Q7Power System - I
Question
Q.7. What is the difference between Isolator and Circuit Breaker?
Answer
An isolator is a manually operated, off-load switch used only to provide a visible, physical isolation gap for safe maintenance access after a circuit has already been de-energized, whereas a circuit breaker is an automatic device capable of safely making and breaking both normal load current and fault current under energized conditions.
An isolator (disconnector) is a simple, manually operated mechanical switch with no arc-quenching capability, designed only to be operated when the circuit is already de-energized (no-load, no-current condition), providing a clearly visible physical air gap to ensure safe isolation of equipment for maintenance — attempting to open an isolator under load current would cause a dangerous, sustained arc since it has no interrupting mechanism. A circuit breaker, by contrast, is an automatic switching device equipped with an arc-quenching medium (oil, SF6, vacuum, air) and mechanism specifically designed to safely make and break both normal full-load current and abnormally high fault current, typically operated automatically via a protective relay signal, and includes the necessary arc-interruption capability that an isolator lacks entirely.