When developing a test and tag program I am often asked ” What is RCD testing? ”
Residual current devices, or RCDs as they are more commonly called, are important safety devices that can save your life.
Here is a very short, non-technical explanation of how they work and what they do.
An RCD is a device that measures how much current is flowing on the active/live conductor and the neutral conductor of a circuit or appliance. These values should be the same or very close to being the same. If there is a variation, there could be current flowing to “earth” which means there could be a defect in the circuit or an appliance connected to it. When the variation between the active and neutral readings is greater than a specific value the RCD will “trip” and shut off the power supply to that circuit. When that happens the user of the appliance is protected from a potential electric shock.
RCDs will only protect you if they are working and react (trip) fast enough. To ensure the RCD is functioning correctly it must be tested on a regular basis. This requires specialised test equipment and testing procedures. The procedure involves simulating a defect and measuring the trip time to within 1/1,000th of a second.
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