Journeyman Electrician Practice Test
Journeyman Electrician Electrical Theory & Calculations Practice Questions
Electrical Theory & Calculations makes up 5 of every 50 questions on a Tigertest Journeyman Electrician practice test. Here are 10 of the 20 questions on it, each with the answer and the reason.
Updated by the Tigertest team. Based on the 2023 National Electrical Code (NFPA 70) and standard electrical theory. Original questions; 50 per test, 70% to pass. State licensing law not included.
1. A 24-ohm resistive load is connected to 120 V. What current flows?
- A.2,880 A
- B.5 A
- C.0.2 A
- D.20 A
Answer: B. Ohm's law: I = E / R = 120 / 24 = 5 A. Dividing the wrong way gives 0.2, and multiplying gives 2,880, which is not a current.
2. A 1,500 W heater operates at 120 V. What current does it draw?
- A.15 A
- B.125 A
- C.6.25 A
- D.12.5 A
Answer: D. I = P / E = 1,500 / 120 = 12.5 A. The 6.25 A answer is the same heater at 240 V.
3. A 120 V, two-wire circuit of 12 AWG copper (6,530 cmil, K = 12.9) carries 16 A over 100 ft one way. About what is the voltage drop?
- A.About 6.3 V
- B.About 4.0 V
- C.About 3.2 V
- D.About 12.6 V
Answer: A. VD = 2 x K x I x L / CM = 2 x 12.9 x 16 x 100 / 6,530 = 6.3 V. Forgetting the 2 for the return path gives 3.2 V; 4.0 V is the result with 10 AWG.
4. Two 20-ohm resistors are connected in parallel. What is the total resistance?
- A.20 ohms
- B.5 ohms
- C.10 ohms
- D.40 ohms
Answer: C. Equal resistors in parallel divide: 20 / 2 = 10 ohms. Adding them (40 ohms) would be a series connection.
5. In a 208Y/120 V system, what is the voltage from a phase conductor to the neutral?
- A.240 V
- B.104 V
- C.120 V
- D.208 V
Answer: C. In a wye system the line-to-line voltage is 1.732 times the line-to-neutral voltage: 120 x 1.732 = 208 V. Phase to neutral is 120 V.
6. A balanced 30 kW three-phase resistive load is supplied at 208 V. About what is the line current?
- A.About 83 A
- B.About 48 A
- C.About 250 A
- D.About 144 A
Answer: A. Three-phase current is P / (E x 1.732) = 30,000 / (208 x 1.732) = 83.3 A. Leaving out the 1.732 gives 144 A.
7. On a 120/240 V three-wire circuit, line A carries 30 A and line B carries 20 A of 120 V load. What does the neutral carry?
- A.0 A
- B.50 A
- C.25 A
- D.10 A
Answer: D. On a single-phase three-wire system the neutral carries the difference between the two line currents: 30 - 20 = 10 A. It carries zero only when the loads are balanced.
8. In a balanced three-phase four-wire wye system with linear loads, the neutral current is:
- A.The sum of the phase currents
- B.Close to zero
- C.Equal to one phase current
- D.Three times one phase current
Answer: B. Balanced linear loads on a wye system cancel at the neutral, leaving almost no current. Nonlinear loads producing harmonics can change that, which is why some neutrals count as current-carrying.
9. On a 120/240 V four-wire delta system, the high leg measures about how much to ground?
- A.About 277 V
- B.About 208 V
- C.About 120 V
- D.About 240 V
Answer: B. The high leg of a center-tapped delta measures about 208 V to the grounded neutral (120 x 1.732). It must never feed 120 V loads.
10. A 2,000 W heater runs for 3 hours. How much energy does it use?
- A.5 kWh
- B.6,000 kWh
- C.0.67 kWh
- D.6 kWh
Answer: D. Energy = power x time = 2 kW x 3 h = 6 kWh. Writing 6,000 forgets to convert watts to kilowatts.
Practice all 20 electrical theory & calculations questions, and the rest of the 200-question bank, in the free Journeyman Electrician training sets. Questions you miss come back until you have mastered them.
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