Residual Current Device

A residual current device (RCD), also known as a ground fault circuit interrupter (GFCI), is an electrical safety device that continuously monitors the current flowing through a circuit and instantly disconnects the power if it detects an imbalance — which indicates that current is leaking to ground, possibly through a person's body. An RCD can disconnect the circuit in as little as 25 milliseconds, fast enough to prevent a lethal electric shock.

RCDs are mandatory in Finnish electrical installations for all circuits serving wet rooms (bathrooms, kitchens, laundry rooms, saunas), outdoor outlets, and any socket circuits in new construction. The standard sensitivity for personal protection is 30 milliamps — meaning the RCD will trip if just 30 milliamps of current leaks to ground. Higher-sensitivity RCDs (10 milliamps) are available for extra protection in high-risk areas.

While RCDs provide critical protection against electric shock, they do not protect against overloads or short circuits — that is the circuit breaker's job. Modern installations often use combined RCD/breaker units (RCBOs) that provide both functions in a single device, protecting each circuit independently. This means a fault on one circuit does not affect others.

RCD function should be tested monthly by pressing the test button on the device. If the RCD does not trip when tested, it has failed and must be replaced by an electrician immediately — a non-functional RCD provides no protection. RCDs can also trip due to moisture in outdoor outlets, faulty appliances, or degraded wiring insulation. If an RCD trips repeatedly, do not simply reset it — have an electrician identify and fix the underlying fault.