vikavirtasuojia

Vikavirtasuojia, known in English as residual current devices (RCDs) or residual current circuit breakers, are protective electrical devices designed to reduce the risk of electric shock and electrical fires. They monitor the current flowing in the live and neutral conductors of a circuit and trip the circuit if a leakage current to earth is detected.

The core principle is differential current sensing. Under normal operation the current entering a circuit equals the current leaving it. If some current leaks to earth through a person or a fault path, the imbalance triggers the device to interrupt power within a fraction of a second. The sensitivity, expressed as IΔn, commonly ranges from 30 milliamps for personal protection to higher values for equipment protection. RCDs may also have additional features such as overload and short-circuit protection when combined with other protective devices.

RCDs come in several types depending on the waveform of the leakage current they can detect. Type AC devices respond to alternating leakage, Type A to AC and pulsating DC, and Type B to AC, pulsating DC, and smooth DC up to higher frequencies. Type F and other variants cover mixed leakage characteristics. They are typically installed at main distribution boards or sub-panels to protect individual circuits, bathrooms, kitchens, and outdoor installations.

Important limitations include that RCDs do not protect against overcurrent or short circuits by themselves; they respond only to earth leakage. They can nuisance-trip with certain high-frequency or complex leakage currents. Regular testing, often via a built-in test button or a dedicated tester, is recommended to verify proper operation. Standards for RCDs in many regions follow EN 61008 or related specifications.