Master Electrician Exam (NEC)Special Occupancies, Equipment, and ConditionsMedium
A master electrician is installing a new emergency system in a large assembly hall. The emergency system is intended to provide illumination and power for exit signs, emergency lighting, and essential communication systems upon failure of the normal power supply. What is the maximum permitted time delay for the emergency system to automatically come into full operation after the normal power failure?
- A30 seconds
- B60 seconds
- C5 seconds
- D10 seconds
Show answer & explanationAnswer & explanation
Correct answer: D. 10 seconds
NEC 700.12 requires that emergency lighting, emergency power, and emergency systems shall be arranged to provide full illumination and power to all required functions within 10 seconds of the normal power supply failure. This ensures prompt safety during emergencies.
Why the other options are wrong
- A. This delay is too long for emergency systems requiring immediate response.
- B. This delay is significantly too long for emergency systems.
- C. While faster is better, 5 seconds is not the maximum specified by NEC.
Emergency System Activation Time
The maximum permitted time delay for an emergency electrical system to automatically provide full power and illumination after a normal power failure.
- Governed by NEC 700.12
- Maximum 10-second delay.
- Ensures immediate safety in critical situations.
Memory trick: When power's out, emergency lights need to be on in a flash, within 10 seconds.