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CSLB C-10 Electrical Contractor practice questions

210 free questions with answers and explanations.

Practice test
  1. 1.A metal wireway has an interior cross-sectional area of 12 square inches. Per NEC 376.22(A), conductors may occupy no more than 20% of this area. What is the maximum allowable conductor fill area?Wiring Methods and Materials
  2. 2.A commercial building has a 400A, 208Y/120V service. The design calls for six individual circuit breakers, each rated at various ampacities, mounted together in one panelboard enclosure to serve as the building's service disconnecting means, with no single main breaker. Is this arrangement permitted under the CEC?Equipment and Installation
  3. 3.A two-gang metal device box contains one duplex receptacle and one single-pole switch (each on its own yoke), plus two 12/2 NM-B cables entering the box (4 current-carrying 12 AWG conductors and grounding conductors). Using the box fill allowances of NEC 314.16, what is the minimum required box volume?Wiring Methods and Materials
  4. 4.A 3-phase, 4-wire feeder supplies a panelboard with a continuous lighting load of 150 amperes and a non-continuous receptacle load of 40 amperes. What is the minimum required ampacity for the feeder conductors before any temperature correction or adjustment factors?Equipment and Installation
  5. 5.A technician drives a single 8-foot ground rod at a residence and measures 32 ohms of resistance to earth using a ground resistance tester. Per NEC 250.53(A)(2), what must the technician do?Wiring Methods and Materials
  6. 6.What is the primary purpose of the grounding electrode conductor (GEC) at a dwelling service?Wiring Methods and Materials
  7. 7.A 3-phase, 480V motor has a nameplate FLC of 34 amperes. Using copper THWN-2 conductors terminated on 75°C-rated terminals, what is the minimum standard conductor size required per NEC 430.22 for this motor's branch-circuit conductors? (Use NEC Table 310.16.)Equipment and Installation
  8. 8.A homeowner is having new branch circuits installed inside the wood-framed walls of a single-family dwelling in a dry, unexposed location. Which cable type is most commonly specified for this concealed interior wiring?Wiring Methods and Materials
  9. 9.An electrician terminates aluminum THHN conductors onto a device that is listed and rated for use with aluminum conductors (marked AL-CU). What additional step should be taken at the termination to help prevent oxidation and ensure a reliable long-term connection?Wiring Methods and Materials
  10. 10.A continuous 30A load is supplied by copper THWN conductors terminating on breakers rated for 75°C. Using the 125% continuous load factor and NEC Table 310.16 (75°C column), what is the minimum conductor size required?Wiring Methods and Materials
  11. 11.A journeyman is installing a 277/480-volt panelboard against a grounded masonry wall. The front of the panelboard will have exposed energized parts when the dead front is removed, and the opposite wall is grounded masonry. What minimum working clearance in front of the panelboard does the CEC require?Equipment and Installation
  12. 12.A rigid metal conduit (RMC) run will be installed underground and encased in concrete that is in direct contact with corrosive soil. Per NEC 344.10(B), what additional protection is required?Wiring Methods and Materials
  13. 13.A rooftop HVAC condensing unit motor requires a flexible raceway connection that will be exposed to rain and vibration. Which raceway type is best suited for this application?Wiring Methods and Materials
  14. 14.An electrician is wiring new 120-volt, 20-ampere branch circuits in a single-family dwelling. Per NEC 210.12, which of the following locations is NOT required to have AFCI protection?Equipment and Installation
  15. 15.A dwelling service is supplied by 400 kcmil copper THHN service-entrance conductors. Per NEC Table 250.66, what is the minimum size copper grounding electrode conductor (GEC) required?Wiring Methods and Materials
  16. 16.A contractor installs Type SE cable as a feeder from the main service panel to a detached garage subpanel. Which of the following wiring requirements applies to this installation?Wiring Methods and Materials
  17. 17.A raceway will contain one 4 AWG THHN copper conductor (0.0824 in²), two 8 AWG THHN copper conductors (0.0366 in² each), and two 10 AWG THHN copper conductors (0.0211 in² each). Using the 40% fill rule for three or more conductors, what is the minimum trade size EMT required?Wiring Methods and Materials
