PC Electrical System Design & Installation 2 — Questions and Answers
Question 1: When sizing a feeder for a commercial building with a calculated load of 180 amperes, what is the minimum conductor ampacity required per NEC Article 215?
- 150A
- 180A (Correct answer)
- 200A
- 225A
Correct answer: 180A
Feeder conductors must have an ampacity not less than the maximum load to be served, which is 180A per NEC 215.2(A)(1).
Question 2: Which NEC article governs the installation of electrical systems in hazardous (classified) locations?
- Article 300
- Article 500 (Correct answer)
- Article 400
- Article 600
Correct answer: Article 500
NEC Article 500 covers hazardous (classified) locations and defines the requirements for Class I, II, and III divisions.
Question 3: A 240V, single-phase motor nameplate shows 18A full-load current. What is the minimum branch circuit conductor ampacity required?
- 18A
- 20A
- 22.5A (Correct answer)
- 25A
Correct answer: 22.5A
Per NEC 430.22, branch circuit conductors for a single motor must have an ampacity of at least 125% of the motor's full-load current: 18A × 1.25 = 22.5A.
Question 4: When installing a panelboard in a bathroom of a dwelling unit, what does the NEC prohibit?
- Installing GFCI breakers
- Overcurrent protection above 15A
- Panelboard installation entirely (Correct answer)
- Use of copper conductors
Correct answer: Panelboard installation entirely
NEC 240.24(E) prohibits overcurrent devices from being located in bathrooms of dwelling units, guest rooms, or guest suites.
Question 5: What is the maximum voltage drop recommended by the NEC for branch circuits serving lighting and receptacle outlets in a commercial installation?
- 2%
- 3% (Correct answer)
- 5%
- 10%
Correct answer: 3%
NEC 210.19(A) informational note recommends that the maximum voltage drop on branch circuits not exceed 3% for best performance.
Question 6: In a 3-phase, 4-wire wye system with a measured line voltage of 208V, what is the phase voltage?
- 208V
- 120V (Correct answer)
- 240V
- 277V
Correct answer: 120V
In a 208V 3-phase wye system, phase voltage equals line voltage divided by √3 (208 ÷ 1.732 ≈ 120V).
Question 7: What type of grounding electrode is NOT permitted to be used as the sole grounding electrode under NEC 250.52?
- Concrete-encased electrode
- Ground ring
- Metal underground water pipe
- A single driven rod with resistance above 25 ohms (Correct answer)
Correct answer: A single driven rod with resistance above 25 ohms
A single rod electrode with a measured resistance above 25 ohms must be supplemented with an additional electrode per NEC 250.56.
PC Electrical System Design & Installation 2
When sizing a feeder for a commercial building with a calculated load of 180 amperes, what is the minimum conductor ampacity required per NEC Article 215?