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531SD Contractor Ultimate Exam
Question 1. What is the correct expression of Ohm’s Law? A) V = I ÷ R B) I = V × R C) V = I × R D) R = V ÷ I Answer: C Explanation: Ohm’s Law states that voltage (V) equals current (I) multiplied by resistance (R). Question 2. If a circuit has a voltage of 120 V and a current of 10 A, what is the power consumed? A) 12 W B) 120 W C) 1,200 W D) 12,000 W Answer: C Explanation: Power (P) = V × I = 120 V × 10 A = 1,200 W. Question 3. According to NEC Article 100, the term “grounded conductor” refers to which of the following? A) The neutral conductor that is intentionally connected to earth at the service. B) Any equipment grounding conductor. C) The ungrounded (hot) conductor. D) The grounding electrode conductor. Answer: A Explanation: The grounded conductor is the neutral that is bonded to the grounding electrode system at the service. Question 4. When reading a single-line diagram, a solid diamond symbol represents which component? A) Switch
531SD Contractor Ultimate Exam
B) Transformer C) Motor D) Panelboard Answer: B Explanation: In NEC single-line symbols, a solid diamond denotes a transformer. Question 5. A residential service requires a minimum of 200 A. Which NEC demand factor should be applied to calculate the feeder size for a dwelling with 30 kW of non-continuous load? A) 100 % B) 80 % C) 75 % D) 40 % Answer: B Explanation: NEC Table 220.42 permits 100 % of the first 10 kW and 40 % of the remainder; the overall demand factor for a typical dwelling is 80 % for the calculated load. Question 6. What is the required size of the grounding electrode conductor (GEC) for a 200 A service with copper conductors? A) 6 AWG copper B) 8 AWG copper C) 4 AWG copper D) 2 AWG copper Answer: C Explanation: NEC Table 250.66 requires a 4 AWG copper GEC for a 200 A service. Question 7. Which of the following is an acceptable grounding electrode? A) A metal water pipe not bonded within 5 ft of the service. B) A concrete-encased electrode (Ufer) at least 20 ft of #4 rebar. C) A wooden pole driven into the earth.
531SD Contractor Ultimate Exam
Explanation: 3 % of 240 V = 7.2 V; the feeder voltage drop must not exceed this value. Question 11. What is the minimum size of equipment grounding conductor (EGC) for a 20 A branch circuit protected by a 20 A breaker, using copper conductors? A) 12 AWG B) 14 AWG C) 10 AWG D) 8 AWG Answer: B Explanation: NEC Table 250.122 specifies 14 AWG copper for a 20 A overcurrent device. Question 12. Which insulation type is permitted for wet locations and has a temperature rating of 90 °C? A) THHN B) XHHW- 2 C) NM-B D) UF-B Answer: B Explanation: XHHW-2 is rated for 90 °C and approved for wet locations. Question 13. A conduit run contains three #6 AWG THHN conductors and a #10 AWG EGC. What is the minimum conduit size required for 40 % fill? A) 1/2 in. EMT B) 3/4 in. EMT C) 1 in. EMT D) 1 1/4 in. EMT Answer: B Explanation: Each #6 THHN occupies 0.050 in², #10 EGC 0.021 in²; total 0.171 in². 40 % of 3/4 in. EMT (0.533 in²) = 0.213 in², which is sufficient.
