C-10 Electrical Contractor CSLB License Exam 2026/2027 | 150 Questions with Correct Answers
C-10 Electrical Contractor CSLB License Test 2026/2027
150 Real Exam Preparation Questions with Correct Answers and Rationales
Multiple Choice (A-D) | CSLB Exam Format | Based on 2026 NEC and California Codes
Section 1: Planning and Estimating (Q1-Q42)
System Evaluation, Plan Interpretation, Electrical Calculations, Code Requirements, Material Selection, and Energy
Production/Storage Planning
Q1: A contractor is planning the branch circuit wiring for a new 2,400 sq ft single-family dwelling. Per NEC 220,
what is the general lighting and receptacle calculated load in volt-amperes before applying any demand factor?
A. 2,400 VA
B. 3,000 VA
C. 7,200 VA [CORRECT]
D. 9,600 VA
Correct Answer: C
Rationale: NEC 220.12 requires a minimum unit load of 3 VA per sq ft for dwelling unit general lighting and receptacle loads.
For a 2,400 sq ft dwelling: 2,400 x 3 = 7,200 VA. This is the calculated load before demand factors per NEC 220.45 are applied.
Option A uses 1 VA/sq ft which is incorrect. Option B is the first-tier demand threshold, not the calculated load. Option D would
require a 4 VA/sq ft rate which applies to hotel/motel guest rooms, not dwelling units.
Q2: Using Ohm's Law, if a 240V circuit feeds a resistive heating element that draws 20 amperes, what is the
resistance of the element?
A. 8 ohms
B. 10 ohms
C. 12 ohms [CORRECT]
D. 48 ohms
Correct Answer: C
Rationale: Ohm's Law: E = I x R, rearranged to R = E / I. Given E = 240V and I = 20A: R = = 12 ohms. Option A (8
ohms) would require 30A at 240V. Option B (10 ohms) would result in 24A at 240V. Option D (48 ohms) would only draw 5A at
240V. Ohm's Law is fundamental to circuit analysis per NEC Chapter 9, Table 8.
Q3: A three-phase 208V wye-connected system supplies a balanced load. What is the phase-to-neutral voltage?
A. 120V [CORRECT]
B. 208V
C. 240V
D. 360V
Correct Answer: A
Page 1
, C-10 Electrical Contractor CSLB License Exam 2026/2027 | 150 Questions with Correct Answers
Rationale: In a three-phase wye system, the line-to-line voltage equals the phase voltage multiplied by the square root of 3
(1.732). Therefore, the phase-to-neutral voltage = line voltage / sqrt(3) = .732 = 120V. Option B is the line-to-line voltage,
not phase-to-neutral. Option C (240V) is the line-to-line voltage of a different common system. Option D (360V) has no
relationship to a 208V wye system. This relationship is fundamental to three-phase system design per NEC Article 210.
Q4: What is the minimum size copper service-entrance conductor required for a single-family dwelling with a
calculated load of 200 amperes at 240V? Use THWN conductors rated 75 degrees C.
A. 2/0 AWG
B. 3/0 AWG
C. 4/0 AWG [CORRECT]
D. 250 kcmil
Correct Answer: C
Rationale: Per NEC Table 310.15(B)(16), under the 75 degree C column for THWN copper conductors: 2/0 AWG = 175A
(insufficient), 3/0 AWG = 200A (meets the minimum exactly), 4/0 AWG = 230A (exceeds requirement). However, NEC 240.4(B)
allows the next standard size up if the calculated load does not correspond to a standard rating. Since 200A is a standard rating
and 3/0 AWG copper at 75C is exactly 200A, 3/0 AWG meets the requirement. But for service-entrance conductors, NEC
310.15(B)(7) permits 4/0 AWG copper for 200A residential services. Under the 2026 NEC, for dwelling unit 120/240V 3-wire
services, 4/0 AWG copper is the standard minimum for 200A service per Table 310.15(B)(7).
Q5: A contractor must determine the conductor size for a 240V single-phase branch circuit supplying a 12kW
electric range in a dwelling unit. Per NEC 220, what is the demand load used for conductor sizing?
