Which statement describes the main breaker role in LV service?

• A. The main breaker provides overcurrent protection and a disconnect for the main service.
• B. The main breaker sets the service voltage.
• C. The main breaker acts as a fuse.
• D. The main breaker is used for routine grounding.

Answer: (A)

The main idea here is that the main breaker serves as both the overcurrent protection device and the main disconnect for the service entrance. It is sized to the service rating and will trip if the current exceeds its limit, protecting conductors and equipment from damage due to overloads or short circuits. It also provides a clear way to disconnect the entire service for maintenance or emergency isolation. The voltage of the service isn’t set by this breaker; it’s determined by the utility supply and the service configuration. It isn’t a fuse—breakers and fuses both protect against overcurrent, but a breaker is resettable and operates differently. And routine grounding isn’t done through the main breaker; grounding is provided by the equipment grounding conductor and the grounding electrode system.