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CSLB C-10 Electrical Contractor practice questions

210 free questions with answers and explanations.

Practice test
  1. 51.A technician must install 8 current-carrying 10 AWG THHN conductors in a single EMT raceway. Using a 40% fill allowance, what is the minimum trade size of EMT required?Wiring Methods and Materials
  2. 52.A single-gang nonmetallic device box is marked with an interior volume of 18 cubic inches. It contains one duplex receptacle, two 14/2 NM-B cables (4 current-carrying 14 AWG conductors), and one internal cable clamp. Using NEC Table 314.16(B), where each 14 AWG conductor requires 2.0 in³ per allowance, what is the total required volume, and does the box comply?Wiring Methods and Materials
  3. 53.An 8-foot length of flexible metal conduit (FMC) is used to connect to a vibrating pump motor on a 20A branch circuit. No separate equipment grounding conductor is installed inside the FMC. Does this installation comply with NEC requirements for using the conduit as the equipment ground path?Wiring Methods and Materials
  4. 54.A commercial lighting track installation runs 24 feet along a ceiling in a retail store. Per NEC 220.43(B), track lighting loads are calculated at 150 VA for every 2 feet of track length. If this track is supplied by a single 120-volt branch circuit, what is the minimum calculated current the circuit must be able to supply?Equipment and Installation
  5. 55.A technician must run 9 current-carrying 10 AWG THHN conductors (0.0211 sq in each) in a single EMT raceway. Using the 40% fill allowance from NEC Chapter 9, Table 4 (1/2 inch EMT = 0.122 sq in at 40%; 3/4 inch EMT = 0.213 sq in at 40%), what is the minimum trade size EMT conduit required?Equipment and Installation
  6. 56.A PVC conduit run is installed outdoors along a parking structure where temperature swings will cause significant thermal movement. According to NEC 352.44, when must an expansion fitting be installed in the run?Wiring Methods and Materials
  7. 57.A client plans to install a new central air conditioning unit requiring a 240V, 30A dedicated circuit. The unit is located 60 feet from the service panel. The contractor estimates the total voltage drop should not exceed 3%. What is the minimum AWG conductor size required, assuming copper conductors (K=12.9) and a 75°C termination rating?Planning and Estimating
  8. 58.A lighting layout on a blueprint shows a linear array of LED strip lights, with each section requiring 50 VA. The entire run consists of 10 sections. The circuit is 120V. When performing a material takeoff for the overcurrent protection, what is the minimum required amperage for the branch circuit overcurrent protective device if these lights are considered a continuous load?Planning and Estimating
  9. 59.A homeowner asks an electrician to install a surface-mounted luminaire with a completely enclosed light source (incandescent) on the wall inside a clothes closet. Per NEC 410.16, what is the minimum clearance required between this luminaire and the nearest point of the closet storage space?Equipment and Installation
  10. 60.A technician is performing a material takeoff for a commercial kitchen. The plan calls for wiring a 208V, 3-phase, 3-wire circuit to a 10 kW oven. The circuit will use three current-carrying conductors. What is the approximate continuous current draw of this oven?Planning and Estimating
  11. 61.An engineer calculates the available fault current at a new panelboard to be 42,000 amperes. Which of the following circuit breakers may be installed to comply with NEC 110.9 interrupting rating requirements?Equipment and Installation
  12. 62.An electrician is reviewing blueprints for a new commercial building. The general notes specify that all branch circuit conductors for 120V and 277V lighting are to be sized assuming a 3% voltage drop and a 75°C termination temperature. What section of the CEC provides general guidelines and requirements for conductor ampacity and temperature limitations?Planning and Estimating
  13. 63.A contractor installs new fluorescent luminaires with ballasts in a commercial warehouse. The ballasts are designed to be serviced in place. Per NEC 410.130(G), what is required for these luminaires?Equipment and Installation
  14. 64.An electrician installs a 125-volt, 15-ampere receptacle on a countertop 4 feet from the edge of a sink in an employee break room within a commercial office building. Per NEC 210.8(B), is GFCI protection required for this receptacle?Equipment and Installation
  15. 65.A contractor is estimating the cost for a new branch circuit in a retail store. The circuit will be 120V and serve six display lights, each with a total load of 75 VA. The circuit breaker is 20A. What is the total estimated continuous load VA for these display lights, requiring the 125% adjustment for the OCPD?Planning and Estimating
  16. 66.An electrician needs to extend an existing 120-volt, 15-ampere bedroom branch circuit by 4 feet to relocate a single receptacle outlet, with no additional outlets added. The existing circuit is not currently AFCI protected. Per NEC 210.12(B) Exception, is AFCI protection required for this extension?Equipment and Installation
  17. 67.A contractor installs conduit in a Class I, Division 1 hazardous location that terminates at an enclosure housing switches capable of arcing, sparking, or high temperatures. Per NEC 501.15, within what maximum distance from the enclosure must a sealing fitting be installed in this raceway?Equipment and Installation
