Licensed Electrical Contractor Code, Theory, and Calculations 3 — Questions and Answers
Question 1: What NEC section governs the installation of conductors in raceways, and what is the maximum fill percentage for a single conductor in a conduit?
- NEC 358.22 — 53%
- NEC 344.22 — 31%
- NEC 310.15 — 40%
- NEC 300.17 — 53% (Correct answer)
Correct answer: NEC 300.17 — 53%
NEC 300.17 references Chapter 9 Table 1, which allows 53% fill for a single conductor in a conduit.
Question 2: What is the reactance of a 60 Hz circuit with an inductance of 0.5 H?
- 188.5 Ω (Correct answer)
- 94.2 Ω
- 376.9 Ω
- 30 Ω
Correct answer: 188.5 Ω
Inductive reactance XL = 2πfL = 2π × 60 × 0.5 ≈ 188.5 Ω.
Question 3: Under NEC 210.8(A), GFCI protection is required for all 125 V, 15 A and 20 A receptacles in which residential location?
- All outdoor locations (Correct answer)
- Living room only
- Bedrooms only
- Attic storage areas only
Correct answer: All outdoor locations
NEC 210.8(A) requires GFCI protection for all 125 V, 15 A and 20 A receptacles installed in outdoor locations of dwelling units.
Question 4: A 480 V, 3-phase, 4-wire wye system has a line-to-neutral voltage of approximately:
- 277 V (Correct answer)
- 240 V
- 208 V
- 347 V
Correct answer: 277 V
Line-to-neutral voltage = line voltage ÷ √3 = 480 ÷ 1.732 ≈ 277 V.
Question 5: Per NEC 250.122, the minimum size equipment grounding conductor (EGC) for a circuit protected by a 200 A overcurrent device is:
- 6 AWG copper (Correct answer)
- 4 AWG copper
- 8 AWG copper
- 2 AWG copper
Correct answer: 6 AWG copper
NEC Table 250.122 specifies a minimum 6 AWG copper EGC for circuits protected by overcurrent devices up to 200 A.
Question 6: In a capacitive AC circuit, the current:
- Leads the voltage by 90° (Correct answer)
- Lags the voltage by 90°
- Is in phase with voltage
- Leads the voltage by 45°
Correct answer: Leads the voltage by 90°
In a purely capacitive circuit, current leads voltage by 90° because the capacitor charges before the voltage peaks.
Question 7: NEC 408.36 requires panelboards supplied by a 4-wire delta system to be labeled to indicate the:
- High-leg (wild leg) conductor and its voltage to ground (Correct answer)
- Total panel ampacity rating
- Number of branch circuits permitted
- Grounding conductor size
Correct answer: High-leg (wild leg) conductor and its voltage to ground
NEC 408.36 requires the high-leg (wild leg) of a 4-wire delta system to be durably marked at the panelboard to indicate its higher voltage to ground (typically 208 V).
Licensed Electrical Contractor Code, Theory, and Calculations 3
What NEC section governs the installation of conductors in raceways, and what is the maximum fill percentage for a single conductor in a conduit?