A. 8 kW [CORRECT]
B. 9.6 kW
C. 10.8 kW
D. 12 kW
Correct Answer: A
Rationale: Per NEC 220.55 and Table 220.55, for a single electric range with a nameplate rating of 12 kW, Column C applies
for dwellings. Column C allows a demand of 8 kW for a single 12 kW range. This demand factor recognizes that not all elements
operate simultaneously at full capacity. Option B (9.6 kW) would be the demand if the range were rated between 8.75 kW and 12
kW using Column B incorrectly. Option C (10.8 kW) represents 90% of 12 kW which is not the correct method. Option D (12 kW)
is the nameplate rating without applying the demand factor.
Q6: An electrician needs to calculate voltage drop on a 120V branch circuit that is 150 feet from the panel. The
load draws 16A and uses 12 AWG copper (resistance = 1.98 ohms per 1000 ft). What is the approximate voltage
drop?
A. 4.75V [CORRECT]
B. 2.38V
C. 9.50V
D. 11.88V
Correct Answer: A
Page 2
, C-10 Electrical Contractor CSLB License Exam 2026/2027 | 150 Questions with Correct Answers
Rationale: Voltage drop formula: VD = 2 x I x R x L / 1000. For a single-phase circuit, the factor is 2 (out and back). VD = 2 x
16A x (1.98 ohms/1000ft) x 150ft / 1000 = 2 x 16 x 1.98 x 0.15 = 9.504V. As a percentage: 9. x 100 = 7.92%. The
NEC recommends voltage drop not exceed 3% for branch circuits (NEC 215.2(A)(1) FPN and 210.19(A)(1) FPN). At 7.92%,
this exceeds the recommendation, and the conductor should be upsized to 10 AWG. Option B uses only one-way distance. Option C
and D miscalculate the formula.
Q7: Under California contractor law, a C-10 electrical contractor receives a home improvement contract for a
kitchen remodel totaling $3,500. Which of the following is TRUE regarding the 3-day right to cancel?
A. The 3-day right to cancel does not apply because the contract exceeds $500
B. The 3-day right applies only to contracts signed at the contractor's place of business
C. The homeowner has 3 business days to cancel the contract without penalty or obligation [CORRECT]
D. The cancellation period is 5 business days because the work involves electrical modifications
Correct Answer: C
Rationale: California Business and Professions Code Section 7150 et seq. and the Federal Trade Commission's Cooling-Off Rule
provide a 3-business-day right to cancel for home improvement contracts signed at the consumer's residence or any location that is
not the seller's permanent place of business. The $500 threshold means the right applies to contracts of $500 or more. The
contract at $3,500 exceeds this threshold, so the 3-day right to cancel applies. Option A is incorrect because the right DOES apply
when over $500. Option B is incorrect because the right applies when signed AWAY from the seller's place of business, not at it.
Option D is incorrect; 5 days applies to special circumstances like home solicitation sales, not standard home improvement.
Q8: A 5-horsepower, 240V single-phase motor has a full-load current rating of 28 amperes per NEC Table
430.248. What is the minimum ampacity required for the motor branch circuit conductors?
A. 28A
B. 31.4A
C. 35A [CORRECT]
D. 40A
Correct Answer: C
Rationale: Per NEC 430.22, branch circuit conductors supplying a single motor shall have an ampacity not less than 125% of the
motor full-load current (FLC) from Table 430.248. Therefore: 28A x 1.25 = 35A. The FLC from the NEC table is used, not the
nameplate current. Option A uses the FLC directly without the 125% multiplier. Option B (31.4A) appears to use the nameplate
current with 125% factor. Option D (40A) is the next standard size up but is not the minimum required ampacity. Per NEC 240.4,
if the ampacity does not match a standard fuse or breaker size, the next higher standard rating may be used.
Q9: A contractor is reviewing blueprints for a commercial building and finds the electrical plan shows a symbol
with a circle containing the letters 'MCC'. What does this symbol represent?
A. Main Circuit Controller
B. Motor Control Center [CORRECT]
C. Main Current Capacitor
D. Metering Connection Cabinet
Correct Answer: B
Page 3
, C-10 Electrical Contractor CSLB License Exam 2026/2027 | 150 Questions with Correct Answers
Rationale: On electrical construction blueprints, the symbol 'MCC' inside a circle or rectangle represents a Motor Control Center.
An MCC is a floor-mounted assembly of motor starters, protective devices, and control equipment used to control multiple motors
from a central location. This is a standard symbol per NFPA 170 (Standard for Fire Safety and Emergency Symbols) and
common electrical drafting practices. Option A is a fabricated term. Option C combines unrelated electrical components. Option D
describes a metering enclosure, which uses different symbols (typically a circle with 'M' or 'Me').
