Journeyman Electrician’s Exam Journeyman Electrician's Basic Formula 4 — Questions and Answers
Question 1: A motor nameplate reads 5 HP and operates at 240V single-phase with 90% efficiency. Approximately how many amps does it draw?
- 15.5 A
- 17.2 A (Correct answer)
- 20.9 A
- 23.2 A
Correct answer: 17.2 A
Input watts = (5 × 746) / 0.90 = 4,144 W; I = 4,144 / 240 ≈ 17.3 A.
Question 2: Voltage drop in a conductor is calculated using which formula?
- VD = I / R
- VD = I × R (Correct answer)
- VD = V / I
- VD = R / I
Correct answer: VD = I × R
Voltage drop (VD) = Current (I) × Resistance (R) of the conductor.
Question 3: The NEC maximum allowable voltage drop for a branch circuit is:
- 5%
- 3% (Correct answer)
- 10%
- 1%
Correct answer: 3%
NEC recommends no more than 3% voltage drop on a branch circuit (Article 210).
Question 4: What is the cross-sectional area formula used when calculating minimum wire size for a given load?
- A = ρL / R
- A = ρ × L / R (Correct answer)
- A = R × L / ρ
- A = V × L / I
Correct answer: A = ρ × L / R
Resistance R = ρL/A, rearranged gives A = ρ × L / R, where ρ is resistivity.
Question 5: A 120V, 20A circuit feeds a continuous load. What is the maximum continuous load allowed by the NEC?
- 2,400 W
- 1,920 W (Correct answer)
- 1,800 W
- 2,000 W
Correct answer: 1,920 W
Continuous load limit = 20 A × 0.80 × 120 V = 1,920 W (80% of circuit capacity).
Question 6: What is the total impedance of a series AC circuit with 6Ω resistance and 8Ω inductive reactance?
- 14 Ω
- 10 Ω (Correct answer)
- 48 Ω
- 2 Ω
Correct answer: 10 Ω
Z = √(R² + X_L²) = √(36 + 64) = √100 = 10 Ω.
Question 7: Power factor is defined as the ratio of:
- Apparent power to reactive power
- True power to apparent power (Correct answer)
- Reactive power to true power
- Voltage to current
Correct answer: True power to apparent power
Power Factor (PF) = True Power (W) / Apparent Power (VA).
Journeyman Electrician’s Exam Journeyman Electrician's Basic Formula 4
A motor nameplate reads 5 HP and operates at 240V single-phase with 90% efficiency.
Approximately how many amps does it draw?