Quiz: Motor Controls

GENERAL QUESTIONS

1. Identify five types of limit switches and explain where each would be used.

2. Use the diagrams in this figure and explain how the drum switch can reverse the direction of rotation for a single-phase motor, a three-phase motor, and a DC motor.

3. Use this diagram to explain how the jog circuit must modify the traditional three-wire control circuit so it won't latch in.

4. Explain the operation of each of the three level-type pilot devices shown here.

5. Use this table to select the correct enclosure for the following applications: dust-tight indoors, rainproof and sleet-resistant outdoors, general-purpose indoors, oil-tight and dust-tight indoors.

6. Explain the two types of interlocks that are used in the forward and reversing circuit shown here that prevent the forward and reverse motor starter coils from being energized at the same time.

7. Explain how motor controls must interface with industrial electronic controls to make modern automated machinery run.

8. A dual-element fuse has a slow-blow section and a short-circuit section. Explain how each section works.

9. Explain what type of problem you would look for if you were troubleshooting this start/stop circuit if the motor starter coil would only remain energized as long as the start push button is depressed.

10. Explain how you would test the level switches shown here if you suspected they were not closing to energize the pump.

TRUE OR FALSE

1. A short-circuit current will occur if an L1 wire comes into contact with an L2 wire.

2. ______ When a slow overcurrent occurs the neck-down section of a dual-element fuse will open.

3. _______ A jogging circuit is used to interlock a motor starter during a sequence move.

4. _______ A three-wire control circuit uses NO auxiliary contacts of the motor starter to seal in the start push button.

5. _______ In this diagram, the level switch will close when the level that is being sensed increases.

6. _______ A drum switch can be used to reverse the direction of a single-phase AC motor, a three-phase AC motor, or a DC motor.

7. _______ The auxiliary contacts found between terminals 2 and 3 on a motor starter are used to seal in the start push button in a three-wire control circuit.

8. _______ NEMA stands for National Electrical Manufacturers Association.

9. _______ When a switch like the one shown here is found to be faulty on a piece of equipment, you must remove the wires from the contact block so they can be connected on the new switch you are installing.

10. _______ When a drum switch is used to reverse the direction of rotation of a single- phase AC motor, both the run windings and the start windings are reversed.

MULTIPLE CHOICE

1. Interruption capacity is _______

a. the ability of a fuse to withstand larger currents and clear them safely.

b. the ability of a fuse to open during a slow overcurrent.

c. the ability of a fuse to detect the difference between short-circuit current and slow over- current.

2. In this diagram, motor starter M1 will always be running before motor starter M2 can become energized because _______

a. M1 coil requires a larger voltage than M2 coil.

b. M1 coil is in series with M2 coil.

c. M1 contacts are in series with M2 coil.

3. When two extra stop push buttons are added to a start/stop circuit, the stop buttons must be wired ______

a. in series with the other stop push button.

b. in parallel with the other stop push button.

c. in parallel with the start push button.

4. In this schematic, which pressure switch will protect the circuit when it's in the auto position?

a. only pressure switch B.

b. only pressure switch A.

c. both pressure switches A and B.

5. When two extra start push buttons are added to a start/stop circuit, the start push buttons must be wired _______

a. in series with the other stop push button.

b. in parallel with the other stop push button.

c. in parallel with the start push button.

6. A provides a sequential diagram of a circuit that is easy to troubleshoot.

a. ladder diagram

b. wiring diagram

c. pictorial diagram

7. A l wire with THWN insulation can safely carry amps.

a. 30

b. 25

c. 20

8. A 10-gauge wire is _______ than a 6 wire.

a. smaller

b. larger

c. can’t tell unless you know the type of insulation on each wire.

9. A type enclosure is water-tight, dust-tight, and corrosion resistant on indoor and outdoor applications.

a. 3

b. 4

c. 4X

10. The NC contacts on a motor starter that are identified as OL are used to _______

a. open the control circuit when the motor draws too much current.

b. open the load circuit when the motor draws too much current.

c. open the control circuit when the motor starter coil draws too much current.

PROBLEMS

1. Draw the symbols for an NO limit switch, an NO held closed limit switch, an NC limit switch, and an NC held open limit switch.

2. Draw the symbols for NO and NC pressure switches that are used for a high-pressure application, and NO and NC pressure switches that are used for a low-pressure application.

3. Draw a two-wire control circuit of a limit switch and a motor as a ladder diagram.

4. Use this table to select a wire that will carry 30 A and has THHN insulation that can withstand 90°C.

5. Draw a two-wire control circuit of a limit switch and a motor as a wiring diagram.

6. Draw a ladder diagram of a three-wire control circuit that has a stop push button, a start push button, and a motor starter.

7. Draw a wiring diagram of a three-wire control circuit that has a stop push button, a start push button, and a motor starter.

8. Draw the diagrams of a drum switch whenit's in the reverse position, the off position, and the forward position.

9. Draw a sketch of a single-element fuse and explain how it clears excess current.

10. Draw a sketch of a dual-element fuse and explain how it clears short-circuit current and how it senses slow overcurrent.