531SD Contractor Ultimate Exam
Question 14. Which NEC article specifies the requirements for air-conditioning and refrigeration equipment? A) Article 430 B) Article 440 C) Article 460 D) Article 422 Answer: B Explanation: Article 440 governs the installation of air-conditioning and refrigerating equipment. Question 15. **A 3-phase motor has a full-load current of 25 A and is protected by a circuit breaker. What is the maximum rating of the breaker allowed by NEC 430.32? ** A) 35 A B) 40 A C) 45 A D) 50 A Answer: B Explanation: NEC 430.32 permits a breaker up to 250 % of motor FLC: 1.25 × 25 A = 31.25 A; the next standard size is 35 A, but for non-inverse time breakers the max is 250 % → 62.5 A, however for inverse-time breakers 125 % → 31.25 A. The closest standard inverse-time size is 35 A, but the code allows 40 A for certain applications. The safest answer is 35 A. (Correct answer: A) Question 16. Which of the following devices must be GFCI-protected in a residential garage according to NEC 210.8(A)(2)? A) All receptacles B) Only receptacles supplying 120 V, 15- or 20-A circuits C) Only receptacles for power tools D) No receptacles, only lighting fixtures Answer: B
531SD Contractor Ultimate Exam
Explanation: NEC 690.13 requires a disconnect sized at not less than the maximum current of the array; 12 kW ÷ 600 V = 20 A, rounded up to the next standard size → 20 A. However a 30 A disconnect is commonly used to allow for future expansion. (Correct answer: B) Question 20. Which NEC article governs the installation of emergency power systems, including automatic transfer switches? A) Article 700 B) Article 710 C) Article 720 D) Article 730 Answer: A Explanation: Article 700 covers emergency systems, including ATS and standby power. Question 21. In a wye-connected 120/208 V system, what is the voltage between any two phases? A) 120 V B) 208 V C) 240 V D) 277 V Answer: B Explanation: The line-to-line voltage in a 120/208 V wye system is 208 V. Question 22. What is the minimum clearance required between a service entrance conductor and a grounded metal water pipe that is not used as a grounding electrode? A) 1 ft B) 6 in. C) 12 in. D) No clearance required if bonded. Answer: B
531SD Contractor Ultimate Exam
Explanation: NEC 250.68(A) requires a minimum of 6 in. separation unless the pipe is used as a grounding electrode. Question 23. A 120/240 V single-phase feeder supplies a 30 A branch circuit for an electric range. Which conductor size is required for the feeder if the conduit fill is limited to 40 %? A) 6 AWG copper B) 4 AWG copper C) 2 AWG copper D) 8 AWG copper Answer: B Explanation: A 30 A load requires at least 4 AWG copper per NEC Table 310.15(B) (16) for 75 °C rating; conduit fill at 40 % permits this size. Question 24. Which device is required to protect a 150-A service panel from overcurrent according to NEC 230.71? A) A 150-A main breaker located in the panel. B) A 200-A fuse at the service disconnect. C) A 125-A breaker upstream of the service. D) No device is required if the utility provides protection. Answer: A Explanation: NEC 230.71 requires a disconnecting means at the service, typically a main breaker sized for the service rating. Question 25. When installing a grounding electrode conductor (GEC) in a raceway, what is the maximum length of the raceway allowed without a bonding jumper? A) 6 ft B) 10 ft C) 12 ft D) 18 ft Answer: B
531SD Contractor Ultimate Exam
Question 29. A lighting circuit in a commercial office is required to be supplied by a 20 A branch circuit. What is the minimum number of receptacles allowed on this circuit per NEC 210.52(C)(2)? A) 2 B) 4 C) 6 D) No limit, as long as the load does not exceed 80 % of the circuit rating. Answer: D Explanation: NEC does not limit the number of receptacles on a lighting circuit; the total load must not exceed 80 % of the circuit rating for continuous loads. Question 30. What is the maximum allowable ampacity for a 3-wire 12/2 NM-B cable protected by a 20 A breaker? A) 15 A B) 20 A C) 25 A D) 30 A Answer: B Explanation: NM-B 12 AWG is rated for 20 A at 60 °C, matching the breaker size. Question 31. Which of the following is the correct method to size the neutral conductor for a 120/240 V, single-phase, 3-wire feeder supplying only continuous loads? A) Same size as the ungrounded conductors. B) 80 % of the ungrounded conductor size. C) 50 % of the ungrounded conductor size. D) No neutral required. Answer: A Explanation: For a feeder supplying only continuous loads, the neutral must be sized equal to the ungrounded conductors unless a load calculation shows a smaller size is permissible.
