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Question 1. What is the unit of electrical resistance? A) Ampere B) Ohm C) Volt D) Watt Answer: B Explanation: The ohm is the standard unit of electrical resistance, representing the opposition to current flow in a circuit. Question 2. According to Ohm’s Law, if voltage increases and resistance remains constant, what happens to the current? A) Decreases B) Increases C) Stays the same D) Drops to zero Answer: B Explanation: Ohm’s Law (I=V/R) shows that current is directly proportional to voltage when resistance is constant. Question 3. Which formula correctly calculates electrical power in a DC circuit? A) P = I/R
B) P = V/I
C) P = V × I
D) P = V^2 × R
Answer: C Explanation: Power (P) is equal to the product of voltage (V) and current (I). Question 4. In a parallel circuit, how is the total resistance calculated? A) Add all resistances B) Multiply all resistances C) Reciprocal of the sum of reciprocals D) Subtract the smallest from the largest resistance Answer: C Explanation: Total resistance in parallel is found using 1/Rt = 1/R1 + 1/R2 + 1/R3, etc. Question 5. Which type of current reverses direction periodically? A) Direct Current B) Alternating Current C) Pulsating DC D) Static Current
Question 8. What is the main function of a transformer? A) Convert AC to DC B) Change voltage levels C) Measure current D) Store electrical energy Answer: B Explanation: Transformers change AC voltage levels up or down. Question 9. Which of the following is a conductive material? A) Glass B) Rubber C) Copper D) Porcelain Answer: C Explanation: Copper is an excellent conductor of electricity; the others are insulators. Question 10. If two 10-ohm resistors are connected in series, what is the total resistance? A) 5 ohms B) 10 ohms
C) 20 ohms D) 100 ohms Answer: C Explanation: In series, resistances add directly; 10 + 10 = 20 ohms. Question 11. What is the purpose of grounding an electrical system? A) Improve efficiency B) Provide a path for fault current C) Increase current D) Reduce voltage Answer: B Explanation: Grounding provides a safe path for fault current to prevent electric shock and equipment damage. Question 12. Which NEC article covers grounding and bonding? A) Article 100 B) Article 250 C) Article 300 D) Article 400 Answer: B
Question 15. A 20-ampere branch circuit in a dwelling unit must use conductors of at least what size? A) 18 AWG B) 14 AWG C) 12 AWG D) 10 AWG Answer: C Explanation: NEC Table 310.16 requires a minimum of 12 AWG copper for 20-amp circuits. Question 16. What is the maximum continuous load permitted on a 100-ampere circuit breaker? A) 100 amps B) 80 amps C) 90 amps D) 70 amps Answer: B Explanation: NEC 210.20(A) requires that continuous loads not exceed 80% of the breaker rating. Question 17. Which device is used to protect a circuit from overload?
A) Transformer B) Switch C) Circuit breaker D) Receptacle Answer: C Explanation: Circuit breakers interrupt current flow when an overload occurs. Question 18. What is the minimum working space depth required in front of electrical equipment rated 600V or less? A) 24 inches B) 36 inches C) 42 inches D) 48 inches Answer: B Explanation: NEC 110.26(A)(1) requires at least 36 inches of working space depth. Question 19. When calculating box fill, how many conductors are counted for each device (switch or receptacle) in the box? A) None B) One C) Two
Explanation: Bonding connects all metallic parts to ensure there are no potential differences that could cause electric shock. Question 22. In a three-phase system, what is the phase-to-phase voltage if the phase-to-neutral voltage is 120V? A) 120V B) 208V C) 240V D) 277V Answer: B Explanation: Phase-to-phase voltage in a 120V system is 120V × √3 ≈ 208V. Question 23. What is the allowable ampacity of a single 8 AWG copper conductor with THHN insulation in a raceway at 30°C ambient temperature? A) 40 amps B) 50 amps C) 55 amps D) 60 amps Answer: C Explanation: NEC Table 310.16 lists 8 AWG THHN copper at 55 amps.
