New York State Master Electrician Practice Exam

What must be able to be opened by hand in the event of a power supply failure?

1. A circuit breaker

2. A power-operated switch

3. A service disconnecting means

4. A fuse panel

The correct answer is: A service disconnecting means

In the event of a power supply failure, a service disconnecting means must be able to be opened by hand. This requirement is critical for safety and maintenance purposes. If the power goes out unexpectedly, especially in an emergency situation, having the ability to manually open the disconnect allows for safe access to the electrical system, enabling personnel to isolate the circuit and perform necessary checks or repairs without the risk of electrical shock or other hazards. While circuit breakers and fuse panels are indeed crucial for managing electrical circuits, they may not always be readily accessible for manual operation without tools. Power-operated switches, by their nature, rely on electrical power to operate, making them ineffective in a power failure scenario. Therefore, the manual operability of a service disconnecting means is an essential feature that ensures safety and compliance with electrical codes.