CSLB C-10 Exam 2026/2027 Questions and
Answers with Rationales Guaranteed Pass
Latest Update
TABLE OF CONTENTS
1. Planning & Estimating
2. Rough Wiring
3. Finish Wiring & Trim
4. Startup, Troubleshooting & Maintenance
5. Safety
SECTION 1 — PLANNING & ESTIMATING
1. Before beginning an electrical installation, what should the contractor do
first?
A. Order all materials
B. Review the plans and specifications
C. Energize the service
D. Install receptacles
Answer: B
Rationale: Reviewing plans and specifications establishes the project scope,
system requirements, equipment locations, and applicable installation
requirements before work begins.
2. What is the primary purpose of an electrical single-line diagram?
A. Show paint colors
B. Show the electrical system distribution in simplified form
C. Show plumbing fixtures
D. Calculate labor wages
,Answer: B
Rationale: A single-line diagram represents electrical distribution equipment
and connections using simplified symbols and lines.
3. An electrical plan conflicts with the written specifications. What should the
contractor do?
A. Ignore the specifications
B. Use whichever option is cheaper
C. Request clarification before proceeding
D. Install both systems
Answer: C
Rationale: Conflicting construction documents should be clarified before
installation to prevent errors, rework, and disputes.
4. What document normally identifies the locations of electrical devices?
A. Electrical floor plan
B. Soil report
C. Plumbing schedule
D. Roofing plan
Answer: A
Rationale: Electrical floor plans commonly show receptacles, switches, lighting
fixtures, equipment, and other electrical devices.
5. What is a material takeoff?
A. A list and quantity of required materials
B. A list of employees
C. A record of accidents
D. A maintenance report
Answer: A
Rationale: A material takeoff determines the quantities of materials needed
for a project and supports estimating and procurement.
,6. A circuit requires 240 feet of conduit. If 10% is added for waste,
approximately how much should be estimated?
A. 240 ft
B. 250 ft
C. 264 ft
D. 288 ft
Answer: C
Rationale: 240 × 1.10 = 264 feet.
7. A project requires 20 receptacles at $8 each. What is the material cost
before tax?
A. $120
B. $160
C. $180
D. $200
Answer: B
Rationale: 20 × $8 = $160.
8. What is the primary purpose of estimating labor hours?
A. Determine labor cost and scheduling requirements
B. Determine the building's property value
C. Determine the customer's credit score
D. Determine the weather
Answer: A
Rationale: Labor-hour estimates help determine project cost, crew
requirements, and expected duration.
9. Which factor is most important when selecting a conductor?
, A. Conductor color only
B. Required ampacity and installation conditions
C. Brand name only
D. Length of the building
Answer: B
Rationale: Conductor selection depends on load, ampacity, temperature,
installation conditions, voltage drop considerations, and applicable code
requirements.
10. What information is especially important when sizing a feeder?
A. Wall paint color
B. Calculated load
C. Door hardware
D. Landscaping plan
Answer: B
Rationale: Feeder sizing begins with determining the calculated load that the
feeder must safely serve.
11. What is voltage drop?
A. Increase in voltage caused by a load
B. Reduction in voltage along a conductor due to impedance
C. Loss of grounding
D. Increase in conductor size
Answer: B
Rationale: Current flowing through conductor impedance causes a voltage
reduction between the source and load.
12. What generally happens to conductor voltage drop when conductor length
increases?
A. It decreases
B. It becomes zero
Answers with Rationales Guaranteed Pass
Latest Update
TABLE OF CONTENTS
1. Planning & Estimating
2. Rough Wiring
3. Finish Wiring & Trim
4. Startup, Troubleshooting & Maintenance
5. Safety
SECTION 1 — PLANNING & ESTIMATING
1. Before beginning an electrical installation, what should the contractor do
first?
A. Order all materials
B. Review the plans and specifications
C. Energize the service
D. Install receptacles
Answer: B
Rationale: Reviewing plans and specifications establishes the project scope,
system requirements, equipment locations, and applicable installation
requirements before work begins.
2. What is the primary purpose of an electrical single-line diagram?
A. Show paint colors
B. Show the electrical system distribution in simplified form
C. Show plumbing fixtures
D. Calculate labor wages
,Answer: B
Rationale: A single-line diagram represents electrical distribution equipment
and connections using simplified symbols and lines.
3. An electrical plan conflicts with the written specifications. What should the
contractor do?
A. Ignore the specifications
B. Use whichever option is cheaper
C. Request clarification before proceeding
D. Install both systems
Answer: C
Rationale: Conflicting construction documents should be clarified before
installation to prevent errors, rework, and disputes.
4. What document normally identifies the locations of electrical devices?
A. Electrical floor plan
B. Soil report
C. Plumbing schedule
D. Roofing plan
Answer: A
Rationale: Electrical floor plans commonly show receptacles, switches, lighting
fixtures, equipment, and other electrical devices.
5. What is a material takeoff?
A. A list and quantity of required materials
B. A list of employees
C. A record of accidents
D. A maintenance report
Answer: A
Rationale: A material takeoff determines the quantities of materials needed
for a project and supports estimating and procurement.
,6. A circuit requires 240 feet of conduit. If 10% is added for waste,
approximately how much should be estimated?
A. 240 ft
B. 250 ft
C. 264 ft
D. 288 ft
Answer: C
Rationale: 240 × 1.10 = 264 feet.
7. A project requires 20 receptacles at $8 each. What is the material cost
before tax?
A. $120
B. $160
C. $180
D. $200
Answer: B
Rationale: 20 × $8 = $160.
8. What is the primary purpose of estimating labor hours?
A. Determine labor cost and scheduling requirements
B. Determine the building's property value
C. Determine the customer's credit score
D. Determine the weather
Answer: A
Rationale: Labor-hour estimates help determine project cost, crew
requirements, and expected duration.
9. Which factor is most important when selecting a conductor?
, A. Conductor color only
B. Required ampacity and installation conditions
C. Brand name only
D. Length of the building
Answer: B
Rationale: Conductor selection depends on load, ampacity, temperature,
installation conditions, voltage drop considerations, and applicable code
requirements.
10. What information is especially important when sizing a feeder?
A. Wall paint color
B. Calculated load
C. Door hardware
D. Landscaping plan
Answer: B
Rationale: Feeder sizing begins with determining the calculated load that the
feeder must safely serve.
11. What is voltage drop?
A. Increase in voltage caused by a load
B. Reduction in voltage along a conductor due to impedance
C. Loss of grounding
D. Increase in conductor size
Answer: B
Rationale: Current flowing through conductor impedance causes a voltage
reduction between the source and load.
12. What generally happens to conductor voltage drop when conductor length
increases?
A. It decreases
B. It becomes zero