  18. 18.A single-phase motor has a nameplate FLC of 40 amperes. The installer plans to use an inverse-time circuit breaker for branch-circuit short-circuit and ground-fault protection. Per NEC Table 430.52, what is the maximum standard breaker size permitted without invoking any exception?Equipment and Installation
  19. 19.An engineer specifies two 3/0 AWG THHN copper conductors per phase, installed in parallel in separate conduits, to serve a 400A load. Each 3/0 AWG THHN conductor has an adjusted allowable ampacity of 225A. What is the total allowable ampacity of the parallel conductor set per phase, per NEC 310.10(H)?Wiring Methods and Materials
  20. 20.According to NEC 362.10, in which of the following locations may Electrical Nonmetallic Tubing (ENT) be installed without additional protective measures?Wiring Methods and Materials
  21. 21.An electrician installs a straight run of EMT conduit along an exposed wall in a commercial building. According to the NEC, EMT must be securely fastened within 3 feet of each outlet box and at what maximum interval along the remaining run?Wiring Methods and Materials
  22. 22.A ladder-type cable tray is 18 inches wide and will contain multiple single-conductor Type XHHW cables sized 1000 kcmil, each 1.2 inches in diameter. Per NEC 392.22(A)(1), for single conductors sized 1000 kcmil and larger, the sum of the cable diameters must not exceed the tray width. What is the maximum number of these cables permitted in the tray?Wiring Methods and Materials
  23. 23.An electrician installs a subpanel in a detached garage fed from the main dwelling panel by a 4-wire feeder (two hots, a neutral, and an equipment grounding conductor). At the subpanel, how must the neutral and equipment grounding conductor be terminated?Equipment and Installation
  24. 24.A contractor is wiring equipment inside a grain elevator classified as a Class II, Division 1 location due to the presence of combustible dust. Which wiring method is acceptable for this installation?Equipment and Installation
  25. 25.A UF cable supplies a 120V, 20A GFCI-protected branch circuit to a detached storage shed. The cable does not run under a driveway or area subject to vehicular traffic. Per NEC Table 300.5, what is the minimum required burial depth?Wiring Methods and Materials
  26. 26.A 120-volt lighting branch circuit uses 12 AWG copper conductors (K=12.9) to supply a 12-ampere load located 150 feet from the panel (one-way distance). Using the formula VD = (2 × K × I × D) / CM, what is the approximate percentage voltage drop on this circuit?Equipment and Installation
  27. 27.A residential kitchen circuit uses a multiwire branch circuit with two ungrounded conductors sharing a common neutral, feeding two separate 120V receptacle circuits. Per NEC 210.4(B), what is required at the panelboard?Wiring Methods and Materials
  28. 28.A dedicated lighting branch circuit supplies a continuous load of 32 amperes for 4+ hours daily. What is the minimum standard overcurrent device size required for this branch circuit conductor?Equipment and Installation
  29. 29.A 3-phase induction motor has a nameplate full-load current (FLC) of 28 amperes and a marked service factor of 1.15. Per NEC 430.32, what is the maximum permitted overload device setting for continuous-duty protection of this motor?Equipment and Installation
  30. 30.A pool contractor installs an equipotential bonding grid around a new in-ground swimming pool using a solid 8 AWG copper conductor connecting the reinforcing steel, pool perimeter surfaces, and metal fittings within 3 feet of the pool wall. Per NEC 680.26, is this bonding grid required to be connected to the electrical service grounding electrode system?Equipment and Installation
  31. 31.A 25-horsepower, 230-volt, 3-phase motor has a Table 430.250 full-load current of 68 amperes. What is the minimum ampere rating required for the motor's disconnecting means switch?Equipment and Installation
  32. 32.A single-phase, dry-type transformer rated 4.5 kVA has a 480-volt primary. The calculated primary full-load current is 9.4 amperes. Per NEC Table 450.3(B), since the primary current exceeds 9 amperes, the maximum primary overcurrent protection allowed is 125% of FLC. What is the maximum standard primary overcurrent device rating permitted?Equipment and Installation
  33. 33.A 6 AWG THHN copper conductor is installed to feed equipment with terminals rated for 75°C. Per NEC 110.14(C), what ampacity must be used for this conductor even though THHN insulation is rated for 90°C?Wiring Methods and Materials