531SD Contractor Ultimate Exam
Question 32. In a hazardous Class I, Division 2 location, which type of wiring method is permitted for power circuits? A) Non-metallic sheathed cable (NM). B) Rigid metal conduit (RMC). C) Flexible metal conduit (FMC). D) All of the above. Answer: B Explanation: RMC is allowed in Class I, Division 2; NM is not permitted in hazardous locations. Question 33. Which NEC article defines the requirements for raceway and cable fill calculations? A) Article 300 B) Article 310 C) Article 314 D) Article 376 Answer: C Explanation: Article 314 covers boxes, conduit, and raceway fill calculations. Question 34. A motor starter is rated for 30 A and uses a 125 % overload setting. What is the maximum overload current before the device trips? A) 30 A B) 37.5 A C) 45 A D) 60 A Answer: B Explanation: 125 % of 30 A = 37.5 A; the overload will trip at this current. Question 35. Which of the following is required for a fire alarm system’s wiring in a commercial building?
531SD Contractor Ultimate Exam
C) Article 700 D) Article 710 Answer: D Explanation: Article 710 covers standby and emergency power systems, including generators and ATS. Question 39. A 15-kW, 240 V electric water heater is to be installed on a dedicated circuit. What is the minimum breaker size required? A) 30 A B) 40 A C) 50 A D) 60 A Answer: B Explanation: Current = 15,000 W ÷ 240 V = 62.5 A; the breaker must be sized at 125 % of continuous load → 78 A, but the next standard size is 80 A. However NEC permits 125 % for continuous loads; the correct answer is 80 A. (Correct answer: D) Question 40. Which of the following is the correct method to terminate a grounding electrode conductor to a concrete-encased electrode? A) Directly clamp to the rebar. B) Use a listed listed grounding electrode clamp. C) Tie with a wire-nut. D) No connection needed; the rebar is already grounded. Answer: B Explanation: NEC requires a listed grounding electrode clamp to connect the GEC to the rebar. Question 41. In a three-phase, 4-wire wye system, what is the purpose of the neutral conductor? A) To carry unbalanced load current back to the source. B) To provide a path for fault currents only.
531SD Contractor Ultimate Exam
C) To act as a protective earth. D) To reduce line voltage. Answer: A Explanation: The neutral carries the vector sum of the unbalanced phase currents. Question 42. **Which NEC article specifies the requirements for box fill calculations? ** A) Article 300 B) Article 314 C) Article 376 D) Article 408 Answer: B Explanation: Box fill is addressed in Article 314. Question 43. A conduit system is installed in a building with a temperature rating of 60 °C. Which conductor insulation is permissible for this environment? A) THHN (90 °C) B) NM-B (60 °C) C) UF-B (60 °C) D) All of the above. Answer: D Explanation: Conductors may be used at the temperature rating of the enclosure; all listed options are permitted at 60 °C. Question 44. What is the required GFCI protection for a receptacle that supplies a pool pump in a residential pool area? A) No GFCI required. B) GFCI protected only if the pump is > 1 HP. C) GFCI protection required per NEC 680.22(A)(1). D) Only a GFCI breaker is acceptable, not a receptacle. Answer: C
531SD Contractor Ultimate Exam
Question 48. A commercial building has a fire alarm circuit that must be independent of other power circuits. Which wiring method is required? A) NM cable in the same conduit as power. B) Separate raceway dedicated to fire alarm. C) Shared conduit with power conductors. D) No special requirement. Answer: B Explanation: NEC 760.41 requires fire alarm circuits to be installed in separate raceways or cable assemblies. Question 49. What is the required size of the equipment grounding conductor for a 60 A circuit protected by a 60 A breaker, using copper? A) 12 AWG B) 10 AWG C) 8 AWG D) 6 AWG Answer: B Explanation: Table 250.122 specifies 10 AWG copper for a 60 A overcurrent device. Question 50. Which of the following is an acceptable method for grounding a metal water pipe that is used as a grounding electrode? A) Connect a GEC with a listed clamp within 5 ft of the service. B) Use a non-listed clamp. C) No connection needed if the pipe is buried. D) Tie the pipe to the neutral with a wire-nut. Answer: A Explanation: The GEC must be connected with a listed clamp within 5 ft of the service disconnect. Question 51. A 30 kW, 480 V three-phase motor requires a protective device. Which breaker size is the minimum allowed per NEC 430.32?
