Residualstrom

Residualstrom, commonly known as residual current or residual-current protection in English, refers to a leakage current that escapes from a circuit to an unintended path, such as the earth. In electrical installations, the current flowing through the live conductor should return through the neutral conductor; any difference indicates leakage, which residual-current protection aims to detect and interrupt.

Residual-current devices (RCDs) or residual-current circuit breakers (RCCBs) are protective devices designed to disconnect a circuit when the residual current exceeds a predefined threshold. Typical residential protection uses around 30 milliamperes to reduce the risk of electric shock. Higher thresholds (for example 100 or 300 mA) may be used for equipment protection or fire prevention. Some devices combine residual-current protection with overcurrent protection and are called RCBOs (residual-current circuit breakers with overcurrent protection).

Operation is based on a current transformer that encloses the live and neutral conductors. Under normal conditions the currents cancel, but any leakage creates an imbalance that the transformer detects, triggering the switch to trip within milliseconds. RCDs can be plug-in, fixed, or part of a distribution board, and many units include a test button to verify functionality.

Applications and standards: RCDs are widely used in residential, commercial, and industrial settings, especially in damp or high-risk areas such as bathrooms, kitchens, outdoors, and workplaces. Standards governing their performance and testing include IEC 61008 (RCCBs) and IEC 61009 (RCBOs), with regional implementations under EN/IEC regulations. Regular testing and periodic inspection are recommended to ensure proper operation.

Limitations: While effective against electric shock and many leakage-related faults, RCDs do not protect against all electrical faults, such as short circuits between live conductors that do not involve earth leakage. They should be used alongside proper insulation, grounding, and other protective devices.