Electric Motor Control
10th Edition
ISBN: 9781133702818
Author: Herman
Publisher: CENGAGE L
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Textbook Question
Chapter 2, Problem 1SQ
If the contacts on a manual starter cannot be closed immediately after a motor overload has tripped them open, what is the probable reason?
Expert Solution & Answer
To determine
Explain the probable reason for allowing the time duration to reset the starter contacts after they tripped off by the overload protection equipment of the motor.
Explanation of Solution
Discussion:
The overload protection of the motor trips off (open) the contacts of a motor starter when the load exceeds the normal range. The overload protection equipment (heater) gets heated during the overload condition.
The contacts of the starter can reset only after the overload protection equipment cools completely. If the contacts are closed immediately, the heater does not cool properly due to the insufficient time and it lead to damage the motor as the overload still exists.
Conclusion:
Thus, the contacts of the motor starter cannot close immediately when the motor overload has tripped them open.
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Chapter 2 Solutions
Electric Motor Control
Ch. 2 - If the contacts on a manual starter cannot be...Ch. 2 - If the handle of an installed motor starter is in...Ch. 2 - How may an automatic operation be achieved when a...Ch. 2 - What does the term trip-free mean as it relates to...Ch. 2 - Prob. 5SQCh. 2 - Prob. 6SQCh. 2 - Prob. 7SQCh. 2 - Prob. 8SQCh. 2 - Select the best answer for each of the following....Ch. 2 - Select the best answer for each of the following....
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- Advance Motor Control 1. Why are contacts often disconnected in series when controlling small motors 2. Why are clapper type contactors generally used to control DC device 3. What is the purpose of FCR (field current relay)arrow_forwardThe starter must never operate for more than sixty seconds at a time and should rest for two minutes between extended cranking ? True or falsearrow_forwardAt standstill condition, the back emf is zero, so the motor can be safely turned ON without a starter. Select one: OTrue O Falsearrow_forward
- Select the best answer for each of the following. When the reset button does not reestablish the control circuit after an overload, the probable cause is a. the overload heater is too small. b. the overload trip has not cooled sufficiently. c. the auxiliary contacts are defective. d. the overload heater is burned out.arrow_forwardWhat is the principal difference between a contactor and a motor starter?arrow_forwardA starter turns very slowly and has excessive cranking current draw. When removed from the vehicle and bench tested, the starter spins normally and current draw is within specifications. Technician A says poor battery connections may be the cause. Technician B says an internal engine problem may be the cause. Who is correct?arrow_forward
- Make a conventional wiring diagram to rotate a 3phase motor cw ccw with indicator lamps. When the motor rotates, a single acting cylinder extends? What happens if push buttons for cw and ccw are pressed at the same time?arrow_forwardSelect the best answer for each of the following. If an operator pushes a start button on a three-phase induction motor and the motor starts to hum, but not run, the probable trouble is a. one fuse is blown and the motor is single phasing. b. the overload trip needs resetting. c. the auxiliary contact is shorted. d. one phase is grounded.arrow_forwardHow may an automatic operation be achieved when a manual motor starter is used?arrow_forward
- One reason for the use of a reduced voltage starter would be to reduce the high starting current drawn by the motor. True or false?arrow_forward2. In the motor control circuit of Figure 11 in your study unit, the operation of any one of the overload relays has which of the following effects?A. The motor only runs two phases.B. The motor operates normally. C. The auxiliary contact M closes. D. The motor stopsarrow_forwardTechnician A says when testing the voltage output, if the charging voltage is too high, the cause could be an open field wire from the regulator. Technician B says a loose or glazed drive belt could be the cause of too high charging voltage. Who is correct? A only B only Both A and B Neither A or B Technician A says that poor connection at the generator output wire can cause charging systems problems. Technician B says that many charging system circuits contain a circuit protection device. Who is correct? A only B only Both A and B Neither A or Barrow_forward
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