Licensed Electrical Contractor Electrical System Design & Installation 2 — Questions and Answers
Question 1: When sizing conductors for a continuous load, the conductor ampacity must be at least what percentage of the load's ampere rating per NEC 210.19?
- 100%
- 115%
- 125% (Correct answer)
- 80%
Correct answer: 125%
NEC 210.19(A)(1) requires conductors for continuous loads to be sized at 125% of the continuous load ampere rating.
Question 2: Which conductor material requires anti-oxidant compound when terminating at devices or equipment?
- Copper
- Aluminum (Correct answer)
- Copper-clad aluminum
- Tinned copper
Correct answer: Aluminum
Aluminum conductors oxidize at connections, so anti-oxidant compound is required to ensure a reliable, low-resistance termination.
Question 3: A 240V single-phase motor draws 28 amperes at full load. The minimum branch circuit conductor size using 75°C copper wire (THWN) is:
- 10 AWG
- 8 AWG (Correct answer)
- 6 AWG
- 12 AWG
Correct answer: 8 AWG
Motor branch circuits must be sized at 125% of FLA: 28A × 1.25 = 35A, requiring 8 AWG THWN copper rated at 50A.
Question 4: Which NEC article governs the installation of electrical systems in hazardous (classified) locations?
- Article 410
- Article 500 (Correct answer)
- Article 600
- Article 700
Correct answer: Article 500
NEC Article 500 covers hazardous (classified) locations, defining Class I, II, and III divisions and zones.
Question 5: In a delta-wye transformer installation, which winding configuration provides a neutral conductor on the secondary side?
- Delta primary, delta secondary
- Wye primary, delta secondary
- Delta primary, wye secondary (Correct answer)
- Wye primary, wye secondary
Correct answer: Delta primary, wye secondary
A delta-wye configuration provides a neutral on the wye secondary, enabling 3-phase 4-wire distribution systems.
Question 6: What is the maximum distance a disconnecting means can be located from the point of entrance for a service in a building?
- 10 feet
- The first point of entrance to the building (Correct answer)
- At the nearest accessible location
- No more than 20 feet inside the building
Correct answer: The first point of entrance to the building
NEC 230.70 requires the service disconnecting means to be installed at the nearest point of entrance of the service conductors inside or outside the building.
Question 7: For a 3-phase, 4-wire wye system rated 208Y/120V, what is the voltage measured between any phase conductor and the neutral?
- 208V
- 120V (Correct answer)
- 240V
- 277V
Correct answer: 120V
In a 208Y/120V system, 120V is the phase-to-neutral voltage and 208V is the phase-to-phase voltage.
