C-10 CSLB Electrical Contractor License Exam - Test Bank 2 (2026/2027) Page 1
CSLB C-10 Electrical Contractor
License Examination
Test Bank 2 — Edition
Real Exam Preparation Questions and Correct Answers
Total Questions: 200 Multiple-Choice Questions
Exam Format: Two separate exams - Trade and Law & Business
Passing Score: 72% (minimum required to pass)
Administration: PSI Testing Centers - Closed Book
Time Limit: Approximately 2.5 hours per exam section
Code Basis: 2022 California Electrical Code (CEC) / NEC 2020
Cognitive Levels: 30% Recall, 50% Application, 20% Analysis
Coverage: Planning, Rough Wiring, Finish, Troubleshooting, Safety
C-10 Classification: Installing, erecting, constructing, repairing, servicing, altering, or designing electrical
wiring, services, equipment, and apparatus for light, heat, and power.
This study guide is designed for exam preparation purposes and reflects 2026/2027 CSLB standards based on
the 2022 California Codes.
CSLB C-10 Electrical Contractor Exam Preparation - 200 Questions | Based on 2022 California Electrical Code
,C-10 CSLB Electrical Contractor License Exam - Test Bank 2 (2026/2027) Page 2
Table of Contents
Section 1: Planning and Estimating Q1 - Q56 28%
Section 2: Rough Wiring Q57 - Q110 27%
Section 3: Finish Wiring and Trim Q111 - Q132 11%
Section 4: Startup, Troubleshooting, and Maintenance Q133 - Q164 16%
Section 5: Safety Q165 - Q200 18%
How to Use This Exam: Each question is followed by four answer choices (A–D), with the correct answer
marked [CORRECT] and the rationale explaining the code reference and reasoning. The minimum passing
score for the actual CSLB exam is 72%.
CSLB C-10 Electrical Contractor Exam Preparation - 200 Questions | Based on 2022 California Electrical Code
,C-10 CSLB Electrical Contractor License Exam - Test Bank 2 (2026/2027) Page 3
SECTION 1: PLANNING AND ESTIMATING
Topics: Existing System Evaluation | Plan Interpretation | Electrical Calculations | Code Requirements
(NEC 210, 220, 240, 250, 310, 314, 430, 690) | Material Selection | Energy Production/Storage Planning
Q1: A contractor is evaluating an existing 1970s residence for a service upgrade. The existing 100-amp panel
uses Federal Pacific Stab-Lok breakers. What is the MOST appropriate recommendation to the homeowner?
A. Add additional breakers as needed; the existing panel can be reused up to 125 amps.
B. Recommend a complete panel replacement with a modern 200-amp service due to documented failure
history of Stab-Lok breakers. [CORRECT]
C. Replace only the failed breakers with after-market equivalents to save cost.
D. Install a subpanel adjacent to the existing panel to expand capacity.
Correct Answer: B
Rationale: Federal Pacific Stab-Lok breakers have a documented history of failure to trip under fault conditions, creating
fire and shock hazards. A complete panel replacement with a modern listed 200-amp service addresses both safety and
capacity for modern loads. Reusing, repairing, or sub-paneling off a known-defective panel violates the C-10 contractor's
duty under NEC 110.3(B) and Cal/OSHA safety expectations.
Q2: When evaluating an existing commercial service for an added EV charging load, what is the FIRST
calculation the contractor must perform?
A. Determine the size of new conductors required to handle the additional load.
B. Perform a load calculation per NEC Article 220 to verify the existing service has spare capacity.
[CORRECT]
C. Select a new main breaker size to accommodate the new load.
D. Specify the wire gauge based on the EV charger nameplate rating only.
Correct Answer: B
Rationale: NEC Article 220 governs load calculations and must be applied to verify existing service capacity before
adding any new load. Adding conductors, breakers, or chargers without an Article 220 evaluation risks overloading the
service and violates NEC 220.1. The nameplate alone is insufficient because demand factors and existing loads must be
considered.