Question 24. Which NEC article provides rules for installing flexible cords and cables? A) Article 210 B) Article 240 C) Article 400 D) Article 500 Answer: C Explanation: Article 400 covers flexible cords and cables. Question 25. What is the minimum service entrance conductor size for a 200-amp residential service using copper? A) 1 AWG B) 2/0 AWG C) 4 AWG D) 3/0 AWG Answer: B Explanation: NEC Table 310.12 requires at least 2/0 AWG copper for a 200-amp service. Question 26. What is the maximum number of 12 AWG conductors permitted in a 4 - inch square, 2-1/8 inch deep metal box?
B) 10 feet C) 12 feet D) 16 feet Answer: B Explanation: NEC 230.24(B) requires a minimum of 10 feet above driveways. Question 29. What does GFCI stand for? A) Ground Fault Circuit Interrupter B) General Fault Current Indicator C) Grounded Fuse Circuit D) General Frequency Circuit Interrupter Answer: A Explanation: GFCI devices protect against ground faults by interrupting the circuit. Question 30. Which of the following must be grounded in all installations? A) Non-metallic conduit B) Metallic conduit C) PVC boxes D) Fiber optic cables Answer: B
Explanation: Metallic conduit must be grounded to ensure safety. Question 31. The term “ampacity” refers to: A) The voltage rating of a conductor B) The maximum current a conductor can carry safely C) The resistance of a conductor D) The power rating of a device Answer: B Explanation: Ampacity is the safe current-carrying capacity of a conductor. Question 32. A load of 2400W is connected to a 120V circuit. What is the current? A) 10A B) 15A C) 20A D) 25A Answer: D Explanation: I = P/V; 2400W/120V = 20A. Question 33. Which NEC section covers requirements for arc-fault circuit interrupters (AFCIs)?
D) Thermomagnetic breaker Answer: C Explanation: Switches do not provide overcurrent protection. Question 36. Which of the following formulas is used to calculate voltage drop? A) VD = IR B) VD = 2 × K × I × D / CM C) VD = P/I D) VD = V/R Answer: B Explanation: The formula for voltage drop includes the distance, conductor size, and current. Question 37. What is the maximum allowable voltage drop for a feeder or branch circuit according to good practice? A) 1% B) 3% C) 5% D) 10% Answer: B
Explanation: While the NEC does not mandate, it recommends a maximum of 3% voltage drop. Question 38. In a three-phase system, how much power (in kW) is delivered with a line voltage of 480V, current of 50A, and power factor of 0.8? A) 19.2 kW B) 33.2 kW C) 39.8 kW D) 66.5 kW Answer: B Explanation: P = √3 × V × I × PF = 1.732 × 480 × 50 × 0.8 = 33,177 W ≈ 33.2 kW. Question 39. Which of the following conductors is NOT permitted for use as a grounding electrode conductor? A) Copper B) Aluminum C) Steel D) Silver Answer: D Explanation: Silver is not used as a grounding electrode conductor.
C) Ammeter D) Wattmeter Answer: C Explanation: Ammeters measure current. Question 43. What is the minimum size EMT required for three 8 AWG THHN conductors? A) 1/2 inch B) 3/4 inch C) 1 inch D) 1-1/4 inch Answer: B Explanation: NEC Chapter 9, Table 1 and Table 5 allow three 8 AWG in a 3/4 inch EMT. Question 44. A 15A, 120V circuit supplies ten duplex receptacles. What is the maximum load permitted on any single receptacle? A) 1.5A B) 7.5A C) 12A D) 15A
Answer: B Explanation: NEC 210.21(B)(2) allows 80% of the circuit for a single receptacle on a multioutlet circuit. Question 45. What is the required minimum height for a residential service meter above finished grade? A) 2 feet B) 3 feet C) 4 feet D) 5 feet Answer: C Explanation: Most utilities and codes require 4 to 6 feet above grade for accessibility. Question 46. Which type of transformer has only one winding that acts as both the primary and secondary? A) Isolation transformer B) Step-up transformer C) Autotransformer D) Buck-boost transformer Answer: C
