CEI Commercial & Industrial Systems 2 — Questions and Answers
Question 1: What is the minimum headroom clearance required in front of electrical equipment rated 600V or less in a commercial occupancy per NEC 110.26?
- 2 ft 6 in
- 3 ft 0 in (Correct answer)
- 3 ft 6 in
- 4 ft 0 in
Correct answer: 3 ft 0 in
NEC 110.26(A)(1) requires a minimum working clearance of 3 ft (900 mm) for equipment rated 600V or less.
Question 2: A 480V, 3-phase industrial motor has a full-load current of 40A. What is the maximum allowable branch-circuit short-circuit and ground-fault protection for an inverse-time breaker?
- 100A
- 125A
- 150A (Correct answer)
- 200A
Correct answer: 150A
NEC 430.52 and Table 430.52 permit inverse-time breakers at 250% of FLC for motors; 40A × 250% = 100A, but the next standard size up to 150A is permitted when 100A does not allow starting.
Question 3: Which NEC article governs the installation of busways (bus ducts) in commercial and industrial facilities?
- Article 362
- Article 368 (Correct answer)
- Article 372
- Article 376
Correct answer: Article 368
NEC Article 368 covers busways, including their installation, support, and use in commercial and industrial applications.
Question 4: In an industrial facility, a 480/277V panelboard supplies lighting circuits. What is the maximum voltage-to-ground permitted for lighting circuits in commercial occupancies?
- 120V
- 208V
- 277V (Correct answer)
- 480V
Correct answer: 277V
NEC 210.6(D) permits lighting circuits up to 277V to ground in commercial and industrial occupancies when installed in approved luminaires.
Question 5: What type of grounding electrode is required to be used when a building has a metal water pipe that is at least 10 ft of the pipe in contact with the earth?
- Ground ring
- Rod electrode
- Metal water piping system (Correct answer)
- Concrete-encased electrode
Correct answer: Metal water piping system
NEC 250.52(A)(1) requires the metal underground water piping system with at least 10 ft in contact with earth to be used as a grounding electrode.
Question 6: An industrial control panel contains a transformer that steps 480V down to 120V for control circuits. What is the maximum overcurrent protection permitted on the 120V secondary if the secondary conductors are 12 AWG copper?
- 15A
- 20A (Correct answer)
- 25A
- 30A
Correct answer: 20A
NEC 240.4(D) limits 12 AWG copper conductors to a maximum of 20A overcurrent protection.
Question 7: Per NEC 230.71, what is the maximum number of service disconnecting means permitted for a single set of service entrance conductors supplying a commercial building?
- 3
- 4
- 6 (Correct answer)
- 8
Correct answer: 6
NEC 230.71(A) limits the number of service disconnecting means to a maximum of six for a single set of service-entrance conductors.
CEI Commercial & Industrial Systems 2
What is the minimum headroom clearance required in front of electrical equipment rated 600V or less in a commercial occupancy per NEC 110.26?