Which part of a circuit breaker causes or signals the unlatching of the contact mechanism due to an overcurrent?

• A. Trip Unit
• B. Handle Operator
• C. Latch Assembly
• D. Arc Chute

Answer: (A)

Overcurrent protection starts with sensing and deciding to interrupt. The Trip Unit is responsible for detecting excessive current (from thermal or magnetic elements) and issuing the trip signal when a fault is found. That signal activates the tripping mechanism, releasing the latch that holds the contacts closed. Once the latch is released, the contacts separate and the circuit opens. The manual handle operator is for manual control, not automatic fault sensing; the latch assembly simply holds or releases the contacts once the trip signal arrives; the arc chute is there to manage the arc after opening. So the Trip Unit is the part that causes or signals the unlatching due to an overcurrent.