  34. 34.A raceway will contain three 4/0 AWG THHN copper service conductors plus one 4 AWG THHN equipment grounding conductor. Using Chapter 9, Table 5 conductor areas (4/0 = 0.3237 in², 4 AWG = 0.0824 in²) and the 40% fill rule, what is the minimum trade size EMT required?Wiring Methods and Materials
  35. 35.A homeowner asks an electrician to add a new 20-ampere, 120-volt receptacle circuit to serve small kitchen countertop appliances. Per the CEC, what protection must this receptacle have?Equipment and Installation
  36. 36.A homeowner asks why standard Type MC cable cannot be buried directly underground without additional protection. Which characteristic of standard MC cable explains this limitation?Wiring Methods and Materials
  37. 37.A run of EMT conduit contains several 90-degree bends and offsets installed between two pull points. According to NEC 358.26, what is the maximum total number of degrees of bend permitted between pull points?Wiring Methods and Materials
  38. 38.An electrician installs NM-B cable into a metal single-gang device box equipped with an internal cable clamp. Per NEC 334.30, within what maximum distance from the box must the cable be secured to a framing member?Wiring Methods and Materials
  39. 39.Six 10 AWG THWN copper conductors must be installed in a single EMT raceway. Using NEC Chapter 9, Annex C, Table C.1 (EMT conductor fill for over two conductors), what is the minimum trade size EMT required?Wiring Methods and Materials
  40. 40.A 100-ampere circuit breaker protects a copper feeder circuit. According to NEC Table 250.122, what is the minimum size copper equipment grounding conductor required for this circuit?Wiring Methods and Materials
  41. 41.An electrician installs EMT into a service panel through a concentric knockout, securing it with a single locknut and bushing. A licensing inspector requires a bonding jumper be added. Why is this necessary?Wiring Methods and Materials
  42. 42.During a service equipment installation, a raceway knockout is larger than the connector, requiring the use of reducing washers. Per NEC 250.92(B), what additional measure is required to maintain a reliable equipment grounding path at service equipment?Wiring Methods and Materials
  43. 43.A homeowner wants a new 120-volt, 20-ampere receptacle installed on the exterior wall of the dwelling near the patio. What type of protection is required for this receptacle per the CEC?Equipment and Installation
  44. 44.A 208V three-phase feeder supplies a continuous 50A load located 200 feet from the panel, wired with 8 AWG copper conductors (16,510 circular mils). Using the formula VD = (√3 × K × I × D) / CM, where K = 12.9 ohms·cmil/ft for copper, what is the approximate voltage drop, and does it comply with the recommended 3% (6.24V) limit?Wiring Methods and Materials
  45. 45.A contractor is installing wiring for equipment inside a paint spray booth classified as a Class I, Division 1 hazardous location due to flammable vapors present under normal operating conditions. Which wiring method is required for this area per NEC Article 501?Equipment and Installation
  46. 46.A single-gang metal device box contains two 12/2 NM-B cables (4 current-carrying 12 AWG conductors, 2 grounds) with no internal cable clamps, and will hold one duplex receptacle. Using NEC box fill rules where each 12 AWG conductor counts as 2.25 cubic inches, what is the minimum required box volume?Wiring Methods and Materials
  47. 47.A 12-inch length of 1/2-inch EMT nipple connects two enclosures and contains four 12 AWG THHN conductors (each 0.0133 in² per NEC Chapter 9 Table 5). The 1/2-inch EMT has an internal area of 0.304 in². What is the correct fill rule that applies to this nipple, and does the total conductor area comply?Wiring Methods and Materials
  48. 48.An electrician examines a metal-jacketed cable that contains a thin aluminum bonding strip running the full length inside the spiral metal armor, providing supplemental grounding continuity along with the armor itself. This describes which cable type?Wiring Methods and Materials
  49. 49.A 400-ampere feeder OCPD supplies tap conductors run in conduit for 8 feet before terminating in a single 40-ampere panelboard. Applying the 10-foot tap rule of NEC 240.21(B)(1), what is the minimum ampacity required for the tap conductors?Equipment and Installation
  50. 50.A subpanel feeder is protected by a 60A breaker and uses copper THWN-2 conductors terminated on lugs rated 75°C. Using NEC Table 310.16, what is the minimum conductor size that may be used?Wiring Methods and Materials