CSLB C10 Test 1 Actual 2026/2027 – 100%
Verified | Detailed Rationales – Pass
Guaranteed – A+ Graded
Content Area Overview: This actual examination reflects the comprehensive trade knowledge and
practical skills required for success on the CSLB C-10 Electrical Contractor Test 1. It is designed to
evaluate the candidate's ability to plan and estimate electrical projects, perform rough wiring, complete
finish wiring, troubleshoot electrical systems, and maintain job site safety. Questions are structured to
assess recall of code requirements, application of electrical calculations, and analysis of real-world
installation scenarios. This authentic question bank represents the style and content of actual CSLB C-10
exams and serves as a comprehensive resource for candidates demonstrating mastery of electrical
contracting knowledge.
SECTION 1: PLANNING & ESTIMATING (14 Questions)
Q1. A contractor is reviewing plans for a new commercial building. The specifications call for a 400-
ampere service with a 208Y/120V three-phase supply. Which factor is most important when selecting
the service entrance conductors?
A. The color of the conductor insulation
B. The ampacity of the conductors must be sufficient for the calculated load per Article 220 and properly
sized per Article 310 [CORRECT]
C. The conductor length only
D. The brand name of the conductor manufacturer
Rationale: The best answer is B. Service entrance conductors must be sized based on the calculated load
using Article 220 (Branch-Circuit, Feeder, and Service Load Calculations) and then selected from the
appropriate ampacity tables in Article 310 (Conductors for General Wiring). You can't just pick a wire
size based on the service rating—you have to do the math. Conductor color, length (though voltage drop
matters), and brand name are secondary considerations to proper ampacity and code compliance.
Correct Answer: B
,Q2. A residential project requires a load calculation for a 2,500 square foot single-family dwelling. The
general lighting load is calculated at 3 volt-amperes per square foot per NEC Article 220. What is the
general lighting load in volt-amperes?
A. 625 VA
B. 833 VA
C. 7,500 VA [CORRECT]
D. 12,500 VA
Rationale: The best answer is C. The general lighting load is calculated by multiplying the square footage
by 3 VA per square foot: 2,500 × 3 = 7,500 VA. This is the starting point for residential load calculations
per NEC 220.12. The first 3,000 VA is taken at 100%, and the remainder is subject to demand factors per
220.42. Getting this base calculation wrong throws off the entire service sizing, so it's critical to know
this fundamental step.
Correct Answer: C
Q3. A contractor is planning a photovoltaic system installation on a commercial roof. The plans show the
array will produce 50 kW DC. Which NEC article primarily governs the installation of solar photovoltaic
systems?
A. Article 230
B. Article 250
C. Article 690 [CORRECT]
D. Article 760
Rationale: The best answer is C. Article 690 (Solar Photovoltaic Systems) is the primary article in the NEC
that covers the installation of PV systems, including circuit requirements, wiring methods, grounding,
disconnecting means, and marking. Article 230 covers services, Article 250 covers grounding and
bonding in general, and Article 760 covers fire alarm systems. For any solar project, Article 690 is your
go-to reference.
Correct Answer: C
Q4. A project requires installing a feeder to a subpanel 150 feet from the main panel. The calculated
load is 80 amperes at 240 volts. The contractor is concerned about voltage drop. Which guideline is
most commonly applied for maximum allowable voltage drop in feeders?
A. 1%
B. 3% [CORRECT]
, C. 5%
D. 10%
Rationale: The best answer is B. While the NEC doesn't explicitly mandate voltage drop limits as a code
requirement (it's in the Fine Print Notes of 210.19 and 215.2), the standard industry practice and
recommendation is 3% maximum for feeders and 5% total for feeders plus branch circuits combined.
Excessive voltage drop causes equipment to run inefficiently, motors to overheat, and lights to dim. For
a 150-foot run at 80 amps, you'd definitely want to calculate voltage drop and possibly upsize the
conductor to stay within this guideline.
Correct Answer: B
Q5. A contractor is selecting conduit for a wet location exposed to sunlight. Which conduit type is most
appropriate?
A. EMT (Electrical Metallic Tubing)
B. Rigid PVC Conduit, Schedule 40 [CORRECT]
C. Flexible Metal Conduit (FMC)
D. Liquidtight Flexible Metal Conduit (LFMC) without UV rating
Rationale: The best answer is B. Rigid PVC Conduit, Schedule 40 is rated for direct burial and wet
locations, and when it's the sunlight-resistant type, it's suitable for outdoor exposed installations. EMT is
not permitted in wet locations unless all supports, fittings, and enclosures are identified for the purpose.
FMC is not permitted in wet locations at all. LFMC can be used in wet locations but must be specifically
rated for UV exposure if installed in sunlight—standard LFMC without that rating would degrade.
Correct Answer: B
Q6. A contractor is estimating materials for a 200-ampere residential service. The NEC requires a
minimum size for the grounding electrode conductor connected to a concrete-encased electrode (Ufer
ground). What is the minimum size copper grounding electrode conductor for this installation?
