NEC Requirements for Short-Circuit and Ground-Fault Protection in Branch Circuit...
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Questions and Answers

What is the purpose of using the motor nameplate full-load current to select overload protection?

  • To determine the duty of the motor
  • To select the feeder and branch-circuit wiring
  • To protect the motor from overload (correct)
  • To prevent dangerous overheating

    • What is the maximum percentage of motor full-load current at which a thermal or electronically protected motor can trip?

  • 115%
  • 140% (correct)
  • 170%
  • 156%

    • What is the difference between a 'continuous-duty motor' and a 'continuous load'?

  • A continuous-duty motor refers to a motor that operates continuously, while a continuous load can carry a 25% overload for an extended period without damage.
  • A continuous-duty motor can carry a 50% overload for an extended period without damage, while a continuous load refers to a load that operates continuously.
  • There is no difference between a continuous-duty motor and a continuous load.
  • A continuous-duty motor can carry a 25% overload for an extended period without damage, while a continuous load refers to a load that operates continuously. (correct)

    • What is the purpose of a thermal protector in a motor?

    <p>To prevent dangerous overheating of the motor due to overload and failure to start</p> Signup and view all the answers

    According to the information provided, what is the ampacity of the conductors between the controller and the motor?

    <p>125 percent of the motor full-load current rating</p> Signup and view all the answers

    What is the running current of the motor in relation to the motor full-load current?

    <p>50 percent</p> Signup and view all the answers

    Which of the following is NOT a classification of service in Table 430.22(E)?

    <p>Varying duty</p> Signup and view all the answers

    When are branch-circuit conductors for a 5-minute short-time duty rated motor permitted to be sized smaller than for a 60-minute rated motor?

    <p>When the motor is running for 5 minutes and then off for 55 minutes</p> Signup and view all the answers

    According to the text, which of the following is true about the tap conductors?

    <p>They must be 6 AWG copper or 4 AWG aluminum or larger</p> Signup and view all the answers

    According to the text, how should the tap conductors be sized for a single motor load?

    <p>At least 125 percent of the full-load current value for the motor</p> Signup and view all the answers

    According to the text, what is the principle behind sizing conductors for short-circuit and ground-fault protection of branch circuits or feeders?

    <p>The conductors should have an ampacity equal to 125 percent of the full-load current of the largest motor</p> Signup and view all the answers

    According to the text, how are the reduced-size tap conductors protected from overload?

    <p>By the fuses or circuit breaker where the tap conductors terminate</p> Signup and view all the answers

    According to the text, what additional requirements must a tap conductor installation meet?

    <p>10 feet, 25 feet, or 100 feet distance limits</p> Signup and view all the answers

    According to the text, what does 430.53 specify for branch-circuit conductors to multi-motor equipment?

    <p>The maximum rating of the branch-circuit short-circuit and ground-fault protective device</p> Signup and view all the answers

    According to the text, how should the ampacity of conductors supplying multimotor and combination-load equipment be determined?

    <p>The minimum circuit ampacity marked on the equipment</p> Signup and view all the answers

    According to the text, what is the minimum allowable conductor size for a combination lighting and motor load?

    <p>The minimum conductor ampacity determined by adding the lighting load and the motor load</p> Signup and view all the answers

    According to 430.23(A) of the text, what is the ampacity requirement for conductors connecting the secondary of a wound-rotor AC motor to its controller for continuous duty?

    <p>125 percent of the full-load secondary current of the motor</p> Signup and view all the answers

    According to 430.24 of the text, what is the ampacity requirement for conductors supplying several motors or a motor(s) and other load(s)?

    <p>The sum of 125 percent of the full-load current rating of the highest rated motor, the sum of the full-load current ratings of all the other motors in the group, 100 percent of the noncontinuous non-motor load, and 125 percent of the continuous non-motor load</p> Signup and view all the answers

    According to the text, what is the ampacity requirement for conductors between the controller and resistor when the secondary resistor is separate from the controller?

    <p>As shown in Table 430.23(C)</p> Signup and view all the answers

    According to the text, what is the ampacity requirement for conductors connecting the secondary of a wound-rotor AC motor to its controller for other than continuous duty?

