Journeyman Electrician’s Exam Journeyman Electrician's Basic Formula 4

Question 1

A motor nameplate reads 5 HP and operates at 240V single-phase with 90% efficiency. Approximately how many amps does it draw?

Accepted Answer

17.2 A

Answer

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?

Accepted Answer

VD = I × R

Answer

Voltage drop (VD) = Current (I) × Resistance (R) of the conductor.

Question 3

The NEC maximum allowable voltage drop for a branch circuit is:

Accepted Answer

3%

Answer

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?

Accepted Answer

A = ρ × L / R

Answer

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?

Accepted Answer

1,920 W

Answer

Continuous load limit = 20 A × 0.80 × 120 V = 1,920 W (80% of circuit capacity).

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