HMI & peripherals
Breaker
Protects the controller cabinet wiring from overcurrent and provides a lockable disconnect point for service.
The main breaker protects the cabinet's internal wiring from overcurrent conditions and, on most installations, doubles as the lockable disconnect point technicians use to de-energize the cabinet for lockout tagout procedures before service.
Breaker sizing is matched to the cabinet's expected load with margin for inrush current at power-up, and an undersized or aging breaker can nuisance trip under normal startup conditions well before any real fault exists.
Because it is a mechanical device with moving contacts, a breaker's trip characteristics can drift with age, which is why periodic testing rather than assumption is the recommended practice for critical installations.
Related components
Common questions
- What does the Breaker do?
- Protects the controller cabinet wiring from overcurrent and provides a lockable disconnect point for service.
- How does the Breaker fail?
- Common failure modes: Nuisance tripping from drifted trip characteristics with age, Contact wear increasing resistance and localized heating, Failure to trip under an actual overcurrent condition, Mechanical wear preventing reliable manual operation.