280 Copyright Goodheart-Willcox Co., Inc. ____________ 12. Th e current magnetic relay has _____. A. a high resistance coil and NC contacts B. a low resistance coil and NC contacts C. a high resistance coil and NO contacts D. a low resistance coil and NO contacts ____________ 13. Th e potential relay has _____. A. a high resistance coil and NC contacts B. a low resistance coil and NC contacts C. a high resistance coil and NO contacts D. a low resistance coil and NO contacts ____________ 14. Which is not a split-phase motor? A. PSC. B. RSIR. C. CSR. D. Th ree-phase. ____________ 15. What is not true about three-phase motors? A. It has three run windings. B. Its rotation cannot be changed. C. It has higher torque than single-phase motors. D. It can be used in hermetic compressors. ____________ 16. True or False? Single phasing a three-phase motor means that the motor is operating on only two hot legs. ____________ 17. What is not true about an ECM motor? A. It uses a permanent magnet rotor. B. Th e stator has three run windings. C. It generates three-phase power from single-phase power. D. It is used in applications with greater than 5 hp. ____________ 18. Th e stator windings generate a magnetic fi eld that induces a current in the rotor. Th e rotor current is _____. A. in phase with the stator current B. 90° out of phase with stator current C. 180° out of phase with the stator current D. 360° out of phase with the stator current ____________ 19. True or False? Centrifugal switches can be used inside hermetic compressors to remove the start winding. ____________ 20. True or False? Circuit breakers are used to protect motors from overheating. Critical Thinking 1. A potential relay coil fails (breaks) while a CSR motor is running. What happens? ______________________________________________________________________________________________________________ ______________________________________________________________________________________________________________ ______________________________________________________________________________________________________________ 2. When measuring resistance of a hermetic compressor motor, the resistance between the run terminal and the common terminal is the same as the resistance between the start terminal and the common terminal. What is wrong? ______________________________________________________________________________________________________________ ______________________________________________________________________________________________________________ ______________________________________________________________________________________________________________