Hovedstrømbryder

Hovedstrømbryder, or main circuit breaker, is the primary protective device in a low‑voltage electrical installation that can interrupt current to the entire circuit when protection is required. It is used to disconnect power for maintenance and to provide rapid isolation in case of a fault.

Typically located at the service entrance or within a distribution board, the main breaker offers a visible means to disconnect power. It may be single-pole, double-pole, or multi-pole, and is often operated by a manual handle. In many jurisdictions, the main breaker also serves as the service disconnect and must show a visible open contact when tripped or opened.

Main circuit breakers come in various types and ratings. They include miniature circuit breakers (MCB) and molded‑case circuit breakers (MCCB), rated from a few amperes to several hundred amperes. They have a breaking capacity (Icn) that defines the maximum fault current they can interrupt safely. Tripping mechanisms can be thermal, magnetic, or electronic. The main breaker protects feeders downstream from overloads and short circuits, and is often part of a broader protection scheme that may include residual current devices (RCD/RCBO) and additional branch circuit breakers.

In some installations, a separate main switch is used solely for isolation, while protection is provided by downstream circuit breakers. In others, the main breaker performs both isolation and protection. Standards governing main circuit breakers include IEC 60947-2 for low‑voltage breakers, IEC 60898 for household applications, and national standards such as NEK 400 in Norway.