SELF TEST ON CIRCUITS

Electrical Engineering Electrical Machines
1

Questions
Using the following diagram, answer questions 1 to 5:

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  1. Which letter identifies the component that normally provides overcurrent protection for the
    motor branch circuit?

  2. Which letter identifies the component that normally provides overload protection for the
    motor branch circuit?

  3. When energized by the control circuit, which letter identifies the component that provides
    normal starting and stopping actions?

  4. Between which two letters is the control circuit power normally taken from?

  5. Which letter(s) identify devices that must be horsepower rated?

  6. The minimum number of control circuit conductors to a stop/forward/reverse pushbutton
    station that provides low-voltage protection for a three-phase reversible motor is:
    A. 2 wires
    B. 3 wires
    C. 4 wires
    D. 6 wires

  7. Inching is another term used for:
    A. Jogging
    B. Plugging
    C. Shunting
    D. Hunting

  8. The rotation of an AC three-phase induction motor may be reversed by interchanging:
    A. The control circuit
    B. The forward/reverse interlocks
    C. The forward reverse coils
    D. Any two power lines
    Basic Motor Control 155

  9. In a control schematic, a dotted line between two coils generally means that the two coils:
    A. Are operated together
    B. Are mechanically interlocked
    C. Are electrically interlocked
    D. Have a common set of contacts

  10. The purpose of electrical interlocking in a three-phase reversing AC magnetic motor starter is
    to:
    A. Ensure that the forward direction of rotation is selected first
    B. Allow both coils to be energized together
    C. Prevent both coils from being energized simultaneously
    D. Maintain the coil circuit after the stop button is released

  11. To connect a motor solely for jogging operation, the control circuit will:
    A. Use holding contacts
    B. Connect holding contacts in series with the start button
    C. Connect holding contacts in parallel with the start button
    D. Not use holding contacts

  12. In regards to the drawing, the best label for the pushbutton labelled “Z” would be:
    A. Stop
    B. Jog
    C. Run
    D. Reset

  13. In regards to the drawing, the best label for pushbutton “Y” would be:
    A. Stop
    B. Jog
    C. Run
    D. Reset
    Use the following image to answer questions 14 and 15.

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  14. What is the minimum number of control circuit conductors required in Conduit A?
    A. 2 wires
    B. 3 wires
    C. 4 wires
    D. 5 wires

  15. What is the minimum number of control circuit conductors required in Conduit B?
    A. 2 wires
    B. 3 wires
    C. 4 wires
    D. 5 wires

  16. Timed relays are the best method to provide plugging for a motor. True or false?

  17. A time-delay relay includes both timed and instantaneous contacts. True or false?

  18. A N.C.T.C contact will be open immediately after the coil is de-energized. True or false?

  19. A N.O.T.O contact will be closed while the coil of the relay is energized. True or false?

  20. A N.C.T.O designation refers to an off-delay timer. True or false?

  21. The electrical interlocks in a reversing magnetic starter are:
    A. Normally closed contacts
    B. Normally open contacts
    C. In parallel with the forward and reverse pushbuttons
    D. Controlled by the timing relays necessary for circuit operation

  22. Overload protection for motors is achieved by connecting:
    A. Thermal sensing elements in series with the motor
    B. A reset relay in series with the motor
    C. Cartridge fuses in series with the motor
    D. A set of N.C contacts in series with the motor

  23. Jogging refers to a:
    A. Motor that is not capable of developing constant torque
    B. Motor that is polyphasing
    C. Motor that periodically starts and stops
    D. Method used to stop a motor for exact positioning
    Answers

  24. B

  25. D

  26. C

  27. B and C

  28. A and C

  29. C

  30. A

  31. D

  32. B

  33. C

  34. D

  35. B

  36. C

  37. ?

  38. C

  39. False

  40. True

  41. False

  42. True

  43. False

  44. A

  45. A

  46. D

Reference

Basic Motor Control by Aaron Lee and Chad Flinn is used under a CC BY 4.0 Licence.