips and another trips at other times. It's a common situation, and understanding it doesn't require being an electrician.
At Iluminamos tu Vida, we explain this many times to our clients when we do a review or installation, because we believe it's useful to know what is protecting your home and how.
The differential: the one that protects you
The RCD is the largest switch on the board, usually the first or one of the most prominent. Its function is to protect you, people, from electric shocks.
What it does is constantly monitor that the current entering through one cable is the same as the one leaving through the other. If it notices a difference, however small, it means that some of the current is going somewhere it shouldn't, for example, through the casing of a faulty appliance or through the wall if there's damp. At that point, the RCD cuts off the power so that this lost current doesn't give you a shock.
When the RCD trips, it's usually because there's an appliance with a small earth leakage or because there's moisture somewhere in the installation. Disconnecting appliances one by one and seeing if the RCD stays on when reset usually helps to identify the culprit.
The circuit breaker: the one that protects the wires
MCBs are the smallest switches, usually there are several in the fuse box, each labelled with the circuit it controls: kitchen, living room, bedrooms, bathroom, and so on.
Its function is to protect the installation's wiring. If too many appliances are connected to a circuit and the current exceeds what that.
When the kitchen circuit breaker trips, for example, you've likely had too many appliances on at the same time: the oven, the ceramic hob, the microwave, and the coffee machine can be too much for that circuit at once.
How do I know which one has tripped?
It's simple: the one that has jumped will be in a different position to the others, usually downwards or in an intermediate position. In well-labelled modern diagrams, you can see which circuit it is, and that already gives you a clue where to look for the problem.
If it trips and immediately goes back down, it means the cause of the tripping is still active. In that case, don't insist: disconnect appliances from that circuit and try again. If it continues to trip with no load, the problem may be with the installation and warrants an electrician's inspection.
What if I don't know which is which on my chart?
In old fuse boxes, there are sometimes no labels, or the ones that are present don't correspond with reality. If this is your situation, at Iluminamos tu Vida we identify and label them correctly when we carry out a review or intervention. Knowing what each switch in your fuse box controls is essential for calmly managing any fault.