Q3: An existing industrial facility has a 480V three-phase service with a 400-amp main breaker. The facility
wants to add a 100HP motor (FLC 124A). What existing-system factor must be evaluated BEFORE adding
the motor?
A. The color of the existing conduit for proper identification.
B. Whether the existing service and transformer kVA can handle the motor's starting (inrush) current
without voltage sag. [CORRECT]
C. The brand of the existing breakers for matching purposes.
D. The age of the existing grounding electrode conductor.
Correct Answer: B
Rationale: Motor starting current can be 6× FLC or more, creating significant voltage sag. The existing service
transformer kVA and conductor capacity must be evaluated to ensure the motor can start without dropping voltage below
acceptable limits (typically 5% per NEC 430.7 and utility standards). Brand matching and aesthetic factors are irrelevant to
safe motor installation.
CSLB C-10 Electrical Contractor Exam Preparation - 200 Questions | Based on 2022 California Electrical Code
, C-10 CSLB Electrical Contractor License Exam - Test Bank 2 (2026/2027) Page 4
Q4: During a panel evaluation, the contractor observes aluminum branch-circuit wiring (small-gauge,
single-strand) installed in a 1970s residence. What is the recommended action?
A. Leave the wiring in place; it meets current code if undamaged.
B. Recommend evaluation and repair by a qualified electrician, including application of antioxidant
compound and proper termination per NEC 310.10, or full rewiring. [CORRECT]
C. Replace all breakers with AFCI breakers and consider the system safe.
D. Spray antioxidant on terminations and document as compliant.
Correct Answer: B
Rationale: Single-strand aluminum branch wiring (commonly #12 and #10 AWG) has documented thermal expansion
issues at terminations, creating fire hazards. NEC 310.10 requires proper installation, and CPSC has recommended
evaluation/repair or rewiring. AFCI breakers alone do not address the underlying termination hazard; antioxidant is only
one component of a compliant repair.
Q5: When evaluating an existing grounding electrode system for a service upgrade, the contractor finds a
single ground rod with a measured resistance of 50 ohms. What is required?
A. This meets NEC requirements; no further action is needed.
B. Drive a second ground rod at least 6 feet away, as NEC 250.56 requires supplemental electrode when
resistance exceeds 25 ohms. [CORRECT]
C. Replace the rod with a deeper rod achieving 5 ohms or less.
D. Install a grounding plate instead and abandon the rod.
Correct Answer: B
Rationale: NEC 250.56 requires that a single rod, pipe, or plate electrode with resistance greater than 25 ohms must be
supplemented by an additional electrode. The second rod must be at least 6 feet away per NEC 250.53(A)(3). There is no
requirement to achieve a specific low resistance value when using the two-rod exception.
Q6: A contractor evaluating a 50-year-old industrial facility's switchgear notes visible tracking, carbonized
insulation, and pitting on breaker contacts. What is the appropriate engineering determination?
A. Clean the contacts with emery cloth and re-energize.
B. Specify complete replacement of the affected switchgear section; tracking and carbonization indicate
insulation breakdown that cannot be reliably field-repaired. [CORRECT]
C. Apply dielectric grease and continue service.
D. Lower the trip settings to reduce arc energy.
Correct Answer: B
Rationale: Tracking and carbonization of switchgear insulation indicate irreversible dielectric breakdown that
compromises the insulation system and presents arc-flash and shock hazards. Cleaning or applying grease does not restore
the dielectric strength. Per industry consensus (NFPA 70B and NEMA standards), the affected switchgear must be
replaced.
Q7: When evaluating an existing service for adding solar PV, what is the FIRST consideration regarding the
main service panel?