    <p>Not less than that specified in Table 430.22(E)</p> Signup and view all the answers

    Which of the following is the reduced starting voltage of a polyphase induction motor in a wye-start configuration, as mentioned in the text?

    <p>0.5774</p> Signup and view all the answers

    What is the starting current of a polyphase induction motor in a wye-start configuration, as mentioned in the text?

    <p>58 percent</p> Signup and view all the answers

    What is the ampacity requirement for conductors between the controller and the motor in a delta-connected motor load, as mentioned in the text?

    <p>72 percent of the motor full-load current rating</p> Signup and view all the answers

    Which one of the following is a method for protecting a motor of 1 hp or less against overload, as mentioned in the text?

    <p>Using a separate overload device</p> Signup and view all the answers

    Which one of the following is NOT a requirement for a thermal protector or an electronically protected motor, as mentioned in the text?

    <p>Preventing dangerous overheating due to failure of the motor</p> Signup and view all the answers

    Under what conditions is a protective device integral with a motor permitted to protect the motor against damage due to failure to start, as mentioned in the text?

    <p>If the assembly is also equipped with other safety controls that protect the motor against damage due to failure to start</p> Signup and view all the answers

    According to the text, what is the maximum rating for a time-delay (dual-element) fuse in relation to the full-load current?

    <p>225 percent</p> Signup and view all the answers

    According to the text, what is the maximum rating for an inverse time circuit breaker for full-load currents greater than 100 amperes?

    <p>300 percent</p> Signup and view all the answers

    According to the text, what is the maximum rating for a fuse of 601–6000 ampere classification in relation to the full-load current?

    <p>300 percent</p> Signup and view all the answers

    According to the text, what is the maximum percentage of the motor full-load current at which a thermal or electronically protected motor can trip?

    <p>1700 percent</p> Signup and view all the answers

    What is the purpose of using a higher class overload relay in a motor?

    <p>To provide a longer motor acceleration time</p> Signup and view all the answers

    What is the maximum trip current of the overload device for motors with a marked temperature rise of 40°C or less?

    <p>140% of motor nameplate full-load current rating</p> Signup and view all the answers

    Which type of motor is permitted to have overload protection furnished by the branch-circuit short-circuit and ground-fault protective device if it is within sight from the controller?

    <p>Motors with a horsepower of one or less</p> Signup and view all the answers

    What is the ampacity requirement for conductors between the controller and the motor in a delta-connected motor load?

    <p>Not specified in the text</p> Signup and view all the answers

    Which of the following is NOT a type of fault that can cause the protective device to open the circuit?

    <p>Arc fault</p> Signup and view all the answers

    What is the purpose of a motor overload device?

    <p>To protect the motor against overcurrent</p> Signup and view all the answers

    Which of the following is NOT a requirement for a motor overload device that can automatically restart a motor after overload tripping?

    <p>It must have a time delay</p> Signup and view all the answers

    What is the purpose of a motor overload sensing device connected to a supervised alarm?

    <p>To initiate corrective action or an orderly shutdown</p> Signup and view all the answers

    According to Table 430.52(C)(1), what is the maximum rating or setting of the branch-circuit short-circuit and ground-fault protective device for a squirrel cage motor other than Design B energy-efficient or Design B premium efficiency?

    <p>300</p> Signup and view all the answers

    According to the information provided, what is the maximum rating or setting of the branch-circuit short-circuit and ground-fault protective device for a synchronous motor?

    <p>250</p> Signup and view all the answers

    According to the text, what is the maximum rating or setting of the branch-circuit short-circuit and ground-fault protective device for a DC (constant voltage) motor?

    <p>150</p> Signup and view all the answers

    According to the text, what is the maximum rating or setting of the branch-circuit short-circuit and ground-fault protective device for a wound-rotor motor?

    <p>150</p> Signup and view all the answers

    According to the text, what is the ampacity requirement for conductors supplying power electronic devices in a solid-state motor controller system?

    <p>The ampacity is determined based on the marking for replacement fuses provided adjacent to the fuses.</p> Signup and view all the answers

    According to the text, what is the ampacity requirement for conductors supplying each winding in a motor?

