CSLB C10 Test 1 | Questions and Verified Answers | Rated A+ | Latest 2026/2027 2026/2027 - 2026/2027 Official Exam
OBJECTIVE ASSESSMENT - EXAM
CSLB C10 Test 1 | Questions and Verified Answers | Rated A+
| Latest 2026/2027 2026/2027 - 2026/2027 Official Exam
75 100% 2026/2027
QUESTIONS VERIFIED ANSWERS EDITION
TOPICS COVERED
Electrical Theory & Applications Safety & OSHA Regulations
National Electrical Code (NEC) California Electrical Contracting Laws
Wiring Methods & Materials
COVER PAGE - 1
, SECTION 1 | Electrical Theory & Applications | Q1-Q15 | CSLB C10 Test 1 | Questions and Verified Answers | Rated A+ |
Latest 2026/2027 2026/2027 - 2026/2027 Official Exam 2026/2027
Q1 Question 1 of 75
A 34-year-old apprentice electrician measures 120 volts across the two hot conductors of a single-phase
residential service and 0 volts between each hot and the grounded neutral. The journeyman asks what this
indicates about the transformer supplying the residence. Which finding is most accurate?
A. The utility transformer secondary has an open neutral
B. The service drop conductors are shorted together
C. The meter base is bypassed and energized
D. The main breaker is locked in the off position
Correct Answer: A
Rationale:
An open neutral on the utility side typically produces abnormal voltage readings between phases and neutral, but zero volts
hot-to-neutral with normal hot-to-hot voltage most often indicates an open or missing neutral reference at the service.
Shorted hots would trip the utility protection, a bypassed meter is unrelated to voltage readings, and a locked breaker would
de-energize everything. The transformer secondary losing its grounded neutral reference best matches the symptom.
Q2 Question 2 of 75
On a 208Y/120-volt three-phase, four-wire system, an electrician connects a single-phase load between one
phase conductor and the neutral. What is the expected voltage across the load under normal operating
conditions?
A. 208 volts
B. 120 volts
C. 277 volts
D. 240 volts
Correct Answer: B
Rationale:
A 208Y/120-volt three-phase four-wire system supplies 120 volts phase-to-neutral and 208 volts phase-to-phase. The
single-phase load connected phase-to-neutral receives 120 volts. 277 volts is associated with 480Y/277 systems and 240
volts with single-phase residential services. The line-to-neutral value of this wye system is 120 volts.
CSLB C10 Test 1 | Questions and Verified Answers | Rated A+ | Latest 2026/2027 2026/2027 - 2026/2027 Official Exam - 2026/2027 | Passing Score: 80% | Page 2 of 41
, Q3 Question 3 of 75
A homeowner reports that lights dim when the refrigerator compressor starts. The electrician knows that
voltage drop on a branch circuit is limited by the National Electrical Code. For most branch circuits, the
recommended maximum voltage drop from service equipment to the furthest outlet is approximately what
percent?
A. 3 percent
B. 5 percent
C. 3 percent
D. 10 percent
Correct Answer: C
Rationale:
The NEC recommends a maximum voltage drop of three percent on branch circuits and five percent total from service to the
farthest outlet, although these are informational notes rather than enforceable rules. Five percent applies to the
feeder-plus-branch total, and ten percent is excessive. The branch-circuit recommendation is three percent.
Q4 Question 4 of 75
An electrician must size a conductor for a continuous load of 24 amperes on a circuit rated at 30 amperes.
The NEC requires conductors and overcurrent devices for continuous loads to be sized at what percentage
of the continuous load?
A. 100 percent
B. 110 percent
C. 115 percent
D. 125 percent
Correct Answer: D
Rationale:
NEC 210.20(A) and 215.2(A)(1) require overcurrent devices and conductors supplying continuous loads to be sized at 125
percent of the continuous load. 100 percent applies to noncontinuous loads, and 110 and 115 percent are not standard NEC
multipliers for continuous load sizing. The 125 percent rule prevents nuisance tripping from sustained current.
CSLB C10 Test 1 | Questions and Verified Answers | Rated A+ | Latest 2026/2027 2026/2027 - 2026/2027 Official Exam - 2026/2027 | Passing Score: 80% | Page 3 of 41
, Q5 Question 5 of 75
An apprentice is studying Ohm's law and must calculate the current drawn by a 12-ohm resistor connected
across a 24-volt source. What current will the resistor carry?
A. 2 amperes
B. 0.5 amperes
C. 288 amperes
D. 12 amperes
Correct Answer: A
Rationale:
Ohm's law states that current equals voltage divided by resistance, so 24 volts divided by 12 ohms yields 2 amperes.
Multiplying voltage and resistance gives the wrong unit, and 288 is the product rather than the quotient. The straightforward
application of I equals V over R gives 2 amperes.
Q6 Question 6 of 75
A circuit has a 20-ampere breaker protecting 12 AWG copper conductors. The journeyman reminds the
apprentice that 12 AWG copper THHN conductors in the 60 degree Celsius column of Table 310.16 have an
ampacity of what value?
A. 15 amperes
B. 20 amperes
C. 25 amperes
D. 30 amperes
Correct Answer: B
Rationale:
Table 310.16 lists 12 AWG copper at 20 amperes in the 60 degree Celsius column, 25 amperes at 75 degrees, and 30
amperes at 90 degrees. The 60 degree column value is used for termination ratings under 110.14(C)(1)(a) for equipment
rated 100 amperes or less. The correct value at 60 degrees is 20 amperes.
