Journeyman Electrician's Basic Formula Flashcards
7 cards from real Journeyman Electrician’s Exam practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Journeyman Electrician's Basic Formula flashcards as text
A motor nameplate reads 5 HP and operates at 240V single-phase with 90% efficiency. Approximately how many amps does it draw?
Answer: 17.2 A
Input watts = (5 × 746) / 0.90 = 4,144 W; I = 4,144 / 240 ≈ 17.3 A.
Voltage drop in a conductor is calculated using which formula?
Answer: VD = I × R
Voltage drop (VD) = Current (I) × Resistance (R) of the conductor.
The NEC maximum allowable voltage drop for a branch circuit is:
Answer: 3%
NEC recommends no more than 3% voltage drop on a branch circuit (Article 210).
What is the cross-sectional area formula used when calculating minimum wire size for a given load?
Answer: A = ρ × L / R
Resistance R = ρL/A, rearranged gives A = ρ × L / R, where ρ is resistivity.
A 120V, 20A circuit feeds a continuous load. What is the maximum continuous load allowed by the NEC?
Answer: 1,920 W
Continuous load limit = 20 A × 0.80 × 120 V = 1,920 W (80% of circuit capacity).
What is the total impedance of a series AC circuit with 6Ω resistance and 8Ω inductive reactance?
Answer: 10 Ω
Z = √(R² + X_L²) = √(36 + 64) = √100 = 10 Ω.
Power factor is defined as the ratio of:
Answer: True power to apparent power
Power Factor (PF) = True Power (W) / Apparent Power (VA).