Q10: Per the California ABC test (AB5), which factor is MOST important in determining whether a worker is an
employee or an independent contractor?
A. Whether the worker provides their own tools and equipment
B. Whether the hiring entity controls the manner and means of the work performed [CORRECT]
C. Whether the worker is paid by the hour or by the project
D. Whether the worker has a valid contractor license
Correct Answer: B
Rationale: Assembly Bill 5 (AB5) codified the ABC test from the California Supreme Court's Dynamex decision (Dynamex
Operations West, Inc. v. Superior Court). Under the ABC test, a worker is presumed to be an employee unless the hiring entity
demonstrates all three prongs: (A) the worker is free from control and direction in performing the work, (B) the work is outside
the usual course of the hiring entity's business, and (C) the worker is customarily engaged in an independently established trade.
Prong A (control) is the most fundamental factor. Having a contractor license does not automatically make someone an
independent contractor. Tool ownership and payment method are secondary considerations, not the primary test.
Q11: A contractor is sizing a grounding electrode conductor for a 200A service with a 4/0 AWG copper
ungrounded service-entrance conductor. What is the minimum size copper grounding electrode conductor required
per NEC 250.66?
A. 6 AWG
B. 4 AWG [CORRECT]
C. 2 AWG
D. 1/0 AWG
Correct Answer: B
Rationale: Per NEC Table 250.66, the grounding electrode conductor (GEC) size is based on the largest ungrounded
service-entrance conductor. For 4/0 AWG copper (or 250 kcmil aluminum), the minimum copper GEC is 4 AWG. Option A (6
AWG) is only sufficient when the largest ungrounded conductor is 2 AWG copper or less. Option C (2 AWG) is required when the
largest ungrounded conductor is over 4/0 AWG up to 350 kcmil copper. Option D (1/0 AWG) is required for conductors larger
than 350 kcmil up to 600 kcmil. The GEC connection to the electrode must also comply with NEC 250.64.
Q12: A three-phase delta-connected system has a phase current of 30 amperes. What is the line current?
A. 17.3A
B. 25.9A
C. 30A
D. 51.96A [CORRECT]
Correct Answer: D
Page 4
C-10 Electrical Contractor CSLB License Test 2026/2027
150 Real Exam Preparation Questions with Correct Answers and Rationales
Multiple Choice (A-D) | CSLB Exam Format | Based on 2026 NEC and California Codes
Section 1: Planning and Estimating (Q1-Q42)
System Evaluation, Plan Interpretation, Electrical Calculations, Code Requirements, Material Selection, and Energy
Production/Storage Planning
Q1: A contractor is planning the branch circuit wiring for a new 2,400 sq ft single-family dwelling. Per NEC 220,
what is the general lighting and receptacle calculated load in volt-amperes before applying any demand factor?
A. 2,400 VA
B. 3,000 VA
C. 7,200 VA [CORRECT]
D. 9,600 VA
Correct Answer: C
Rationale: NEC 220.12 requires a minimum unit load of 3 VA per sq ft for dwelling unit general lighting and receptacle loads.
For a 2,400 sq ft dwelling: 2,400 x 3 = 7,200 VA. This is the calculated load before demand factors per NEC 220.45 are applied.
Option A uses 1 VA/sq ft which is incorrect. Option B is the first-tier demand threshold, not the calculated load. Option D would
require a 4 VA/sq ft rate which applies to hotel/motel guest rooms, not dwelling units.
Q2: Using Ohm's Law, if a 240V circuit feeds a resistive heating element that draws 20 amperes, what is the
resistance of the element?
A. 8 ohms
B. 10 ohms
C. 12 ohms [CORRECT]
D. 48 ohms
Correct Answer: C
Rationale: Ohm's Law: E = I x R, rearranged to R = E / I. Given E = 240V and I = 20A: R = = 12 ohms. Option A (8
ohms) would require 30A at 240V. Option B (10 ohms) would result in 24A at 240V. Option D (48 ohms) would only draw 5A at
240V. Ohm's Law is fundamental to circuit analysis per NEC Chapter 9, Table 8.
Q3: A three-phase 208V wye-connected system supplies a balanced load. What is the phase-to-neutral voltage?
