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Electrician MO Exam
Question 1. Which NEC article governs the installation of motor overload protection? A) Article 430 B) Article 430- 51 C) Article 430- 30 D) Article 430- 71 Answer: A Explanation: Article 430 of the NEC contains the requirements for motor protection, including overload devices. Question 2. A three‑phase, 460 V motor requires a branch‑circuit conductor size of 4 AWG copper. What is the minimum size of the disconnecting means for this motor? A) 15 A B) 20 A C) 30 A D) 40 A Answer: C Explanation: Per NEC 430.102, the disconnect must be rated at least 125 % of the motor full‑load current; a 4 AWG copper conductor typically serves a 30 A motor. Question 3. When sizing a feeder for a 500 kVA, 480 V, three‑phase transformer, which factor must be applied to the full‑load current to determine the minimum conductor ampacity? A) 100 % B) 125 % C) 150 % D) 175 % Answer: B Explanation: NEC 310.15(B)(7) permits using 125 % of the transformer’s full‑load current for feeder conductor sizing.
Electrician MO Exam
Question 4. Which of the following is NOT a permitted wiring method in a Class I, Division 2 hazardous location? A) Rigid metal conduit (RMC) B) Flexible metal conduit (FMC) with listed fittings C) PVC conduit (non‑metallic) D) Mineral‑insulated cable (MI) Answer: C Explanation: Non‑metallic PVC conduit is prohibited in Class I, Division 2 areas because it does not provide sufficient protection against ignition. Question 5. A standby generator is rated at 200 kW. According to NEC 700, what is the minimum size of the automatic transfer switch (ATS) that must be installed? A) 150 kW B) 200 kW C) 250 kW D) 300 kW Answer: B Explanation: The ATS must be sized for the full rated load of the generator; therefore a 200 kW ATS is required. Question 6. In a solar photovoltaic (PV) array, the maximum DC conductor length from the modules to the inverter is limited by which NEC requirement? A) Voltage drop not exceeding 3 % B) OCPD rating not exceeding 125 % of conductor ampacity C) NEC 690.8(A) grounding electrode continuity D) NEC 690.9(A) rapid‑shutdown clearance Answer: A Explanation: While NEC does not prescribe a specific length, the industry practice (and NEC commentary) limits DC conductor runs to maintain voltage drop under 3 % for optimal performance.
Electrician MO Exam
Question 10. Which of the following is the correct method to calculate the short‑circuit current at a service entrance using the 250 % rule? A) Multiply the transformer secondary current by 2. B) Multiply the transformer primary current by 2. C) Multiply the transformer secondary current by 2. D) Multiply the transformer primary current by 2. Answer: A Explanation: The 250 % rule (NEC 230.71) uses 2.5 times the transformer secondary full‑load current to estimate the maximum available fault current at the service. Question 11. In a busway system, what is the maximum allowable unsupported length of a straight run of busway without a hanger, per NEC 368.30? A) 6 ft B) 10 ft C) 12 ft D) 15 ft Answer: B Explanation: NEC 368.30 permits a maximum unsupported length of 10 ft for straight busway runs. Question 12. Which NEC article specifically addresses the installation of cable trays? A) Article 320 B) Article 392 C) Article 408 D) Article 422 Answer: B Explanation: Article 392 of the NEC covers cable tray systems, including installation, loading, and grounding requirements.
Electrician MO Exam
Question 13. For a health‑care facility, what is the minimum voltage rating for a patient‑care area receptacle? A) 125 V B) 250 V C) 300 V D) 600 V Answer: B Explanation: NEC 517.12 requires receptacles in patient‑care areas to be rated for 250 V or higher to accommodate medical equipment. Question 14. A motor control circuit uses a 120 V control transformer with a 10 A primary. What is the minimum rating of the overcurrent protective device (OCPD) for the control circuit, per NEC 430.32? A) 15 A B) 20 A C) 25 A D) 30 A Answer: B Explanation: NEC 430.32 requires the OCPD for the control circuit to be sized at 125 % of the transformer primary current; 10 A × 1.25 = 12.5 A, so the next standard rating is 20 A. Question 15. Which of the following is a required feature of an emergency lighting system under NEC 700.12? A) Battery backup of at least 1 hour B) Automatic start upon loss of normal power C) Manual activation only D) Separate grounding electrode system Answer: B Explanation: NEC 700.12 mandates that emergency lighting must start automatically when the normal power source fails.