  18. 68.When performing a material takeoff for a series of recessed lighting fixtures, the electrician needs to identify the type of cable specified. The blueprint legend indicates 'NM-B' cable. Which of the following best describes the appropriate use and characteristics of NM-B cable?Planning and Estimating
  19. 69.A commercial client requires a new 120V, 20A branch circuit for a series of general-use receptacles in an office space. The blueprints specify that the circuit will be wired with 12 AWG THHN conductors in EMT conduit. What is the minimum internal cross-sectional area (in square inches) required for the EMT conduit to properly accommodate these conductors, assuming a 40% fill limit and standard conductor areas?Planning and Estimating
  20. 70.A blueprint indicates a symbol consisting of a circle with two diagonal lines crossing through it, and a 'WP' subscript. What does this symbol typically represent in an electrical drawing?Planning and Estimating
  21. 71.During a site visit for a commercial tenant improvement, an electrician observes that a portion of the existing lighting circuit wiring is visibly damaged. The circuit is 120V and serves 10 fluorescent light fixtures, each drawing 1.5A. The damaged wiring needs to be replaced and potentially extended. What is the minimum continuous current rating the new overcurrent protective device (OCPD) must have for this lighting circuit, assuming it's a general lighting load?Planning and Estimating
  22. 72.A 3-phase feeder supplies three continuous-duty induction motors with full-load currents of 12A, 18A, and 24A per Table 430.250. Per NEC 430.24, what is the minimum ampacity required for the feeder conductors supplying all three motors?Equipment and Installation
  23. 73.An electrical contractor is planning for a new commercial office building. The blueprints indicate a main service conduit run of 150 feet from the utility transformer to the main service panel. The planned service is 480Y/277V, 3-phase. Which of the following conduit types would be most appropriate for this underground service entrance, considering mechanical protection and resistance to environmental factors?Planning and Estimating
  24. 74.An electrician installs a multiwire branch circuit consisting of two ungrounded conductors and a shared neutral, supplying receptacles in a kitchen. The circuit uses two single-pole circuit breakers without a handle tie or common-trip mechanism. Does this installation comply with NEC 210.4(B)?Equipment and Installation
  25. 75.A contractor is preparing a material takeoff for a new branch circuit. The circuit will consist of three 12 AWG THHN conductors and one 12 AWG bare copper grounding conductor installed in a 3/4-inch EMT conduit. What is the maximum number of additional 12 AWG THHN conductors that can be added to this conduit without exceeding the 40% fill limit, assuming a standard cross-sectional area for 12 AWG THHN?Planning and Estimating
  26. 76.A technician is sizing branch-circuit conductors for a hermetic refrigerant motor-compressor. The compressor nameplate lists a rated-load current (RLC) of 22 amperes and a branch-circuit selection current of 26 amperes. Per NEC 440.6, which value must be used to size the branch-circuit conductors?Equipment and Installation
  27. 77.A client wants to install a new dedicated 240V, 30A circuit for an electric vehicle (EV) charger in their garage. The charger is located 80 feet from the main service panel. Assuming THHN conductors in conduit and a maximum voltage drop of 3% for the branch circuit, what is the minimum acceptable conductor size (AWG) that should be used?Planning and Estimating
  28. 78.A blueprint for a small commercial tenant improvement shows a symbol for a duplex receptacle with a small 'G' inside a triangle next to it. What does this symbol indicate?Planning and Estimating
  29. 79.A residential client requests an electrical service upgrade. The existing service is 100A, 120/240V. The new load calculation, per Article 220 of the CEC, includes 2500 sq ft of living space, a 12 kW electric range, a 4.5 kW water heater, and a 5 kW dryer. What is the minimum standard service size required for this dwelling?Planning and Estimating
  30. 80.An electrician installs a lighting and appliance branch-circuit panelboard equipped entirely with plug-in circuit breakers, fed from a single main breaker. Per NEC 408.36, what is the maximum number of overcurrent protective devices (poles/circuits), not counting the main, that this type of panelboard is permitted to contain?Equipment and Installation
  31. 81.A residential client is planning a new laundry room. The plans specify a 120V, 20A branch circuit for the washing machine and a separate 120V, 20A branch circuit for the gas dryer receptacle. What is the minimum load (in VA) that must be calculated for the laundry branch circuit, according to NEC 220.52(B)?Planning and Estimating
  32. 82.A commercial building client is planning a new general office area. The electrical plans specify 120V, 20A branch circuits for general-purpose receptacle outlets. The total floor area of the office space is 3000 square feet. According to NEC 220.14(J), what is the minimum general lighting load (in VA) that must be used for calculations for this office area?Planning and Estimating