    <p>The ampacity is determined based on the full-load current of the highest full-load current winding.</p> Signup and view all the answers

    According to the text, what is the horsepower rating requirement for the motor controller of each winding in a motor?

    <p>The horsepower rating is determined based on the horsepower rating of the winding with the highest horsepower rating.</p> Signup and view all the answers

    Which of the following is true about motor overload protection during the starting period on an automatically started motor, according to the text?

    <p>The motor overload protection must be shunted or cut out during the starting period.</p> Signup and view all the answers

    Where should a fuse be inserted for motor overload protection in a 3-wire, 3-phase ac supply system with one conductor grounded, as mentioned in the text?

    <p>In each ungrounded conductor and the grounded conductor.</p> Signup and view all the answers

    How many overload units are required for motor overload protection in a 2-phase ac, 4-wire system, as specified in Table 430.37 of the text?

    <p>Two, one for each phase in ungrounded conductors.</p> Signup and view all the answers

    When can a motor controller serve as an overload device, according to the text?

    <p>If the number of overload units complies with Table 430.37 and if these units are operative in both the starting and running position.</p> Signup and view all the answers

    Which of the following is true about a self-protected combination motor controller?

    <p>It combines the functions of overload protection, short-circuit protection, and disconnect into a single unit.</p> Signup and view all the answers

    When is a motor short-circuit protector permitted to protect a motor against damage due to failure to start?

    <p>If it is part of a listed combination motor controller with coordinated motor overload protection and short-circuit and ground-fault protection.</p> Signup and view all the answers

    What is the maximum rating for an inverse time circuit breaker for full-load currents greater than 100 amperes?

    <p>Not specified in the text</p> Signup and view all the answers

    According to the text, what is the maximum rating or setting of the branch-circuit short-circuit and ground-fault protective device for a squirrel cage motor other than Design B energy-efficient or Design B premium efficiency?

    <p>Not over 20 amperes</p> Signup and view all the answers

    According to the text, what is the maximum rating or setting of the branch-circuit short-circuit and ground-fault protective device for a wound-rotor motor?

    <p>Not over 15 amperes</p> Signup and view all the answers

    According to the text, what is the maximum rating or setting of the branch-circuit short-circuit and ground-fault protective device for a DC (constant voltage) motor?

    <p>Not over 6 amperes</p> Signup and view all the answers

    According to the text, what is the maximum rating or setting of the branch-circuit short-circuit and ground-fault protective device for a synchronous motor?

    <p>Not over 1 horsepower</p> Signup and view all the answers

    According to the text, what is the purpose of using dual-element (time-delay) fuses for motor overload protection?

    <p>To provide better protection by using smaller fuses with lower ratings</p> Signup and view all the answers

    According to the text, what is the maximum rating or setting of the branch-circuit short-circuit and ground-fault protective device for a DC (constant voltage) motor?

    <p>The maximum rating or setting is determined by Table 430.52(C)(1)</p> Signup and view all the answers

    According to the text, what is the ampacity requirement for conductors between the controller and resistor when the secondary resistor is separate from the controller?

    <p>The ampacity requirement is determined by the resistor current rating</p> Signup and view all the answers

    According to the text, what is the maximum rating for a time-delay (dual-element) fuse in relation to the full-load current?

    <p>The maximum rating is determined by Table 430.52(C)(1)</p> Signup and view all the answers

    According to the text, what is the maximum rating or setting of the branch-circuit short-circuit and ground-fault protective device for a squirrel cage motor other than Design B energy-efficient or Design B premium efficiency?

    <p>250% of the motor full-load current</p> Signup and view all the answers

    According to the text, what is the maximum rating for a time-delay (dual-element) fuse in relation to the full-load current?

    <p>200% of the full-load current</p> Signup and view all the answers

    According to the text, what is the maximum rating or setting of the branch-circuit short-circuit and ground-fault protective device for a wound-rotor motor?

    <p>125% of the motor full-load current</p> Signup and view all the answers

    According to the text, what is the maximum length of tap conductors supplying a motor that is part of a group installation?

