E2 Systems and Equipment 2 — Questions and Answers
Question 1: According to the NEC, what is the minimum clearance required above a switchboard in a commercial installation?
- 3 feet
- 6 feet (Correct answer)
- 6.5 feet
- 8 feet
Correct answer: 6 feet
NEC 110.26(A)(1) requires a minimum of 6 feet of headroom above electrical equipment such as switchboards.
Question 2: A commercial building's emergency lighting system is required to provide illumination for at least how long upon loss of normal power?
- 30 minutes
- 60 minutes
- 90 minutes (Correct answer)
- 120 minutes
Correct answer: 90 minutes
NEC 700.12 requires emergency lighting systems to provide at least 90 minutes of operation upon normal power failure.
Question 3: When inspecting a variable frequency drive (VFD) installation, which conductor issue is most critical to verify?
- Wire insulation color
- Conductor ampacity derating for harmonic heating (Correct answer)
- Use of aluminum conductors only
- Minimum 10 AWG branch circuit
Correct answer: Conductor ampacity derating for harmonic heating
VFDs produce harmonics that cause additional heating in conductors, requiring ampacity derating per NEC 310.15(A)(2).
Question 4: Under the NEC, a motor controller must be capable of interrupting the stalled-rotor current of the motor it controls. This rating is known as the:
- Full load current (FLC)
- Locked rotor current (LRC) (Correct answer)
- Service factor amperage
- Running overload rating
Correct answer: Locked rotor current (LRC)
Motor controllers must be rated for locked rotor current (LRC), which is the maximum current drawn when the motor shaft is stalled.
Question 5: In a commercial kitchen, a dishwasher is hardwired to a 20-ampere, 120-volt circuit. The NEC requires this circuit to be protected by a:
- Standard GFCI breaker (Correct answer)
- AFCI breaker
- GFCI with 4mA trip threshold
- Standard overcurrent device only
Correct answer: Standard GFCI breaker
NEC 210.8(B) requires GFCI protection for commercial kitchen equipment in areas where water is present.
Question 6: What does the NEC require for grounding electrode conductors at a commercial service entrance that uses a metal water pipe as a grounding electrode?
- The conductor must be at least 4 AWG copper
- A supplemental electrode must also be installed (Correct answer)
- The pipe must be bonded with a 6 AWG conductor only
- No supplemental electrode is needed if the pipe is 3/4 inch or larger
Correct answer: A supplemental electrode must also be installed
NEC 250.53(D)(2) requires a supplemental grounding electrode when a metal water pipe is used as a grounding electrode.
Question 7: A rooftop HVAC unit on a commercial building is served by a disconnect switch mounted on the unit. The NEC requires this disconnect to be:
- Lockable in the open position (Correct answer)
- Rated at 200% of the motor FLA
- Located inside the unit's electrical compartment
- A fused safety switch only
Correct answer: Lockable in the open position
NEC 430.102(B) and 440.14 require the disconnecting means for HVAC equipment to be lockable in the open (off) position.
E2 Systems and Equipment 2
According to the NEC, what is the minimum clearance required above a switchboard in a commercial installation?