A. 120V [CORRECT]
B. 208V
C. 240V
D. 360V
Correct Answer: A
Page 1
, C-10 Electrical Contractor CSLB License Exam 2026/2027 | 150 Questions with Correct Answers
Rationale: In a three-phase wye system, the line-to-line voltage equals the phase voltage multiplied by the square root of 3
(1.732). Therefore, the phase-to-neutral voltage = line voltage / sqrt(3) = .732 = 120V. Option B is the line-to-line voltage,
not phase-to-neutral. Option C (240V) is the line-to-line voltage of a different common system. Option D (360V) has no
relationship to a 208V wye system. This relationship is fundamental to three-phase system design per NEC Article 210.
Q4: What is the minimum size copper service-entrance conductor required for a single-family dwelling with a
calculated load of 200 amperes at 240V? Use THWN conductors rated 75 degrees C.
A. 2/0 AWG
B. 3/0 AWG
C. 4/0 AWG [CORRECT]
D. 250 kcmil
Correct Answer: C
Rationale: Per NEC Table 310.15(B)(16), under the 75 degree C column for THWN copper conductors: 2/0 AWG = 175A
(insufficient), 3/0 AWG = 200A (meets the minimum exactly), 4/0 AWG = 230A (exceeds requirement). However, NEC 240.4(B)
allows the next standard size up if the calculated load does not correspond to a standard rating. Since 200A is a standard rating
and 3/0 AWG copper at 75C is exactly 200A, 3/0 AWG meets the requirement. But for service-entrance conductors, NEC
310.15(B)(7) permits 4/0 AWG copper for 200A residential services. Under the 2026 NEC, for dwelling unit 120/240V 3-wire
services, 4/0 AWG copper is the standard minimum for 200A service per Table 310.15(B)(7).
Q5: A contractor must determine the conductor size for a 240V single-phase branch circuit supplying a 12kW
electric range in a dwelling unit. Per NEC 220, what is the demand load used for conductor sizing?
A. 8 kW [CORRECT]
B. 9.6 kW
C. 10.8 kW
D. 12 kW
Correct Answer: A
Rationale: Per NEC 220.55 and Table 220.55, for a single electric range with a nameplate rating of 12 kW, Column C applies
for dwellings. Column C allows a demand of 8 kW for a single 12 kW range. This demand factor recognizes that not all elements
operate simultaneously at full capacity. Option B (9.6 kW) would be the demand if the range were rated between 8.75 kW and 12
kW using Column B incorrectly. Option C (10.8 kW) represents 90% of 12 kW which is not the correct method. Option D (12 kW)
is the nameplate rating without applying the demand factor.
Q6: An electrician needs to calculate voltage drop on a 120V branch circuit that is 150 feet from the panel. The
load draws 16A and uses 12 AWG copper (resistance = 1.98 ohms per 1000 ft). What is the approximate voltage
drop?
A. 4.75V [CORRECT]
B. 2.38V
C. 9.50V
D. 11.88V
Correct Answer: A
Page 2
, C-10 Electrical Contractor CSLB License Exam 2026/2027 | 150 Questions with Correct Answers
Rationale: Voltage drop formula: VD = 2 x I x R x L / 1000. For a single-phase circuit, the factor is 2 (out and back). VD = 2 x
16A x (1.98 ohms/1000ft) x 150ft / 1000 = 2 x 16 x 1.98 x 0.15 = 9.504V. As a percentage: 9. x 100 = 7.92%. The
NEC recommends voltage drop not exceed 3% for branch circuits (NEC 215.2(A)(1) FPN and 210.19(A)(1) FPN). At 7.92%,
this exceeds the recommendation, and the conductor should be upsized to 10 AWG. Option B uses only one-way distance. Option C
and D miscalculate the formula.
Q7: Under California contractor law, a C-10 electrical contractor receives a home improvement contract for a
kitchen remodel totaling $3,500. Which of the following is TRUE regarding the 3-day right to cancel?
A. The 3-day right to cancel does not apply because the contract exceeds $500
B. The 3-day right applies only to contracts signed at the contractor's place of business
C. The homeowner has 3 business days to cancel the contract without penalty or obligation [CORRECT]
D. The cancellation period is 5 business days because the work involves electrical modifications
Correct Answer: C
Rationale: California Business and Professions Code Section 7150 et seq. and the Federal Trade Commission's Cooling-Off Rule
provide a 3-business-day right to cancel for home improvement contracts signed at the consumer's residence or any location that is
not the seller's permanent place of business. The $500 threshold means the right applies to contracts of $500 or more. The
contract at $3,500 exceeds this threshold, so the 3-day right to cancel applies. Option A is incorrect because the right DOES apply
when over $500. Option B is incorrect because the right applies when signed AWAY from the seller's place of business, not at it.
