NCCER 26410-20 MOTOR OPERATION AND MAINTENANCE EXAM – QUESTIONS AND ANSWERS | VERIFIED AND
WELL DETAILED ANSWERS | PLUS RATIONALES | GUARANTEED PASS | LATEST EXAM UPDATE
Core Domains
Motor Theory and Operation
Motor Installation and Commissioning
Motor Maintenance and Inspection Procedures
Motor Bearing Maintenance and Analysis
Motor Insulation Testing and Evaluation
Motor Troubleshooting and Diagnostics
Motor Starting Methods and Circuits
Motor Storage and Preservation
Motor Safety and Lifting Procedures
Motor Coupling and Alignment
Introduction
This comprehensive assessment is designed to evaluate a candidate's knowledge and practical skills related to the
operation, maintenance, and troubleshooting of electric motors, as outlined in the NCCER 26410-20 curriculum. The
exam covers a wide range of topics, from foundational motor theory and insulation classes to advanced diagnostic
techniques and preventive maintenance procedures. It emphasizes the practical application of knowledge required for
safe and effective motor care in industrial and commercial settings. The questions are presented in a multiple-choice
format, featuring both direct knowledge-based items and scenario-based questions that test critical thinking and
professional decision-making. Successful completion of this exam demonstrates a thorough understanding of the
principles and practices necessary to ensure the reliable and efficient operation of electric motors, minimizing
downtime and extending motor life. This assessment prioritizes real-world application, requiring the test-taker to make
sound professional judgments based on industry standards and safety protocols.
,Question 1
Which of the following best describes the condition known as single-phasing in a three-phase motor?
A. All three phases are experiencing an overload condition.
B. Two of the power legs are shorted together.
C. One of the legs of a three-phase power source is lost.
D. The voltage in all three phases is severely unbalanced.
🟢 Correct Answer: C. One of the legs of a three-phase power source is lost.
🔴 Explanation: Single-phasing occurs when one phase of a three-phase power supply is lost. This causes the motor
to run on the remaining two phases, which can lead to rapid overheating and failure of the motor windings.
Question 2
Under NEMA usual service conditions, what is the maximum allowable frequency deviation from the motor
nameplate frequency?
A. 1%
B. 5%
C. 10%
D. 15%
🟢 Correct Answer: C. 10%
🔴 Explanation: NEMA usual service conditions permit a frequency variation of not more than 10% of the nameplate
frequency. It is a common mistake to think this is 5%, but NEMA specifies 10%.
Question 3
A turn-to-turn short in a motor winding can be caused by contamination inside the motor casing.
A. True
B. False
🟢 Correct Answer: A. True
,🔴 Explanation: Contamination such as dirt, dust, or moisture inside the motor casing can compromise the
insulation between adjacent turns of a winding, leading to a turn-to-turn short.
Question 4
If the load connected to a motor is increased beyond its rated capacity, which of the following is the most likely
consequence?
A. A decrease in the motor's operating temperature.
B. An increase in the motor's speed and efficiency.
C. Increased operating temperature and decreased motor life.
D. No significant effect if the motor is properly cooled.
🟢 Correct Answer: C. Increased operating temperature and decreased motor life.
🔴 Explanation: Overloading a motor causes it to draw excessive current, which generates more heat than the motor
can dissipate. This elevated operating temperature degrades the insulation and significantly shortens the motor's
service life.
Question 5
Motors with two separate winding circuits typically employ which starting method?
A. Autotransformer starting
B. Wye-delta starting
C. Part-winding starting
D. Resistor starting
🟢 Correct Answer: C. Part-winding starting
🔴 Explanation: Part-winding starting is used on motors with two separate and parallel winding circuits per phase. It
reduces starting current by first energizing one circuit and then, after a time delay, energizing the second circuit.
Question 6
What is the limiting temperature for a Class F insulation system?
A. 105°C
, B. 130°C
C. 155°C
D. 180°C
🟢 Correct Answer: C. 155°C
🔴 Explanation: Class F insulation systems have a thermal endurance suitable for operation at a limiting temperature
of 155°C. This is a standard classification defined by NEMA for insulation systems.
Question 7
Which material are you likely to find in a Class A insulation system?
A. Mica
B. Silicone elastomer
C. Cotton
D. Asbestos
🟢 Correct Answer: C. Cotton
🔴 Explanation: Class A insulation systems typically use materials like cotton, silk, and paper, which are organic in
nature. Their thermal limit is lower than that of other classes like B, F, or H.
Question 8
Which type of totally enclosed motor is equipped with fins to aid in cooling?
A. Totally enclosed, non-ventilated (TENV)
B. Totally enclosed, fan-cooled (TEFC)
C. Totally enclosed, air-over (TEAO)
D. Explosion-proof (XP)
🟢 Correct Answer: B. Totally enclosed, fan-cooled (TEFC)
🔴 Explanation: A TEFC motor has an external fan mounted on the shaft that blows air over the frame, which is
equipped with cooling fins to dissipate heat. This design makes it one of the most common types in industrial
applications.