A. Verify the panel's busbar rating and main breaker size to determine allowable PV backfeed per NEC
705.12(B). [CORRECT]
B. Confirm the panel color matches the PV inverter enclosure.
CSLB C-10 Electrical Contractor Exam Preparation - 200 Questions | Based on 2022 California Electrical Code
CSLB C-10 Electrical Contractor
License Examination
Test Bank 2 — Edition
Real Exam Preparation Questions and Correct Answers
Total Questions: 200 Multiple-Choice Questions
Exam Format: Two separate exams - Trade and Law & Business
Passing Score: 72% (minimum required to pass)
Administration: PSI Testing Centers - Closed Book
Time Limit: Approximately 2.5 hours per exam section
Code Basis: 2022 California Electrical Code (CEC) / NEC 2020
Cognitive Levels: 30% Recall, 50% Application, 20% Analysis
Coverage: Planning, Rough Wiring, Finish, Troubleshooting, Safety
C-10 Classification: Installing, erecting, constructing, repairing, servicing, altering, or designing electrical
wiring, services, equipment, and apparatus for light, heat, and power.
This study guide is designed for exam preparation purposes and reflects 2026/2027 CSLB standards based on
the 2022 California Codes.
CSLB C-10 Electrical Contractor Exam Preparation - 200 Questions | Based on 2022 California Electrical Code
,C-10 CSLB Electrical Contractor License Exam - Test Bank 2 (2026/2027) Page 2
Table of Contents
Section 1: Planning and Estimating Q1 - Q56 28%
Section 2: Rough Wiring Q57 - Q110 27%
Section 3: Finish Wiring and Trim Q111 - Q132 11%
Section 4: Startup, Troubleshooting, and Maintenance Q133 - Q164 16%
Section 5: Safety Q165 - Q200 18%
How to Use This Exam: Each question is followed by four answer choices (A–D), with the correct answer
marked [CORRECT] and the rationale explaining the code reference and reasoning. The minimum passing
score for the actual CSLB exam is 72%.
CSLB C-10 Electrical Contractor Exam Preparation - 200 Questions | Based on 2022 California Electrical Code
,C-10 CSLB Electrical Contractor License Exam - Test Bank 2 (2026/2027) Page 3
SECTION 1: PLANNING AND ESTIMATING
Topics: Existing System Evaluation | Plan Interpretation | Electrical Calculations | Code Requirements
(NEC 210, 220, 240, 250, 310, 314, 430, 690) | Material Selection | Energy Production/Storage Planning
Q1: A contractor is evaluating an existing 1970s residence for a service upgrade. The existing 100-amp panel
uses Federal Pacific Stab-Lok breakers. What is the MOST appropriate recommendation to the homeowner?
A. Add additional breakers as needed; the existing panel can be reused up to 125 amps.
B. Recommend a complete panel replacement with a modern 200-amp service due to documented failure
history of Stab-Lok breakers. [CORRECT]
C. Replace only the failed breakers with after-market equivalents to save cost.
D. Install a subpanel adjacent to the existing panel to expand capacity.
Correct Answer: B
Rationale: Federal Pacific Stab-Lok breakers have a documented history of failure to trip under fault conditions, creating
fire and shock hazards. A complete panel replacement with a modern listed 200-amp service addresses both safety and
capacity for modern loads. Reusing, repairing, or sub-paneling off a known-defective panel violates the C-10 contractor's
duty under NEC 110.3(B) and Cal/OSHA safety expectations.
Q2: When evaluating an existing commercial service for an added EV charging load, what is the FIRST
calculation the contractor must perform?
A. Determine the size of new conductors required to handle the additional load.
B. Perform a load calculation per NEC Article 220 to verify the existing service has spare capacity.
[CORRECT]
C. Select a new main breaker size to accommodate the new load.
D. Specify the wire gauge based on the EV charger nameplate rating only.
Correct Answer: B
Rationale: NEC Article 220 governs load calculations and must be applied to verify existing service capacity before
adding any new load. Adding conductors, breakers, or chargers without an Article 220 evaluation risks overloading the
service and violates NEC 220.1. The nameplate alone is insufficient because demand factors and existing loads must be
considered.