Option D is incorrect; 5 days applies to special circumstances like home solicitation sales, not standard home improvement.
Q8: A 5-horsepower, 240V single-phase motor has a full-load current rating of 28 amperes per NEC Table
430.248. What is the minimum ampacity required for the motor branch circuit conductors?
A. 28A
B. 31.4A
C. 35A [CORRECT]
D. 40A
Correct Answer: C
Rationale: Per NEC 430.22, branch circuit conductors supplying a single motor shall have an ampacity not less than 125% of the
motor full-load current (FLC) from Table 430.248. Therefore: 28A x 1.25 = 35A. The FLC from the NEC table is used, not the
nameplate current. Option A uses the FLC directly without the 125% multiplier. Option B (31.4A) appears to use the nameplate
current with 125% factor. Option D (40A) is the next standard size up but is not the minimum required ampacity. Per NEC 240.4,
if the ampacity does not match a standard fuse or breaker size, the next higher standard rating may be used.
Q9: A contractor is reviewing blueprints for a commercial building and finds the electrical plan shows a symbol
with a circle containing the letters 'MCC'. What does this symbol represent?
A. Main Circuit Controller
B. Motor Control Center [CORRECT]
C. Main Current Capacitor
D. Metering Connection Cabinet
Correct Answer: B
Page 3
, C-10 Electrical Contractor CSLB License Exam 2026/2027 | 150 Questions with Correct Answers
Rationale: On electrical construction blueprints, the symbol 'MCC' inside a circle or rectangle represents a Motor Control Center.
An MCC is a floor-mounted assembly of motor starters, protective devices, and control equipment used to control multiple motors
from a central location. This is a standard symbol per NFPA 170 (Standard for Fire Safety and Emergency Symbols) and
common electrical drafting practices. Option A is a fabricated term. Option C combines unrelated electrical components. Option D
describes a metering enclosure, which uses different symbols (typically a circle with 'M' or 'Me').
Q10: Per the California ABC test (AB5), which factor is MOST important in determining whether a worker is an
employee or an independent contractor?
A. Whether the worker provides their own tools and equipment
B. Whether the hiring entity controls the manner and means of the work performed [CORRECT]
C. Whether the worker is paid by the hour or by the project
D. Whether the worker has a valid contractor license
Correct Answer: B
Rationale: Assembly Bill 5 (AB5) codified the ABC test from the California Supreme Court's Dynamex decision (Dynamex
Operations West, Inc. v. Superior Court). Under the ABC test, a worker is presumed to be an employee unless the hiring entity
demonstrates all three prongs: (A) the worker is free from control and direction in performing the work, (B) the work is outside
the usual course of the hiring entity's business, and (C) the worker is customarily engaged in an independently established trade.
Prong A (control) is the most fundamental factor. Having a contractor license does not automatically make someone an
independent contractor. Tool ownership and payment method are secondary considerations, not the primary test.
Q11: A contractor is sizing a grounding electrode conductor for a 200A service with a 4/0 AWG copper
ungrounded service-entrance conductor. What is the minimum size copper grounding electrode conductor required
per NEC 250.66?
A. 6 AWG
B. 4 AWG [CORRECT]
C. 2 AWG
D. 1/0 AWG
Correct Answer: B
Rationale: Per NEC Table 250.66, the grounding electrode conductor (GEC) size is based on the largest ungrounded
service-entrance conductor. For 4/0 AWG copper (or 250 kcmil aluminum), the minimum copper GEC is 4 AWG. Option A (6
AWG) is only sufficient when the largest ungrounded conductor is 2 AWG copper or less. Option C (2 AWG) is required when the
largest ungrounded conductor is over 4/0 AWG up to 350 kcmil copper. Option D (1/0 AWG) is required for conductors larger
than 350 kcmil up to 600 kcmil. The GEC connection to the electrode must also comply with NEC 250.64.
Q12: A three-phase delta-connected system has a phase current of 30 amperes. What is the line current?
A. 17.3A
B. 25.9A
C. 30A
D. 51.96A [CORRECT]
Correct Answer: D
Page 4
