Week 8 quiz "Electricity" Units 33 & 34 & class lecture
12. Although a capacitor-start induction-run motor has a high starting torque, the motor should not be started more than two times per hour. True False
False
5. The speed of the shaded pole induction motor is determined by the same factors that determine the synchronous speed of other induction motors: frequency and speed of stator poles. True False
False
7. The rotor of a squirrel-cage motor is easy to test in the field. True False
False
14. A periodic maintenance schedule can include a lubrication schedule to ensure proper lubrication. True False
True
17. When determining the overload size for a motor, the nameplate current rating of the motor is used instead of the current values listed in the NEC motor tables (T430.247-T430.250). True False
True
4. In a split-phase motor, synchronous speed is determined by the same two factors that determined the synchronous speed for a three-phase motor: number of stator poles per phase and frequency of the applied voltage. True False
True
8. If periodic preventive maintenance on electric motors is not desired or feasible, vibration sensors on the motor shaft can warn of impending bearing failure before it occurs. True False
True
9. To test an armature for an open winding, connect the leads of an ohmmeter to two adjacent commutator bars. True False
True
15. In direct current machines, the segments between commutator bars can become shorted due to a buildup of ____ caused by the wearing of the brushes. a. carbon b. iron c. copper d. steel
a. carbon
18. According to NEC 110.14(C), a conductor is to be selected and coordinated as to not exceed the ____ temperature rating of any connected termination, any connected conductor, or any connected device. a. lowest b. average c. highest d. stated
a. lowest
16. The stator of a split-phase motor contains two separate windings, the start winding and the ____ winding. a. run b. end c. fixed d. Ammortiseur
a. run
3. Rotating a rotor ____ by hand may help to reveal a bad bearing. a. shaft b. brush c. commutator bar d. grease fitting
a. shaft
20. NEC 430.22 states that conductors supplying a single motor shall have an ampacity of not less than ____% of the motor full load current. a. 150 b. 125 c. 200 d. 110
b. 125
10. Although it is permissible to use non-time-delay fuses and instantaneous-trip circuit breakers, most motor circuits are protected by dual-element time-delay fuses or ____-time circuit breakers. a. converse b. half c. inverse d. reverse
c. inverse
2. The direction of rotation for a split-phase motor is determined by the direction of rotation of the magnetic field created by the run and start windings when the motor ____. a. is idling b. has been running for at least five minutes c. is first started d. is turned off
c. is first started
11. Many split phase motors are designed for operation on _____. a. 120 Hz systems b. 277/480 volts c. Delta-Wye center-tapped systems d. 120 or 240 volts Correct
d. 120 or 240 volts
19. If for some reason a fuse will not permit a motor to start without blowing, NEC 430.52(C)(1) Exception 2 (2) states that the rating of a dual-element time-delay fuse may be increased to a maximum of ____% of the full load motor current. a. 125 b. 200 c. 175 d. 225
d. 225
1. Motors that are not hermetically sealed use a ____ switch to disconnect the start windings from the circuit. a. magnetic b. rotation c. hermetic d. centrifugal
d. centrifugal
6. A device that can be used to test an armature is called a ____. a. husker b. Laminator c. coiler d. growler
d. growler
13. In a Split-phase motor, the speed of the rotating magnetic field is called __________ speed. a. Excitation b. Full-load c. maximum d. synchronous
d. synchronous