A thermal-magnetic circuit breaker for a 300 KW alternator is rated at 500 amperes at full continuous load. Which of the following conditions will trip the breaker?

Correct Answer: Option A — Instantaneous current draw of 5,000 amperes.

Thermal-magnetic breakers feature dual-action protection. The magnetic trip unit instantaneously responds to massive short-circuit currents like 5,000 amperes, overriding thermal time-delays designed to handle safe, temporary overloads. This rapid interruption prevents severe electrical damage and switchboard fires aboard vessels.