pääkytkin

Pääkytkin, in Finnish electrical terminology, is the main switch or main disconnector that controls the power supply to a building or installation. Its purpose is to provide a manual means to completely isolate the installation from incoming power for maintenance, fault clearance, or emergency shutdown. It is not a substitute for overcurrent protection, which is provided by fuses or circuit breakers.

Placement and configuration: The pääkytkin is typically located at the service entrance or inside the main distribution board. It is designed to disconnect all live conductors and is commonly 2-, 3-, or 4-pole to switch L1, L2, L3 (and sometimes neutral) simultaneously. The device should be accessible, clearly labeled, and, where required, lockable to prevent accidental re-energizing.

Ratings and operation: A main switch is specified by its current rating (for example 40–125 A in residential installations) and its breaking capacity. It may be a manual switch or motor-operated, and can be part of a switchgear assembly. Opening the main switch isolates the installation, while protective devices continue to protect individual circuits.

Standards and safety: Installation follows national and international standards for electrical installations, such as IEC 60364 and local regulations. A licensed electrician should install and test the main switch, ensure proper labeling, and verify functionality. Regular inspections help ensure reliable operation and detect wear.

Terminology and context: In practice, "pääkytkin" denotes the isolating device that enables safe access to wiring, while the broader main service equipment may include other protective components. The exact configuration varies by country and installation.