Electrician MO Exam
Explanation: Apparent power S = 120 kVA. For 480 V three‑phase, I = S / (√ 3 × V) = 120,000 / (1.732 × 480) ≈ 144 A. However, the question asks for apparent current per phase (ignoring PF), so 144 A is correct. (Correction: The answer is 144 A; option A). Question 19. In a Class II, Division 1 hazardous location, which wiring method is permitted for power circuits? A) NM‑B cable B) Rigid metal conduit (RMC) C) PVC conduit with listed fittings D) Flexible metal conduit (FMC) without fittings Answer: B Explanation: Rigid metal conduit is allowed in Class II, Division 1 areas; NM‑B and PVC are prohibited. Question 20. According to NEC 240.21, what is the maximum length allowed for a 10‑foot feeder tap from a feeder to a branch circuit? A) 5 ft B) 10 ft C) 15 ft D) 25 ft Answer: B Explanation: NEC 240.21(B)(1) permits a feeder tap not exceeding 10 ft in length. Question 21. Which of the following best defines “selective coordination” in overcurrent protection? A) All OCPDs operate simultaneously during a fault B) Downstream devices trip before upstream devices for faults within their zone C) Upstream devices always trip first to protect downstream devices D) Coordination is not required for residential installations Answer: B
Electrician MO Exam
Explanation: Selective coordination ensures that the protective device closest to the fault opens first, leaving upstream devices intact. Question 22. A commercial building requires a fire alarm system powered by an emergency source. Which NEC article governs this installation? A) Article 760 B) Article 770 C) Article 700 D) Article 690 Answer: C Explanation: Article 700 covers emergency systems, including fire alarm power supplies. Question 23. For a 120/240 V, single‑phase, 30 kW electric water heater, what is the minimum size of the branch‑circuit conductor per NEC 422.13? A) 8 AWG copper B) 6 AWG copper C) 4 AWG copper D) 2 AWG copper Answer: C Explanation: NEC 422.13 requires conductors sized for 125 % of the water heater’s load; 30 kW ÷ 240 V = 125 A; 125 % = 156 A, requiring at least 4 AWG copper. Question 24. Which of the following statements about the NEC “optional method” for service load calculation is correct? A) It can be used for any dwelling unit regardless of size B) It requires a demand factor of 100 % for all loads C) It allows the use of Table 220.84 for multi‑family dwellings D) It excludes lighting loads from the calculation Answer: C
Electrician MO Exam
Explanation: OSHA 29 CFR 1910.333 specifies PPE requirements for employees exposed to electric hazards. Question 28. Under NFPA 70E, what is the “arc‑flash boundary” for a system with an incident energy of 8 cal/cm² at the working distance? A) 4 ft B) 6 ft C) 8 ft D) 12 ft Answer: B Explanation: NFPA 70E defines the arc‑flash boundary as the distance at which the incident energy equals 1.2 cal/cm². Using the inverse‑square law, a system with 8 cal/cm² at the working distance (typically 18 in.) yields a boundary of approximately 6 ft. Question 29. A construction contract specifies “time‑and‑material” billing. Which of the following is a key characteristic of this contract type? A) Fixed total price agreed before work begins B) Payment based on actual labor hours and material costs plus a markup C) No provision for change orders D) Contractor assumes all risk for cost overruns Answer: B Explanation: Time‑and‑material contracts reimburse the contractor for actual labor and material costs, plus an agreed‑upon markup. Question 30. Which lien law provision requires a subcontractor to deliver a preliminary notice to the owner before commencing work on a construction project? A) Notice of Intent to Lien B) Preliminary Notice (also called Notice to Owner) C) Release of Lien D) Mechanic’s Lien Claim
Electrician MO Exam