Q3: An existing industrial facility has a 480V three-phase service with a 400-amp main breaker. The facility
wants to add a 100HP motor (FLC 124A). What existing-system factor must be evaluated BEFORE adding
the motor?
A. The color of the existing conduit for proper identification.
B. Whether the existing service and transformer kVA can handle the motor's starting (inrush) current
without voltage sag. [CORRECT]
C. The brand of the existing breakers for matching purposes.
D. The age of the existing grounding electrode conductor.
Correct Answer: B
Rationale: Motor starting current can be 6× FLC or more, creating significant voltage sag. The existing service
transformer kVA and conductor capacity must be evaluated to ensure the motor can start without dropping voltage below
acceptable limits (typically 5% per NEC 430.7 and utility standards). Brand matching and aesthetic factors are irrelevant to
safe motor installation.
CSLB C-10 Electrical Contractor Exam Preparation - 200 Questions | Based on 2022 California Electrical Code
, C-10 CSLB Electrical Contractor License Exam - Test Bank 2 (2026/2027) Page 4
Q4: During a panel evaluation, the contractor observes aluminum branch-circuit wiring (small-gauge,
single-strand) installed in a 1970s residence. What is the recommended action?
A. Leave the wiring in place; it meets current code if undamaged.
B. Recommend evaluation and repair by a qualified electrician, including application of antioxidant
compound and proper termination per NEC 310.10, or full rewiring. [CORRECT]
C. Replace all breakers with AFCI breakers and consider the system safe.
D. Spray antioxidant on terminations and document as compliant.
Correct Answer: B
Rationale: Single-strand aluminum branch wiring (commonly #12 and #10 AWG) has documented thermal expansion
issues at terminations, creating fire hazards. NEC 310.10 requires proper installation, and CPSC has recommended
evaluation/repair or rewiring. AFCI breakers alone do not address the underlying termination hazard; antioxidant is only
one component of a compliant repair.
Q5: When evaluating an existing grounding electrode system for a service upgrade, the contractor finds a
single ground rod with a measured resistance of 50 ohms. What is required?
A. This meets NEC requirements; no further action is needed.
B. Drive a second ground rod at least 6 feet away, as NEC 250.56 requires supplemental electrode when
resistance exceeds 25 ohms. [CORRECT]
C. Replace the rod with a deeper rod achieving 5 ohms or less.
D. Install a grounding plate instead and abandon the rod.
Correct Answer: B
Rationale: NEC 250.56 requires that a single rod, pipe, or plate electrode with resistance greater than 25 ohms must be
supplemented by an additional electrode. The second rod must be at least 6 feet away per NEC 250.53(A)(3). There is no
requirement to achieve a specific low resistance value when using the two-rod exception.
Q6: A contractor evaluating a 50-year-old industrial facility's switchgear notes visible tracking, carbonized
insulation, and pitting on breaker contacts. What is the appropriate engineering determination?
A. Clean the contacts with emery cloth and re-energize.
B. Specify complete replacement of the affected switchgear section; tracking and carbonization indicate
insulation breakdown that cannot be reliably field-repaired. [CORRECT]
C. Apply dielectric grease and continue service.
D. Lower the trip settings to reduce arc energy.
Correct Answer: B
Rationale: Tracking and carbonization of switchgear insulation indicate irreversible dielectric breakdown that
compromises the insulation system and presents arc-flash and shock hazards. Cleaning or applying grease does not restore
the dielectric strength. Per industry consensus (NFPA 70B and NEMA standards), the affected switchgear must be
replaced.
Q7: When evaluating an existing service for adding solar PV, what is the FIRST consideration regarding the
main service panel?
A. Verify the panel's busbar rating and main breaker size to determine allowable PV backfeed per NEC
705.12(B). [CORRECT]
B. Confirm the panel color matches the PV inverter enclosure.
CSLB C-10 Electrical Contractor Exam Preparation - 200 Questions | Based on 2022 California Electrical Code
