An RCD, is a device that monitors the electricity supply, and when it detects an electricity leakage, it disconnects the electric supply. Usually it is confused with a circuit breaker, if you look at the pictures below, you can see they are quite similar, but the difference is that the RCD has a test button, while the circuit breaker do not.
Circuit breakers are important, as they protect the installation against a fire hazard i.e. your house will not burn as long as your circuit breakers are working properly.
RCD are even more important than circuit breakers. Why? Because the RCD is the device that protects us from being shocked. If there is an electric leakeage, the RCD will cut the electric power, thus preventing us from being shocked when touching any metallic part of our house (shower, washing machine, microwave, electric heater…)
In Spain the RCD is called Interruptor Diferencial (ID) and it’s the first thing that have to be checked when Iberdrola asks you for a "boletin".
How can I know if my RCD is working?
Every 3-4 months, you should test the RCD by pressing the test button. If the RCD is working proprly, it will trip down and cut the mains suplly. If it doen’t cut the electricity, you should get in touch with an electrician to change it as soon as possible, as you lifes might be at risk.
The worst fault you can have in an electric installation is an RCD fault.
Usually is a pain in the ass for an electrician to find the fault. Many selfcalled professionals, in order to finish quickly, they just bypass the RCD, leaving all the house unprotected, and thus risking the life of you family.
Everytime you hire an electrician you should ask him to show his credential, and remember to ask your invoice, as this is the document that certify that the changes that have been made in your installation are legal, and don’t represent any risk neither for you or for your property.
Also, if your electrical panel is older than 15 years, you should call an electrician to perform an RCD test. It will not take more than 5 minutes, but it can save your life.