A. 8 AWG
B. 6 AWG
C. 4 AWG [CORRECT]
D. 2 AWG
Rationale: The best answer is C. Per NEC Table 250.66, the minimum size for a grounding electrode
conductor connected to a concrete-encased electrode is 4 AWG copper. This is one of those code
requirements you just need to know—there's no calculation shortcut. The concrete-encased electrode
Verified | Detailed Rationales – Pass
Guaranteed – A+ Graded
Content Area Overview: This actual examination reflects the comprehensive trade knowledge and
practical skills required for success on the CSLB C-10 Electrical Contractor Test 1. It is designed to
evaluate the candidate's ability to plan and estimate electrical projects, perform rough wiring, complete
finish wiring, troubleshoot electrical systems, and maintain job site safety. Questions are structured to
assess recall of code requirements, application of electrical calculations, and analysis of real-world
installation scenarios. This authentic question bank represents the style and content of actual CSLB C-10
exams and serves as a comprehensive resource for candidates demonstrating mastery of electrical
contracting knowledge.
SECTION 1: PLANNING & ESTIMATING (14 Questions)
Q1. A contractor is reviewing plans for a new commercial building. The specifications call for a 400-
ampere service with a 208Y/120V three-phase supply. Which factor is most important when selecting
the service entrance conductors?
A. The color of the conductor insulation
B. The ampacity of the conductors must be sufficient for the calculated load per Article 220 and properly
sized per Article 310 [CORRECT]
C. The conductor length only
D. The brand name of the conductor manufacturer
Rationale: The best answer is B. Service entrance conductors must be sized based on the calculated load
using Article 220 (Branch-Circuit, Feeder, and Service Load Calculations) and then selected from the
appropriate ampacity tables in Article 310 (Conductors for General Wiring). You can't just pick a wire
size based on the service rating—you have to do the math. Conductor color, length (though voltage drop
matters), and brand name are secondary considerations to proper ampacity and code compliance.
Correct Answer: B
,Q2. A residential project requires a load calculation for a 2,500 square foot single-family dwelling. The
general lighting load is calculated at 3 volt-amperes per square foot per NEC Article 220. What is the
general lighting load in volt-amperes?
A. 625 VA
B. 833 VA
C. 7,500 VA [CORRECT]
D. 12,500 VA
Rationale: The best answer is C. The general lighting load is calculated by multiplying the square footage
by 3 VA per square foot: 2,500 × 3 = 7,500 VA. This is the starting point for residential load calculations
per NEC 220.12. The first 3,000 VA is taken at 100%, and the remainder is subject to demand factors per
220.42. Getting this base calculation wrong throws off the entire service sizing, so it's critical to know
this fundamental step.
Correct Answer: C
Q3. A contractor is planning a photovoltaic system installation on a commercial roof. The plans show the
array will produce 50 kW DC. Which NEC article primarily governs the installation of solar photovoltaic
systems?
A. Article 230
B. Article 250
C. Article 690 [CORRECT]
D. Article 760
Rationale: The best answer is C. Article 690 (Solar Photovoltaic Systems) is the primary article in the NEC
that covers the installation of PV systems, including circuit requirements, wiring methods, grounding,
disconnecting means, and marking. Article 230 covers services, Article 250 covers grounding and
bonding in general, and Article 760 covers fire alarm systems. For any solar project, Article 690 is your
go-to reference.
Correct Answer: C
Q4. A project requires installing a feeder to a subpanel 150 feet from the main panel. The calculated
load is 80 amperes at 240 volts. The contractor is concerned about voltage drop. Which guideline is
most commonly applied for maximum allowable voltage drop in feeders?
A. 1%
B. 3% [CORRECT]
, C. 5%
D. 10%
Rationale: The best answer is B. While the NEC doesn't explicitly mandate voltage drop limits as a code
requirement (it's in the Fine Print Notes of 210.19 and 215.2), the standard industry practice and
recommendation is 3% maximum for feeders and 5% total for feeders plus branch circuits combined.
Excessive voltage drop causes equipment to run inefficiently, motors to overheat, and lights to dim. For
a 150-foot run at 80 amps, you'd definitely want to calculate voltage drop and possibly upsize the
conductor to stay within this guideline.
Correct Answer: B
Q5. A contractor is selecting conduit for a wet location exposed to sunlight. Which conduit type is most
appropriate?
A. EMT (Electrical Metallic Tubing)
B. Rigid PVC Conduit, Schedule 40 [CORRECT]
C. Flexible Metal Conduit (FMC)
D. Liquidtight Flexible Metal Conduit (LFMC) without UV rating
Rationale: The best answer is B. Rigid PVC Conduit, Schedule 40 is rated for direct burial and wet
locations, and when it's the sunlight-resistant type, it's suitable for outdoor exposed installations. EMT is
not permitted in wet locations unless all supports, fittings, and enclosures are identified for the purpose.
FMC is not permitted in wet locations at all. LFMC can be used in wet locations but must be specifically
rated for UV exposure if installed in sunlight—standard LFMC without that rating would degrade.
Correct Answer: B
Q6. A contractor is estimating materials for a 200-ampere residential service. The NEC requires a
minimum size for the grounding electrode conductor connected to a concrete-encased electrode (Ufer
ground). What is the minimum size copper grounding electrode conductor for this installation?
A. 8 AWG
B. 6 AWG
C. 4 AWG [CORRECT]
D. 2 AWG
Rationale: The best answer is C. Per NEC Table 250.66, the minimum size for a grounding electrode
conductor connected to a concrete-encased electrode is 4 AWG copper. This is one of those code
requirements you just need to know—there's no calculation shortcut. The concrete-encased electrode
