Journeyman Electrician Exam (NEC)Special Occupancies, Equipment, and ConditionsEasy
An assembly hall with an occupancy of 500 people requires an emergency lighting system. The emergency system is supplied by a generator. According to NEC Article 700, what is the maximum permissible time for the emergency lighting to come on after the normal power supply fails?
- A30 seconds
- B5 seconds
- C10 seconds
- D1 second
Show answer & explanationAnswer & explanation
Correct answer: C. 10 seconds
NEC Section 700.12 states that emergency lighting systems must be arranged to provide illumination and power automatically within 10 seconds of the failure of the normal supply. This ensures immediate safety in places of assembly.
Why the other options are wrong
- A. This duration is too long for emergency lighting to provide adequate safety in an emergency.
- B. While a fast transfer, 5 seconds is not the general maximum allowed by NEC for emergency systems.
- D. This is a requirement for some very critical systems, but not the general requirement for emergency lighting in places of assembly.
Emergency System Transfer Time (General)
The maximum permissible time for an emergency power system to activate and supply power to designated loads after the normal power supply fails, as per NEC Article 700.
- Applies to general emergency systems (e.g., places of assembly).
- Ensures essential services during power outages.
- Mandated by NEC to be within 10 seconds.
Memory trick: Ten seconds is the time, for emergency power to shine.