California C-10 Electrical Contractor
Exam 2025/2026 – Questions &
Answers with Rationales | 100%
Verified | Graded A+
This document provides 100 multiple-choice questions with verified answers and rationales for
the 2025 California C-10 Electrical Contractor License Exam, administered by the Contractors
State License Board (CSLB) through PSI testing centers. The questions cover key topics such as
electrical codes (2023 National Electrical Code), safety standards (Title 8 Health & Safety
Orders), wiring methods, load calculations, and business management, per CSLB and NEC
guidelines. Answers are in dark red, with rationales to deepen understanding. This resource is
designed to help candidates achieve the required 72% passing score for the C-10 license, which
covers electrical installations, repairs, and maintenance in residential, commercial, and industrial
settings.
California C-10 Electrical Contractor Exam Questions (1–
100)
1. What is the minimum size grounding electrode conductor for a 200-amp service
using copper?
o A) 2 AWG
o B) 4 AWG
o C) 6 AWG
o D) 8 AWG
o Answer: B. 4 AWG
o Rationale: Per NEC Table 250.66, a 4 AWG copper conductor is required for a
200-amp service.
2. What is required for all underground service conductors?
o A) Aluminum wiring
o B) Conduit protection
o C) Aerial support
o D) Weatherproof enclosures
o Answer: B. Conduit protection
o Rationale: NEC 230.50 requires underground conductors to be protected by
approved raceways or conduits to prevent physical damage.
,3. What is the standard voltage supplied to most U.S. homes?
o A) 208/120V
o B) 240/120V
o C) 277/480V
o D) 120V only
o Answer: B. 240/120V
o Rationale: Typical residential service includes two 120V legs, providing a total
of 240V.
4. What is the color code for the ground wire in residential wiring?
o A) Black
o B) Red
o C) Green or bare
o D) White
o Answer: C. Green or bare
o Rationale: NEC 250.119 requires ground wires to be green or bare copper.
5. What is the minimum size copper conductor for a 20-amp circuit?
o A) 16 AWG
o B) 14 AWG
o C) 12 AWG
o D) 10 AWG
o Answer: C. 12 AWG
o Rationale: NEC 210.19(A)(4) mandates at least 12 AWG copper for 20-amp
circuits.
6. How often must an electrical contractor license be renewed in California?
o A) Every 10 years
o B) Every 2 to 3 years
o C) Annually
o D) Never
o Answer: B. Every 2 to 3 years
o Rationale: California requires license renewal every 2 years for sole owners and
3 years for non-sole owners.
7. Which location requires GFCI protection?
o A) Bedroom outlets
o B) Bathroom outlets
o C) Living room outlets
o D) Basement lighting
o Answer: B. Bathroom outlets
o Rationale: NEC 210.8 requires GFCI protection in wet locations like bathrooms.
8. What is the function of an overcurrent protection device (OCPD)?
o A) Increases current flow
o B) Prevents wire overheating
o C) Stabilizes voltage
o D) Amplifies power
o Answer: B. Prevents wire overheating
o Rationale: OCPDs, like breakers and fuses, prevent excessive current from
overheating wires.
, 9. What is the required height for mounting a wall switch in a commercial setting?
o A) 36 inches
o B) 42 inches
o C) 48 inches
o D) 60 inches
o Answer: C. 48 inches
o Rationale: Per ADA and NEC standards, switches are mounted at a maximum of
48 inches from the floor.
10. Which drawing shows the overall layout of a building’s electrical system?
o A) Schematic diagram
o B) Plan view (floor plan)
o C) Riser diagram
o D) Elevation drawing
o Answer: B. Plan view (floor plan)
o Rationale: Plan views show the location of devices, wiring, and panels across the
floor layout.
11. What is the minimum cover depth for a direct-buried PVC conduit under a
residential driveway?
o A) 12 inches
o B) 18 inches
o C) 24 inches
o D) 6 inches
o Answer: B. 18 inches
o Rationale: CEC 300.5 requires a minimum cover depth of 18 inches for PVC
conduit under driveways.
12. How many conductors does a device yoke count as for box fill calculations?
o A) One conductor
o B) Two conductors
o C) Three conductors
o D) Four conductors
o Answer: B. Two conductors
o Rationale: CEC 314.16(B)(4) states that each device yoke counts as a two-
conductor volume allowance.
13. What is the minimum size equipment grounding conductor for a 100-amp circuit
using THWN conductors?
o A) 8 AWG
o B) 6 AWG
o C) 4 AWG
o D) 10 AWG
o Answer: A. 8 AWG
o Rationale: Per 2023 NEC Table 250.122, an 8 AWG conductor is required for a
100-amp circuit.
