Overlastbeskyttelse

Overlastbeskyttelse refers to the set of measures and devices used to prevent damage to electrical installations when a load becomes excessive. Its primary purpose is to avoid overheating, insulation damage, fire hazards, and premature wear of equipment by interrupting current before damage occurs.

The protection is implemented with devices such as fuses, circuit breakers, and thermal or magnetic overload relays. Fuses provide a fuse element that melts when the current is too high, causing permanent interruption. Circuit breakers can be reset after tripping and are commonly used for recurring protection in distribution boards. Thermal overload relays monitor motor current and, together with temperature sensing, trip when overheating indicates overload. In motor circuits, protective relays and control gear are used to provide selective and coordinated protection.

Operation is based on monitoring current and sometimes temperature. If the current exceeds a device’s rated value for a specified time, the protective element opens the circuit. Time-current characteristics determine selectivity, balancing fast response to faults with avoiding nuisance trips during normal operation. Distinguishing an overload from a short circuit is essential: short-circuit protection typically acts faster to handle very high fault currents, while overload protection addresses sustained excess load.

Applications include electrical installations in households, commercial buildings, and industrial plants, where overload protection safeguards conductors, transformers, and equipment and reduces fire risk. Proper design involves correct conductor sizing, appropriate trip settings, and coordination between protection devices.

Standards and best practices guide overlastbeskyttelse, with references such as IEC 60364 and IEC 60947 in many regions, and national codes like the NEC in the United States. Regular maintenance and testing of protection devices, including inspection of connections and replacement after faults, are essential for reliable protection.