531SD Contractor Ultimate Exam
A) 40 A
B) 45 A
C) 50 A
D) 60 A
Answer: B Explanation: Motor FLC ≈ 30 kW ÷ (√3×480) ≈ 36 A; 125 % = 45 A, so a 45 A breaker is the minimum. Question 52. **Which NEC article addresses the requirements for conduit systems? ** A) Article 300 B) Article 310 C) Article 358 D) Article 376 Answer: C Explanation: Article 358 covers electrical metallic tubing (EMT), a common conduit type. Question 53. In a dwelling unit, the required number of receptacles in a kitchen countertop space is based on which NEC rule? A) One receptacle per 12 in. of countertop width. B) One receptacle per 24 in. of countertop width. C) One receptacle per 36 in. of countertop width. D) No specific requirement; any number is acceptable. Answer: B Explanation: NEC 210.52(C)(1) requires a receptacle outlet at intervals not exceeding 24 in. Question 54. Which of the following is the correct size for a grounding electrode conductor (GEC) attached to a 100 A service using aluminum? A) 6 AWG aluminum
531SD Contractor Ultimate Exam
Answer: B Explanation: Load = 0.4 × 100 kW = 40 kW. Current = 40,000 W ÷ 240 V = 166.7 A; next standard size is 175 A. Question 58. Which of the following is a permitted method for bonding a metal conduit to a grounding electrode? A) Using a listed bonding jumper within 5 ft of the electrode. B) Wrapping the conduit around the electrode. C) No bonding required if conduit is continuous. D) Using a non-listed clamp. Answer: A Explanation: NEC 250.118 permits bonding with a listed jumper within 5 ft of the electrode. Question 59. A 120 V, 15 A receptacle is installed in a residential bathroom. Which protection is required? A) No special protection. B) GFCI protection. C) AFCI protection only. D) Both GFCI and AFCI. Answer: B Explanation: NEC 210.8(A)(1) requires GFCI protection for bathroom receptacles. Question 60. What is the maximum allowable voltage drop for feeder conductors supplying a single-family dwelling? A) 2 % B) 3 % C) 5 % D) 10 % Answer: B Explanation: NEC recommends a maximum of 3 % voltage drop for feeders.
531SD Contractor Ultimate Exam
Question 61. Which NEC article governs the installation of low-voltage (less than 50 V) circuits? A) Article 300 B) Article 725 C) Article 770 D) Article 800 Answer: C Explanation: Article 770 addresses low-voltage lighting systems (< 50 V). Question 62. A 250 kVA, 13.8 kV/480 V transformer is installed with a primary overcurrent protective device of 300 A. What is the appropriate secondary protective device rating? A) 150 A B) 200 A C) 250 A D) 300 A Answer: B Explanation: Secondary full-load current ≈ 300 kVA ÷ (√ 3 ×480) ≈ 360 A; however, NEC 450.3 requires the secondary protective device not to exceed 125 % of the secondary full-load current, so a 450 A device would be required. The nearest standard size is 500 A. (Correct answer: D) Question 63. Which of the following is required for a receptacle installed in a laundry room? A) AFCI protection only. B) GFCI protection only. C) Both AFCI and GFCI protection. D) No special protection. Answer: B Explanation: NEC 210.8(A)(7) requires GFCI protection for laundry receptacles.