14. What is the maximum number of 12 AWG THHN conductors permitted in a 3/4-
inch EMT conduit?
o A) 16
o B) 22
Exam 2025/2026 – Questions &
Answers with Rationales | 100%
Verified | Graded A+
This document provides 100 multiple-choice questions with verified answers and rationales for
the 2025 California C-10 Electrical Contractor License Exam, administered by the Contractors
State License Board (CSLB) through PSI testing centers. The questions cover key topics such as
electrical codes (2023 National Electrical Code), safety standards (Title 8 Health & Safety
Orders), wiring methods, load calculations, and business management, per CSLB and NEC
guidelines. Answers are in dark red, with rationales to deepen understanding. This resource is
designed to help candidates achieve the required 72% passing score for the C-10 license, which
covers electrical installations, repairs, and maintenance in residential, commercial, and industrial
settings.
California C-10 Electrical Contractor Exam Questions (1–
100)
1. What is the minimum size grounding electrode conductor for a 200-amp service
using copper?
o A) 2 AWG
o B) 4 AWG
o C) 6 AWG
o D) 8 AWG
o Answer: B. 4 AWG
o Rationale: Per NEC Table 250.66, a 4 AWG copper conductor is required for a
200-amp service.
2. What is required for all underground service conductors?
o A) Aluminum wiring
o B) Conduit protection
o C) Aerial support
o D) Weatherproof enclosures
o Answer: B. Conduit protection
o Rationale: NEC 230.50 requires underground conductors to be protected by
approved raceways or conduits to prevent physical damage.
,3. What is the standard voltage supplied to most U.S. homes?
o A) 208/120V
o B) 240/120V
o C) 277/480V
o D) 120V only
o Answer: B. 240/120V
o Rationale: Typical residential service includes two 120V legs, providing a total
of 240V.
4. What is the color code for the ground wire in residential wiring?
o A) Black
o B) Red
o C) Green or bare
o D) White
o Answer: C. Green or bare
o Rationale: NEC 250.119 requires ground wires to be green or bare copper.
5. What is the minimum size copper conductor for a 20-amp circuit?
o A) 16 AWG
o B) 14 AWG
o C) 12 AWG
o D) 10 AWG
o Answer: C. 12 AWG
o Rationale: NEC 210.19(A)(4) mandates at least 12 AWG copper for 20-amp
circuits.
6. How often must an electrical contractor license be renewed in California?
o A) Every 10 years
o B) Every 2 to 3 years
o C) Annually
o D) Never
o Answer: B. Every 2 to 3 years
o Rationale: California requires license renewal every 2 years for sole owners and
3 years for non-sole owners.
7. Which location requires GFCI protection?
o A) Bedroom outlets
o B) Bathroom outlets
o C) Living room outlets
o D) Basement lighting
o Answer: B. Bathroom outlets
o Rationale: NEC 210.8 requires GFCI protection in wet locations like bathrooms.
8. What is the function of an overcurrent protection device (OCPD)?
o A) Increases current flow
o B) Prevents wire overheating
o C) Stabilizes voltage
o D) Amplifies power
o Answer: B. Prevents wire overheating
o Rationale: OCPDs, like breakers and fuses, prevent excessive current from
overheating wires.
, 9. What is the required height for mounting a wall switch in a commercial setting?
o A) 36 inches
o B) 42 inches
o C) 48 inches
o D) 60 inches
o Answer: C. 48 inches
o Rationale: Per ADA and NEC standards, switches are mounted at a maximum of
48 inches from the floor.
10. Which drawing shows the overall layout of a building’s electrical system?
o A) Schematic diagram
o B) Plan view (floor plan)
o C) Riser diagram
o D) Elevation drawing
o Answer: B. Plan view (floor plan)
o Rationale: Plan views show the location of devices, wiring, and panels across the
floor layout.
11. What is the minimum cover depth for a direct-buried PVC conduit under a
residential driveway?
o A) 12 inches
o B) 18 inches
o C) 24 inches
o D) 6 inches
o Answer: B. 18 inches
o Rationale: CEC 300.5 requires a minimum cover depth of 18 inches for PVC
conduit under driveways.
12. How many conductors does a device yoke count as for box fill calculations?
o A) One conductor
o B) Two conductors
o C) Three conductors
o D) Four conductors
o Answer: B. Two conductors
o Rationale: CEC 314.16(B)(4) states that each device yoke counts as a two-
conductor volume allowance.
13. What is the minimum size equipment grounding conductor for a 100-amp circuit
using THWN conductors?
o A) 8 AWG
o B) 6 AWG
o C) 4 AWG
o D) 10 AWG
o Answer: A. 8 AWG
o Rationale: Per 2023 NEC Table 250.122, an 8 AWG conductor is required for a
100-amp circuit.
14. What is the maximum number of 12 AWG THHN conductors permitted in a 3/4-
inch EMT conduit?
o A) 16
o B) 22