Answer: B Explanation: Many states require a preliminary notice (Notice to Owner) to preserve lien rights for subcontractors. Question 31. In a three‑phase, 4‑wire feeder, what is the correct method to calculate the neutral load when the loads are balanced? A) Sum of all phase currents B) Zero, because balanced loads cancel C) 50 % of the total phase load D) Same as the phase current Answer: B Explanation: With perfectly balanced three‑phase loads, the neutral carries no current because the vector sum of the phase currents is zero. Question 32. Which NEC article governs the installation of receptacles in damp or wet locations? A) Article 406 B) Article 410 C) Article 408 D) Article 422 Answer: A Explanation: Article 406 covers receptacles, cord connectors, and attachment plugs, including requirements for damp and wet locations. Question 33. A building’s main service disconnect is rated at 400 A. According to NEC 230.71, what is the minimum fault current rating that the service‑entrance conductors must be capable of withstanding? A) 20 kA B) 30 kA C) 40 kA
Electrician MO Exam
D) 48 in. Answer: B Explanation: NEC 408.36 requires a minimum front clearance of 36 in. for panelboards to provide adequate working space. Question 37. A 250 kVA, 480 V, three‑phase transformer is installed with a 100 % duty rating. What is the minimum size of the service‑entrance conductor per NEC 310.15(B)(7)? A) 2/0 AWG copper B) 4/0 AWG copper C) 250 kcmil copper D) 300 kcmil copper Answer: B Explanation: Using Table 310.15(B)(7), a 250 kVA transformer requires a minimum of 4/0 AWG copper conductors for the service entrance. Question 38. Which NEC article addresses the installation of emergency power systems for health‑care facilities? A) Article 517 B) Article 700 C) Article 702 D) Article 690 Answer: C Explanation: Article 702 covers optional standby systems, which include emergency power for health‑care facilities. Question 39. In a commercial building, the calculated general‑lighting load is 150 kW. According to NEC 220.42, what demand factor should be applied? A) 100 % B) 90 % C) 80 %
Electrician MO Exam
D) 70 %
Answer: C Explanation: NEC 220.42 permits a demand factor of 80 % for general‑lighting loads in commercial occupancies. Question 40. Which of the following is the correct formula to calculate the three‑phase apparent power (S) in kVA? A) S = V × I ÷ 1000 B) S = √3 × V × I ÷ 1000 C) S = V × I × PF ÷ 1000 D) S = √3 × V × I × PF ÷ 1000 Answer: B Explanation: For three‑phase systems, apparent power S = √ 3 × V × I (where V is line‑to‑line voltage). Question 41. A building’s emergency lighting system must provide illumination for how long after loss of normal power, per NEC 700.12? A) 30 minutes B) 60 minutes C) 90 minutes D) 120 minutes Answer: B Explanation: NEC 700.12 requires emergency lighting to operate for at least 90 minutes for most occupancies, but for most commercial buildings the minimum is 60 minutes. (Correct answer: B – 60 minutes). Question 42. Which NEC article governs the installation of grounding electrodes for a building’s electrical system? A) Article 250 B) Article 240 C) Article 300
Electrician MO Exam
D) Full lien waiver Answer: B Explanation: An unconditional lien waiver releases lien rights for the amount already paid, without any conditions attached. Question 46. Under OSHA, which fall‑protection system is required for workers on a roof with an unprotected edge 10 ft above a lower level? A) Guardrail system only B) Personal fall arrest system (PFAS) only C) Either guardrail or PFAS D) No protection required under 15 ft Answer: C Explanation: OSHA 1926.501(b)(1) requires fall protection for edges 6 ft or higher; either guardrails, PFAS, or other approved systems may be used. Question 47. Which NEC article provides requirements for the installation of receptacles in residential kitchens? A) Article 210 B) Article 220 C) Article 210.52(C) D) Article 210. Answer: C Explanation: Article 210.52(C) specifically addresses countertop receptacle spacing in residential kitchens. Question 48. A transformer’s secondary is protected by a 250 A fuse. What is the minimum size of the grounding electrode conductor for this transformer per NEC 250.122? A) #8 copper B) #6 copper C) #4 copper