  33. 83.A client requests a material takeoff for a new residential kitchen. The plans specify a 20A, 120V small-appliance branch circuit. How many duplex receptacles are typically included in the material calculation for a single small-appliance branch circuit in a kitchen, according to general residential wiring practices and the NEC?Planning and Estimating
  34. 84.A commercial kitchen requires a new 208V, 3-phase, 50A circuit for a combination oven. The circuit will be run in EMT conduit. The plans specify using three 6 AWG THHN copper conductors and one 10 AWG THHN copper equipment grounding conductor. What is the minimum trade size of EMT conduit required for this installation?Planning and Estimating
  35. 85.A client is upgrading the service for a single-family dwelling. The existing service is 100A, and the proposed upgrade is to 200A. The main service panel is located 60 feet from the utility transformer and meter. What is the minimum size of service entrance conductors (copper, THWN-2) required for this 200A service, assuming the conductors are installed in conduit?Planning and Estimating
  36. 86.An electrician is performing a material takeoff for a new service entrance to a small commercial building. The service will consist of four 3/0 AWG THHN copper conductors. What is the minimum trade size of rigid metal conduit (RMC) required to enclose these conductors, assuming a straight run?Planning and Estimating
  37. 87.A material takeoff for a new residential construction includes several 120V, 15A lighting branch circuits. The plans specify using 14 AWG THHN conductors. What is the maximum number of 14 AWG THHN conductors permitted in a 1/2-inch trade size EMT conduit, assuming all conductors are current-carrying?Planning and Estimating
  38. 88.A client requests a material takeoff for a new 120V, 20A general-purpose branch circuit. The circuit will primarily serve wall receptacles in a typical residential living room. According to NEC general provisions, what is the minimum load (in VA) that must be allocated for each general-purpose receptacle for calculation purposes, if no specific appliance is connected?Planning and Estimating
  39. 89.A contractor is preparing a material takeoff for a new commercial retail space. The plans indicate the use of flexible metal conduit (FMC) for connecting several recessed lighting fixtures to a junction box. The circuit will use three 12 AWG THHN conductors. What is the maximum number of 12 AWG THHN conductors permitted in a 3/8-inch trade size FMC, assuming all conductors are current-carrying?Planning and Estimating
  40. 90.A residential client is planning to install a new electric vehicle charger. The charger is rated at 240V, 40A. The existing service is a 200A, 120/240V single-phase dwelling service. The main service panel is located 75 feet from the proposed EV charger location. What is the minimum size copper conductor required for this circuit to limit voltage drop to approximately 3%?Planning and Estimating
  41. 91.An electrical contractor is reviewing blueprints for a new commercial office building. The blueprints indicate a symbol that is a square with a diagonal line from one corner to the opposite, with the letter 'R' inside. What does this symbol typically represent?Planning and Estimating
  42. 92.A client has provided blueprints for a new commercial warehouse. The electrical plans indicate a symbol consisting of a triangle with the letter 'P' inside, and an arrow pointing away from one side. What does this symbol typically represent?Planning and Estimating
  43. 93.A commercial building renovation requires a new 480V, 3-phase, 100A feeder for a motor control center. The feeder will run 150 feet from the main distribution panel. What is the minimum size of THHN copper conductor required, assuming a maximum 3% voltage drop and considering an ambient temperature of 30°C?Planning and Estimating
  44. 94.A material takeoff for a new commercial office space includes several lighting branch circuits. Each circuit is 120V, 20A, and will supply 12 fluorescent lighting fixtures, each drawing 1.5A. The circuit will be protected by a circuit breaker. What is the minimum continuous load rating (in VA) that must be used for sizing the overcurrent protective device for each circuit?Planning and Estimating
  45. 95.A 240V single-phase heating element draws 20 amps. What is the total power consumed by the element?Electrical Theory and Calculations
  46. 96.A conduit run needs to accommodate 4 AWG THHN conductors. According to NEC Table C.1 or relevant conduit fill calculations, what is the maximum number of 4 AWG THHN conductors permitted in a 1-1/2 inch EMT conduit?Electrical Theory and Calculations
  47. 97.An electrician is troubleshooting a control circuit that has a 24V supply. If a relay coil in the circuit draws 50 mA of current, what is the resistance of the relay coil?Electrical Theory and Calculations
  48. 98.A 120V circuit powers a resistive heating element with a resistance of 10 ohms. What is the approximate current drawn by the heating element?Electrical Theory and Calculations
  49. 99.A circuit has three resistors connected in series: R1 = 10 ohms, R2 = 20 ohms, and R3 = 30 ohms. If the total voltage supplied to the circuit is 120 volts, what is the total current flowing through the circuit?Electrical Theory and Calculations
  50. 100.A series circuit contains three resistors: R1 = 20 ohms, R2 = 30 ohms, and R3 = 50 ohms. If the circuit is connected to a 120V DC source, what is the total resistance of the circuit?Electrical Theory and Calculations