CSLB C10 Test 1 | Questions and Verified Answers | Rated A+ | Latest 2026/2027 2026/2027 - 2026/2027 Official Exam - 2026/2027 | Passing Score: 80% | Page 4 of 41
OBJECTIVE ASSESSMENT - EXAM
CSLB C10 Test 1 | Questions and Verified Answers | Rated A+
| Latest 2026/2027 2026/2027 - 2026/2027 Official Exam
75 100% 2026/2027
QUESTIONS VERIFIED ANSWERS EDITION
TOPICS COVERED
Electrical Theory & Applications Safety & OSHA Regulations
National Electrical Code (NEC) California Electrical Contracting Laws
Wiring Methods & Materials
COVER PAGE - 1
, SECTION 1 | Electrical Theory & Applications | Q1-Q15 | CSLB C10 Test 1 | Questions and Verified Answers | Rated A+ |
Latest 2026/2027 2026/2027 - 2026/2027 Official Exam 2026/2027
Q1 Question 1 of 75
A 34-year-old apprentice electrician measures 120 volts across the two hot conductors of a single-phase
residential service and 0 volts between each hot and the grounded neutral. The journeyman asks what this
indicates about the transformer supplying the residence. Which finding is most accurate?
A. The utility transformer secondary has an open neutral
B. The service drop conductors are shorted together
C. The meter base is bypassed and energized
D. The main breaker is locked in the off position
Correct Answer: A
Rationale:
An open neutral on the utility side typically produces abnormal voltage readings between phases and neutral, but zero volts
hot-to-neutral with normal hot-to-hot voltage most often indicates an open or missing neutral reference at the service.
Shorted hots would trip the utility protection, a bypassed meter is unrelated to voltage readings, and a locked breaker would
de-energize everything. The transformer secondary losing its grounded neutral reference best matches the symptom.
Q2 Question 2 of 75
On a 208Y/120-volt three-phase, four-wire system, an electrician connects a single-phase load between one
phase conductor and the neutral. What is the expected voltage across the load under normal operating
conditions?
A. 208 volts
B. 120 volts
C. 277 volts
D. 240 volts
Correct Answer: B
Rationale:
A 208Y/120-volt three-phase four-wire system supplies 120 volts phase-to-neutral and 208 volts phase-to-phase. The
single-phase load connected phase-to-neutral receives 120 volts. 277 volts is associated with 480Y/277 systems and 240
volts with single-phase residential services. The line-to-neutral value of this wye system is 120 volts.
CSLB C10 Test 1 | Questions and Verified Answers | Rated A+ | Latest 2026/2027 2026/2027 - 2026/2027 Official Exam - 2026/2027 | Passing Score: 80% | Page 2 of 41
, Q3 Question 3 of 75
A homeowner reports that lights dim when the refrigerator compressor starts. The electrician knows that
voltage drop on a branch circuit is limited by the National Electrical Code. For most branch circuits, the
recommended maximum voltage drop from service equipment to the furthest outlet is approximately what
percent?
A. 3 percent
B. 5 percent
C. 3 percent
D. 10 percent
Correct Answer: C
Rationale:
The NEC recommends a maximum voltage drop of three percent on branch circuits and five percent total from service to the
farthest outlet, although these are informational notes rather than enforceable rules. Five percent applies to the
feeder-plus-branch total, and ten percent is excessive. The branch-circuit recommendation is three percent.
Q4 Question 4 of 75
An electrician must size a conductor for a continuous load of 24 amperes on a circuit rated at 30 amperes.
The NEC requires conductors and overcurrent devices for continuous loads to be sized at what percentage
of the continuous load?
A. 100 percent
B. 110 percent
C. 115 percent
D. 125 percent
Correct Answer: D
Rationale:
NEC 210.20(A) and 215.2(A)(1) require overcurrent devices and conductors supplying continuous loads to be sized at 125
percent of the continuous load. 100 percent applies to noncontinuous loads, and 110 and 115 percent are not standard NEC
multipliers for continuous load sizing. The 125 percent rule prevents nuisance tripping from sustained current.
CSLB C10 Test 1 | Questions and Verified Answers | Rated A+ | Latest 2026/2027 2026/2027 - 2026/2027 Official Exam - 2026/2027 | Passing Score: 80% | Page 3 of 41
, Q5 Question 5 of 75
An apprentice is studying Ohm's law and must calculate the current drawn by a 12-ohm resistor connected
across a 24-volt source. What current will the resistor carry?
A. 2 amperes
B. 0.5 amperes
C. 288 amperes
D. 12 amperes
Correct Answer: A
Rationale:
Ohm's law states that current equals voltage divided by resistance, so 24 volts divided by 12 ohms yields 2 amperes.
Multiplying voltage and resistance gives the wrong unit, and 288 is the product rather than the quotient. The straightforward
application of I equals V over R gives 2 amperes.
Q6 Question 6 of 75
A circuit has a 20-ampere breaker protecting 12 AWG copper conductors. The journeyman reminds the
apprentice that 12 AWG copper THHN conductors in the 60 degree Celsius column of Table 310.16 have an
ampacity of what value?
A. 15 amperes
B. 20 amperes
C. 25 amperes
D. 30 amperes
Correct Answer: B
Rationale:
Table 310.16 lists 12 AWG copper at 20 amperes in the 60 degree Celsius column, 25 amperes at 75 degrees, and 30
amperes at 90 degrees. The 60 degree column value is used for termination ratings under 110.14(C)(1)(a) for equipment
rated 100 amperes or less. The correct value at 60 degrees is 20 amperes.
CSLB C10 Test 1 | Questions and Verified Answers | Rated A+ | Latest 2026/2027 2026/2027 - 2026/2027 Official Exam - 2026/2027 | Passing Score: 80% | Page 4 of 41
