Motor Controls and Industrial Wiring Exam:
Verified Questions and Answers | Instant PDF
Study Guide
1. What is the primary function of a motor starter in an
industrial control circuit?
A. To increase motor speed above its rated speed
B. To convert AC power into DC power
C. To provide a means of starting, stopping, and protecting the
motor
D. To reduce the motor's horsepower rating
Rationale: A motor starter combines switching and protective
functions to safely control a motor. A typical starter includes a
contactor or motor starter mechanism and overload protection,
allowing the motor to be started and stopped while protecting it
from sustained overload conditions.
2. Which component is primarily responsible for protecting a
motor against sustained overcurrent caused by an overload?
A. Control transformer
B. Pushbutton
C. Overload relay
D. Pilot light
,Rationale: An overload relay monitors motor current and opens
the control circuit when the motor draws excessive current for a
sufficient period. This protects the motor from overheating due
to conditions such as excessive mechanical load or a stalled
motor.
3. What is the purpose of a normally open pushbutton in a
typical motor-start circuit?
A. To disconnect the motor's power circuit permanently
B. To momentarily complete the control circuit when pressed
C. To protect the motor from short circuits
D. To reduce the control voltage
Rationale: A normally open START pushbutton closes its contacts
when pressed. This temporarily energizes the starter coil, which
then typically uses an auxiliary holding contact to maintain the
circuit after the operator releases the button.
4. What type of contact is normally used for a STOP
pushbutton?
A. Normally open
B. Normally closed
C. Double-pole normally open
D. Timed normally open
Rationale: A STOP pushbutton is normally closed so that the
control circuit remains complete during normal operation.
,Pressing the button opens the circuit and de-energizes the
starter coil, stopping the motor.
5. What is the purpose of a seal-in or holding contact in a
motor starter circuit?
A. To reduce motor voltage
B. To provide short-circuit protection
C. To keep the starter coil energized after the START button is
released
D. To reverse the motor's direction
Rationale: The auxiliary holding contact is wired in parallel with
the START pushbutton. Once the contactor coil energizes, the
auxiliary contact closes and provides an alternate current path,
allowing the motor to continue running after the START button is
released.
6. A three-phase motor rotates in the wrong direction. What is
the usual corrective action?
A. Increase the control voltage
B. Replace the overload relay
C. Interchange any two of the three-phase supply conductors
D. Connect the motor to neutral
Rationale: Reversing any two phases changes the phase
sequence reaching a three-phase motor and reverses its
rotational direction. This should only be done with the
, equipment de-energized and according to applicable safety
procedures.
7. What is the primary purpose of a contactor in an industrial
motor control circuit?
A. To measure motor insulation resistance
B. To electrically switch power to the motor
C. To convert three-phase power to single-phase power
D. To provide mechanical lubrication
Rationale: A contactor is an electrically controlled switching
device designed to repeatedly make and break power circuits.
Its coil is controlled by the low-power control circuit while its
main contacts switch the motor's power.
8. Which device is commonly used to provide a lower control
voltage from a higher supply voltage?
A. Overload relay
B. Contactor
C. Control transformer
D. Motor capacitor
Rationale: A control transformer steps voltage up or down to
provide an appropriate control voltage. Using a lower control
voltage can improve safety and allow control components such
as pushbuttons, relays, and coils to operate at their rated
voltage.
Verified Questions and Answers | Instant PDF
Study Guide
1. What is the primary function of a motor starter in an
industrial control circuit?
A. To increase motor speed above its rated speed
B. To convert AC power into DC power
C. To provide a means of starting, stopping, and protecting the
motor
D. To reduce the motor's horsepower rating
Rationale: A motor starter combines switching and protective
functions to safely control a motor. A typical starter includes a
contactor or motor starter mechanism and overload protection,
allowing the motor to be started and stopped while protecting it
from sustained overload conditions.
2. Which component is primarily responsible for protecting a
motor against sustained overcurrent caused by an overload?
A. Control transformer
B. Pushbutton
C. Overload relay
D. Pilot light
,Rationale: An overload relay monitors motor current and opens
the control circuit when the motor draws excessive current for a
sufficient period. This protects the motor from overheating due
to conditions such as excessive mechanical load or a stalled
motor.
3. What is the purpose of a normally open pushbutton in a
typical motor-start circuit?
A. To disconnect the motor's power circuit permanently
B. To momentarily complete the control circuit when pressed
C. To protect the motor from short circuits
D. To reduce the control voltage
Rationale: A normally open START pushbutton closes its contacts
when pressed. This temporarily energizes the starter coil, which
then typically uses an auxiliary holding contact to maintain the
circuit after the operator releases the button.
4. What type of contact is normally used for a STOP
pushbutton?
A. Normally open
B. Normally closed
C. Double-pole normally open
D. Timed normally open
Rationale: A STOP pushbutton is normally closed so that the
control circuit remains complete during normal operation.
,Pressing the button opens the circuit and de-energizes the
starter coil, stopping the motor.
5. What is the purpose of a seal-in or holding contact in a
motor starter circuit?
A. To reduce motor voltage
B. To provide short-circuit protection
C. To keep the starter coil energized after the START button is
released
D. To reverse the motor's direction
Rationale: The auxiliary holding contact is wired in parallel with
the START pushbutton. Once the contactor coil energizes, the
auxiliary contact closes and provides an alternate current path,
allowing the motor to continue running after the START button is
released.
6. A three-phase motor rotates in the wrong direction. What is
the usual corrective action?
A. Increase the control voltage
B. Replace the overload relay
C. Interchange any two of the three-phase supply conductors
D. Connect the motor to neutral
Rationale: Reversing any two phases changes the phase
sequence reaching a three-phase motor and reverses its
rotational direction. This should only be done with the
, equipment de-energized and according to applicable safety
procedures.
7. What is the primary purpose of a contactor in an industrial
motor control circuit?
A. To measure motor insulation resistance
B. To electrically switch power to the motor
C. To convert three-phase power to single-phase power
D. To provide mechanical lubrication
Rationale: A contactor is an electrically controlled switching
device designed to repeatedly make and break power circuits.
Its coil is controlled by the low-power control circuit while its
main contacts switch the motor's power.
8. Which device is commonly used to provide a lower control
voltage from a higher supply voltage?
A. Overload relay
B. Contactor
C. Control transformer
D. Motor capacitor
Rationale: A control transformer steps voltage up or down to
provide an appropriate control voltage. Using a lower control
voltage can improve safety and allow control components such
as pushbuttons, relays, and coils to operate at their rated
voltage.
