restströmen

Restströmen, or residual current, is the portion of electrical current that does not return through the intended circuit path. In a normal alternating current system, the current in the live conductor should be equal to the current returning in the neutral conductor; any difference is the restströmen. This leakage can arise from damaged insulation, moisture, capacitive coupling, or unintended paths to earth or other conductors.

The magnitude of restströmen is measured as an imbalance between live and neutral currents. Protective devices monitor this imbalance in real time and can interrupt power when the residual current exceeds a set threshold. In domestic installations, common protection values are around 30 milliamperes, with response times typically under 40 milliseconds. Higher thresholds may be used for fire protection or equipment protection, and some devices combine residual current protection with overcurrent protection in a single unit known as RCBOs.

Restströmen can be caused by several factors, including worn insulation, faulty wiring, damp environments, and the presence of powered devices with leakage paths. Even healthy equipment can generate small leakage currents, especially at higher voltages or with modern electronics that use EMI filters or capacitive coupling. Design goals aim to minimize leakage through proper insulation, shielding, grounding, and enclosure design, while ensuring that protective devices can rapidly isolate faults.

Standards and standards-based devices govern leakage protection, testing, and installation practices. Relevant references include the IEC 60364 family for electrical installations and standards for residual current devices, such as IEC 61008 and IEC 61009, which cover RCDs and RCBOs respectively. See also earth leakage, RCD, RCCB, and RCBO.