Leaving Certificate Physics Practice Test

RCD stands for Residual Current Device. It protects you from electric shock by monitoring the current in the live and neutral wires and looking for any imbalance. Under normal conditions the same current flows in and out, but if some leaks to the earth—through a person or faulty insulation—the two currents don't match, creating a residual current. The device detects this and rapidly disconnects the circuit, typically at a safety threshold around 30 mA, to prevent harm. The other names aren’t standard terms for this safety device, which is why Residual Current Device is the correct description.