WELL DETAILED ANSWERS | PLUS RATIONALES | GUARANTEED PASS | LATEST EXAM UPDATE
Core Domains
Motor Theory and Operation
Motor Installation and Commissioning
Motor Maintenance and Inspection Procedures
Motor Bearing Maintenance and Analysis
Motor Insulation Testing and Evaluation
Motor Troubleshooting and Diagnostics
Motor Starting Methods and Circuits
Motor Storage and Preservation
Motor Safety and Lifting Procedures
Motor Coupling and Alignment
Introduction
This comprehensive assessment is designed to evaluate a candidate's knowledge and practical skills related to the
operation, maintenance, and troubleshooting of electric motors, as outlined in the NCCER 26410-20 curriculum. The
exam covers a wide range of topics, from foundational motor theory and insulation classes to advanced diagnostic
techniques and preventive maintenance procedures. It emphasizes the practical application of knowledge required for
safe and effective motor care in industrial and commercial settings. The questions are presented in a multiple-choice
format, featuring both direct knowledge-based items and scenario-based questions that test critical thinking and
professional decision-making. Successful completion of this exam demonstrates a thorough understanding of the
principles and practices necessary to ensure the reliable and efficient operation of electric motors, minimizing
downtime and extending motor life. This assessment prioritizes real-world application, requiring the test-taker to make
sound professional judgments based on industry standards and safety protocols.
,Question 1
Which of the following best describes the condition known as single-phasing in a three-phase motor?
A. All three phases are experiencing an overload condition.
B. Two of the power legs are shorted together.
C. One of the legs of a three-phase power source is lost.
D. The voltage in all three phases is severely unbalanced.
🟢 Correct Answer: C. One of the legs of a three-phase power source is lost.
🔴 Explanation: Single-phasing occurs when one phase of a three-phase power supply is lost. This causes the motor
to run on the remaining two phases, which can lead to rapid overheating and failure of the motor windings.
Question 2
Under NEMA usual service conditions, what is the maximum allowable frequency deviation from the motor
nameplate frequency?
A. 1%
B. 5%
C. 10%
D. 15%
🟢 Correct Answer: C. 10%
🔴 Explanation: NEMA usual service conditions permit a frequency variation of not more than 10% of the nameplate
frequency. It is a common mistake to think this is 5%, but NEMA specifies 10%.
Question 3
A turn-to-turn short in a motor winding can be caused by contamination inside the motor casing.
A. True
B. False
🟢 Correct Answer: A. True
,🔴 Explanation: Contamination such as dirt, dust, or moisture inside the motor casing can compromise the
insulation between adjacent turns of a winding, leading to a turn-to-turn short.
Question 4
If the load connected to a motor is increased beyond its rated capacity, which of the following is the most likely
consequence?
A. A decrease in the motor's operating temperature.
B. An increase in the motor's speed and efficiency.
C. Increased operating temperature and decreased motor life.
D. No significant effect if the motor is properly cooled.
🟢 Correct Answer: C. Increased operating temperature and decreased motor life.
🔴 Explanation: Overloading a motor causes it to draw excessive current, which generates more heat than the motor
can dissipate. This elevated operating temperature degrades the insulation and significantly shortens the motor's
service life.
Question 5
Motors with two separate winding circuits typically employ which starting method?
A. Autotransformer starting
B. Wye-delta starting
C. Part-winding starting
D. Resistor starting
🟢 Correct Answer: C. Part-winding starting
🔴 Explanation: Part-winding starting is used on motors with two separate and parallel winding circuits per phase. It
reduces starting current by first energizing one circuit and then, after a time delay, energizing the second circuit.
Question 6
What is the limiting temperature for a Class F insulation system?
A. 105°C
, B. 130°C
C. 155°C
D. 180°C
🟢 Correct Answer: C. 155°C
🔴 Explanation: Class F insulation systems have a thermal endurance suitable for operation at a limiting temperature
of 155°C. This is a standard classification defined by NEMA for insulation systems.
Question 7
Which material are you likely to find in a Class A insulation system?
A. Mica
B. Silicone elastomer
C. Cotton
D. Asbestos
🟢 Correct Answer: C. Cotton
🔴 Explanation: Class A insulation systems typically use materials like cotton, silk, and paper, which are organic in
nature. Their thermal limit is lower than that of other classes like B, F, or H.
Question 8
Which type of totally enclosed motor is equipped with fins to aid in cooling?
A. Totally enclosed, non-ventilated (TENV)
B. Totally enclosed, fan-cooled (TEFC)
C. Totally enclosed, air-over (TEAO)
D. Explosion-proof (XP)
🟢 Correct Answer: B. Totally enclosed, fan-cooled (TEFC)
🔴 Explanation: A TEFC motor has an external fan mounted on the shaft that blows air over the frame, which is
equipped with cooling fins to dissipate heat. This design makes it one of the most common types in industrial
applications.
