E2 Emergency and Standby Systems 2 — Questions and Answers
Question 1: Under NEC Article 700, how soon must an emergency system automatically restore power after normal supply fails?
- Within 1 second
- Within 10 seconds (Correct answer)
- Within 30 seconds
- Within 60 seconds
Correct answer: Within 10 seconds
NEC 700.12 requires emergency systems to supply power within 10 seconds of normal power failure.
Question 2: Which NEC article governs Legally Required Standby Systems in commercial occupancies?
- Article 700
- Article 701 (Correct answer)
- Article 702
- Article 708
Correct answer: Article 701
NEC Article 701 covers Legally Required Standby Systems, which differ from emergency systems covered in Article 700.
Question 3: An automatic transfer switch (ATS) for an emergency system must be listed and be capable of withstanding:
- Available fault current at the point of installation (Correct answer)
- Only the rated load current
- 125% of full load current
- The utility transformer rating
Correct answer: Available fault current at the point of installation
Per NEC 700.5(A), transfer switches must be suitable for the available fault current at the point where they are installed.
Question 4: Emergency system branch circuits must be kept entirely independent of other wiring with a limited exception for:
- Transfer switch enclosures only
- Common junction boxes shared with normal wiring
- Transfer equipment and exit lighting enclosures listed for the purpose (Correct answer)
- Conduit runs that share a common raceway
Correct answer: Transfer equipment and exit lighting enclosures listed for the purpose
NEC 700.10(B) permits emergency wiring to share enclosures only at transfer equipment and exit lighting fixtures listed for the purpose.
Question 5: A generator used as the alternate power source for an emergency system must be provided with selective coordination from the emergency panel to the transfer switch for fault currents lasting:
- 0.1 second and longer (Correct answer)
- 0.5 second and longer
- 1 second and longer
- 10 seconds and longer
Correct answer: 0.1 second and longer
NEC 700.32 requires selective coordination of overcurrent devices for fault durations of 0.1 second and longer.
Question 6: Where must the location of emergency system components be indicated in a commercial building?
- On exterior signage only
- In the certificate of occupancy
- On a drawing posted at the main service location (Correct answer)
- In the building's maintenance manual only
Correct answer: On a drawing posted at the main service location
NEC 700.10(A) requires a sign at the main service showing the type, capacity, and location of all on-site emergency power sources.
Question 7: Emergency lighting circuits supplying exit signs must be capable of operating for a minimum of:
- 30 minutes on battery backup
- 60 minutes on battery backup
- 90 minutes on battery backup (Correct answer)
- 120 minutes on battery backup
Correct answer: 90 minutes on battery backup
NFPA 101 and NEC 700 require emergency lighting to be capable of operating for a minimum of 90 minutes after loss of normal power.
E2 Emergency and Standby Systems 2
Under NEC Article 700, how soon must an emergency system automatically restore power after normal supply fails?