CME System Design and Installation 3 — Questions and Answers
Question 1: In designing a hospital critical branch circuit, what is the maximum transfer time required to restore power after normal power loss per NFPA 99?
- 5 seconds
- 10 seconds (Correct answer)
- 15 seconds
- 30 seconds
Correct answer: 10 seconds
NFPA 99 requires the critical branch of the essential electrical system to be restored within 10 seconds of normal power interruption.
Question 2: A master electrician is sizing conductors for a 208V, 3-phase motor with a full-load current of 40A. What is the minimum conductor ampacity required per NEC 430.22?
- 40A
- 46A
- 50A (Correct answer)
- 56A
Correct answer: 50A
NEC 430.22 requires motor branch circuit conductors to have an ampacity of not less than 125% of the motor full-load current: 40A × 1.25 = 50A.
Question 3: When installing a photovoltaic system, what is the maximum voltage of a PV source circuit permitted in a one- or two-family dwelling per NEC 690.7?
- 300V DC
- 480V DC
- 600V DC (Correct answer)
- 1000V DC
Correct answer: 600V DC
NEC 690.7(A) limits PV system voltage in one- and two-family dwellings to a maximum of 600V DC.
Question 4: What is the purpose of a system bonding jumper in a separately derived system per NEC 250.30?
- To connect the grounded conductor to the equipment grounding conductor at the source (Correct answer)
- To connect parallel conductors together
- To bond the neutral conductor to the transformer case
- To provide a low-impedance fault current path to utility ground
Correct answer: To connect the grounded conductor to the equipment grounding conductor at the source
The system bonding jumper connects the grounded conductor (neutral) to the equipment grounding conductor and to the enclosure at the source of a separately derived system.
Question 5: Per NEC 220.87, what is the permitted method for determining the existing load on a service for the purpose of adding new loads?
- Calculate 80% of the service rating
- Use actual maximum demand data for a 1-year period (Correct answer)
- Measure peak demand over any 30-day period and multiply by 1.25
- Calculate connected load using NEC demand factors
Correct answer: Use actual maximum demand data for a 1-year period
NEC 220.87 permits using actual maximum demand data recorded over a minimum 1-year period to determine the existing load for service upgrade calculations.
Question 6: In a commercial kitchen, what classification applies to the area within 18 inches of a cooking surface exhaust hood opening per NFPA 96 and NEC 500?
- Class I, Division 1
- Class I, Division 2
- Unclassified if proper ventilation is maintained (Correct answer)
- Class II, Division 1
Correct answer: Unclassified if proper ventilation is maintained
Properly ventilated commercial kitchen cooking areas are typically unclassified when NFPA 96 ventilation requirements are met, as the exhaust system removes flammable vapors.
Question 7: When designing a raceway system for a high-rise building, what is the maximum spacing for conduit supports on a vertical run of rigid metal conduit per NEC Table 344.30(B)(2)?
- Every 10 feet
- Every 15 feet
- Every 20 feet (Correct answer)
- Every 25 feet
Correct answer: Every 20 feet
NEC Table 344.30(B)(2) requires RMC supports at intervals not exceeding 20 feet for trade sizes 1 inch and above on straight runs.
CME System Design and Installation 3
In designing a hospital critical branch circuit, what is the maximum transfer time required to restore power after normal power loss per NFPA 99?