Electrician MO Exam
D) #2 copper Answer: C Explanation: Table 250.122 indicates a #4 AWG copper GEC is required for over‑current devices rated 225 A or less; for a 250 A fuse, the next size up (#2) is required. (Correct answer: D – # copper). Question 49. When performing a load calculation for a commercial office building, which load is considered a “continuous load” per NEC 210.20(A)? A) Lighting loads B) Motor loads C) HVAC fan motor loads D) Receptacle loads Answer: A Explanation: Lighting loads are considered continuous if they operate for three hours or more, per NEC 210.20(A). Question 50. Which of the following is a requirement for a fire‑rated cable tray supporting a fire‑resistive assembly? A) Must be made of non‑metallic material B) Must be installed with a minimum of 4 in. clearance from the ceiling C) Must be listed for fire‑resistive use and support the required fire‑rating of the assembly D) Must be painted with fire‑retardant coating Answer: C Explanation: Cable trays used in fire‑resistive assemblies must be listed for that purpose and maintain the assembly’s fire rating. Question 51. In a three‑phase, four‑wire feeder, the neutral conductor is required to be larger than the phase conductors when which condition exists? A) The feeder supplies only linear loads B) The feeder supplies unbalanced non‑linear loads
Electrician MO Exam
C) Category 2 D) Category 3 Answer: B Explanation: NFPA 70E PPE categories correspond to incident energy ranges; 4 cal/cm² falls within Category 1 (4–8 cal/cm²). Question 55. Which of the following is NOT a permissible method for grounding a metal raceway that serves as an equipment grounding conductor? A) Using a bonding jumper at each end of the raceway B) Using a listed bonding strap at each conduit fitting C) Relying on the continuity of the metal raceway without additional connections D) Installing a grounding electrode directly to the raceway every 20 ft Answer: D Explanation: Grounding electrodes are not installed directly to raceways; bonding is achieved through continuity or bonding jumpers/straps. Question 56. A commercial building has a 3‑phase, 480 V service with a calculated load of 250 kVA. Using the optional method, what is the minimum service‑entrance conductor size per NEC 310.15(B)(7)? A) 4/0 AWG copper B) 250 kcmil copper C) 300 kcmil copper D) 350 kcmil copper Answer: C Explanation: Table 310.15(B)(7) shows that a 250 kVA service requires a minimum of 300 kcmil copper conductors. Question 57. Which NEC article specifies the requirements for grounding of separately derived systems such as generators? A) Article 250.
Electrician MO Exam
B) Article 250. C) Article 250. D) Article 250. Answer: B Explanation: NEC 250.24 addresses grounding of separately derived systems, including generators. Question 58. In a Class II, Division 2 hazardous location, which type of conduit is permitted for power distribution? A) EMT B) PVC C) Rigid metal conduit (RMC) D) Flexible metal conduit (FMC) Answer: C Explanation: Rigid metal conduit is allowed in Class II, Division 2 locations; EMT is not permitted because it is not listed for this classification. Question 59. According to NEC 210.52(B)(1), how many receptacle outlets are required in a hallway that is 30 ft long? A) 3 B) 4 C) 5 D) 6 Answer: B Explanation: NEC 210.52(B)(1) requires receptacles at intervals not exceeding 12 ft; a 30‑ft hallway needs at least 4 receptacles (including at each end). Question 60. Which of the following best describes the purpose of a “feeder tap” as defined in NEC 240.21? A) A short extension of a feeder to a nearby load
