Understanding Motor Controls
4th Edition
ISBN: 9781337798686
Author: Stephen L. Herman
Publisher: Delmar Cengage Learning
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Chapter 37, Problem 11RQ
To determine
The size of the circuit breaker used.
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Chapter 37 Solutions
Understanding Motor Controls
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- If dual-element time delay fuses are to be used as the short circuit protective device, what size fuses should be used to protect the circuit in question #12? Five 5 HP, three-phase motors with NEMA code B are connected to a 240-volt line. The conductors are copper with type THWN insulation. What size conductor should be used to supply all of these motors?arrow_forwardThe short-circuit protective device supplying the motors in question #10 is an inverse-time circuit breaker. What size circuit breaker should be used?arrow_forwardRefer to the transformer shown in Figure 5-13 to answer the following questions. What is the turns ratio of the winding between points B and E as compared to the winding between points D and E? Figure 5-13 Autotransformer practice problems.arrow_forward
- What is the function of the compensating winding?arrow_forwardA large motor has a full load current rating of 425 amperes. Current transformers with a ratio of 600:5 are used to reduce the current to the overload heaters. What should be the full load current rating of the overload heaters?arrow_forwardRefer to the transformer shown in Figure 5-13 to answer the following questions. The transformer shown in Figure 5-13 is supplying 325 volt amperes to a load. The primary voltage is 240 volts. What is the primary current? Figure 5-13 Autotransformer practice problems.arrow_forward
- Refer to the schematic diagram in Figure 318. Assume that the motor is not running. When the third speed push button is pressed, the motor starts in its lowest speed. After a delay of 3 seconds, the motor accelerates to second speed and 3 seconds later to third speed. After a period of about 1 minute, the fourth speed push button is pressed, but the motor does not accelerate to fourth speed. Which of the following could cause this problem? a. Control relay CR2 coil is open. b. S2 contactor coil is open. c. CR3 coil is shorted. d. S3 contactor coil is open.arrow_forwardName three factors that determine the amount of induced voltage.arrow_forwardAn AC power source is connected across 325 turns of an autotransformer, and the load is connected across 260 turns. What is the turns ratio of this transformer?arrow_forward
- State the physical differences between a run and a start capacitor.arrow_forwardA 10 kVA transformer has a primary voltage rating of 240 volts and a secondary voltage rating of 480 volts. The transformer is connected to a circuit protected by a 100 ampere circuit breaker. The secondary is protected by a 25-ampere fuse. Does the primary require separate overcurrent protection?arrow_forwardA 480-volt three-phase load is rated at 34.5 kVA. It is to be supplied with variable three-phase voltage. Because the load is continuous, the transformers ratings are to be increased by 1.25% of the rated load. Three variable autotransformers are used to supply this load. Refer to Table 4-2 and determine the standard size of each transformer that should be used to make this connection.arrow_forward
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