In LADWP practice, what is the difference between a circuit breaker and a disconnect switch?

In LADWP practice, what is the difference between a circuit breaker and a disconnect switch?

• A. A circuit breaker can isolate a circuit without interrupting current; a disconnect interrupts fault current.
• B. A circuit breaker can interrupt fault current and provide protection; a disconnect switch only isolates and does not interrupt current.
• C. A disconnect switch provides protection by interrupting fault current; a circuit breaker only isolates.
• D. There is no functional difference; both interrupt fault current and isolate the circuit.

Answer: (B)

The key idea is that these devices serve different roles: protection versus isolation. A circuit breaker is a protective device that senses abnormal current (like a short circuit or heavy overcurrent) and automatically opens the circuit to interrupt the fault and protect equipment and personnel. It can interrupt fault current and is designed to trip under fault conditions. A disconnect switch, by contrast, is meant to provide a safe isolation point for maintenance or to de-energize a section of the system. It is not intended to clear faults or rely on for protection. It does not trip to interrupt fault current in normal operation. In practice, you rely on the circuit breaker to interrupt faults; the disconnect is opened only to provide a visible, safe isolation after the fault is cleared and the circuit is de-energized.

The key idea is that these devices serve different roles: protection versus isolation. A circuit breaker is a protective device that senses abnormal current (like a short circuit or heavy overcurrent) and automatically opens the circuit to interrupt the fault and protect equipment and personnel. It can interrupt fault current and is designed to trip under fault conditions.

A disconnect switch, by contrast, is meant to provide a safe isolation point for maintenance or to de-energize a section of the system. It is not intended to clear faults or rely on for protection. It does not trip to interrupt fault current in normal operation. In practice, you rely on the circuit breaker to interrupt faults; the disconnect is opened only to provide a visible, safe isolation after the fault is cleared and the circuit is de-energized.