Journeyman Electrician’s Exam Journeyman Electrician's Basic Formula 5

Question 1

What is the capacitive reactance (X_C) of a 100 μF capacitor at 60 Hz?

Accepted Answer

26.5 Ω

Answer

X_C = 1 / (2π × f × C) = 1 / (2π × 60 × 0.0001) ≈ 26.5 Ω.

Question 2

Inductive reactance (X_L) increases when frequency:

Accepted Answer

Increases

Answer

X_L = 2πfL, so inductive reactance is directly proportional to frequency.

Question 3

A 208V three-phase source supplies a balanced load drawing 30A per phase. What is the total three-phase apparent power?

Accepted Answer

18,720 VA

Answer

S = √3 × V_L × I_L = 1.732 × 208 × 30 ≈ 10,810 VA ≈ 10,816 VA.

Question 4

Using the power wheel, if you know resistance and voltage, power equals:

Accepted Answer

V² / R

Answer

P = V² / R is derived by substituting I = V/R into P = V × I.

Question 5

A feeder conductor has a resistance of 0.25Ω per wire and carries 80A. What is the total voltage drop for both conductors (one round trip)?

Accepted Answer

20 V

Answer

VD = I × R × 2 conductors = 80 × 0.25 × 2 = 40 V.

Journeyman Electrician’s Exam Practice Test