What is close excess-current protection?

Close excess-current protection is a specific type of protective relay designed to respond to overcurrent conditions in electrical circuits. The correct choice indicates that this protection mechanism interrupts a fault within a specific time frame, precisely 4 hours, at a predetermined threshold of 1.5 times the rated current.

This timing and current level are critical because they ensure that the protection apparatus can effectively limit damage to electrical equipment and reduce the risk of fire or other hazards caused by prolonged overcurrent. By setting the interruption level at 1.5 times the rated current, the system is designed to respond quickly to significant overloads while allowing for brief overloads that may occur during normal operation or start-up of equipment. Thus, this protection method balances the need for operational flexibility with safety.

In contrast, the other options do not accurately describe the functionality or characteristics of close excess-current protection. The first option suggests the protection does not operate, which contradicts its purpose. The third option inaccurately specifies a 2-hour requirement, misrepresenting the necessary response time. Lastly, stating that the protection operates only during low voltage conditions does not correspond to the general function of close excess-current protection, which is focused on overcurrent situations regardless of the voltage level.