    <p>25 feet</p> Signup and view all the answers

    According to the text, what is the minimum ampacity requirement for tap conductors from the point of the tap to the controller?

    <p>One-tenth the rating or setting of the branch-circuit short-circuit and ground-fault protective device</p> Signup and view all the answers

    According to the text, what is the maximum ampacity requirement for tap conductors supplying a motor that is part of a group installation?

    <p>One-third the ampacity of the main branch-circuit conductors</p> Signup and view all the answers

    According to the text, what is the maximum ampacity requirement for tap conductors from the point of the tap to the controller?

    <p>One-tenth the rating or setting of the branch-circuit short-circuit and ground-fault protective device</p> Signup and view all the answers

    Which of the following is NOT a requirement for a motor overload device that can automatically restart a motor after overload tripping?

    <p>The device must have a current rating equal to or greater than the motor full-load current</p> Signup and view all the answers

    According to the text, what is the maximum rating or setting of the branch-circuit short-circuit and ground-fault protective device for a squirrel cage motor other than Design B energy-efficient or Design B premium efficiency?

    <p>150% of the motor full-load current</p> Signup and view all the answers

    According to the text, what is the ampacity requirement for conductors supplying power electronic devices in a solid-state motor controller system?

    <p>125% of the motor full-load current</p> Signup and view all the answers

    According to the text, what is the maximum rating or setting of the branch-circuit short-circuit and ground-fault protective device for a wound-rotor motor?

    <p>80% of the motor full-load current</p> Signup and view all the answers

    Which of the following is a requirement for tap conductors between the branch circuit and listed manual motor controllers?

    <p>The length of the motor tap conductors does not exceed 5 m (16 ft) and the tap conductors comply with all of the following: The ampacity of the tap conductors is not less than one-third of the rating or setting of the branch-circuit short-circuit ground-fault protective device. The conductors from the motor controller to the motor shall have an ampacity in accordance with 430.22. The conductors from the point of the tap to the motor controller(s) shall be suitably protected from physical damage and enclosed either by an enclosed motor controller or by a raceway.</p> Signup and view all the answers

    Which of the following is a condition that must be met for conductors to the motor to have an ampacity less than the ampacity of the branch-circuit conductors?

    <p>The conductor ampacity must be less than one-third the ampacity of the branch-circuit conductors.</p> Signup and view all the answers

    Which of the following is a requirement for tap conductors between the branch circuit and a listed manual motor controller marked 'Suitable for Tap Conductor Protection in Group Installations'?

    <p>The length of the motor tap conductors does not exceed 5 m (16 ft) and the tap conductors comply with all of the following: The ampacity of the tap conductors is not less than one-third of the rating or setting of the branch-circuit short-circuit ground-fault protective device. The conductors from the motor controller to the motor shall have an ampacity in accordance with 430.22. The conductors from the point of the tap to the motor controller(s) shall be suitably protected from physical damage and enclosed either by an enclosed motor controller or by a raceway.</p> Signup and view all the answers

    According to Table 430.72(B)(2), what is the maximum rating of the protective device(s) for conductors within the motor control equipment enclosure?

    <p>100 amperes</p> Signup and view all the answers

    According to Table 430.72(B)(2), what is the maximum rating of the protective device(s) for conductors that extend beyond the motor control equipment enclosure?

    <p>45 amperes</p> Signup and view all the answers

    According to the text, what is the maximum rating or setting of the branch-circuit short-circuit and ground-fault protective device for a wound-rotor motor?

    <p>140 amperes</p> Signup and view all the answers

    Which of the following is a requirement for motor control centers according to 110.21?

    <p>Marking shall include common power bus current rating and motor control center short-circuit current rating</p> Signup and view all the answers

    What should motor control units in a motor control center comply with?

    <p>430.8</p> Signup and view all the answers

    What information should be documented and made available for those authorized to inspect, install, or maintain the installation?

    <p>Available fault current at the motor control center and the date of installation</p> Signup and view all the answers

    According to the text, what is the maximum rating for a time-delay (dual-element) fuse in relation to the full-load current?

    <p>200 percent</p> Signup and view all the answers

    According to the text, what is the maximum rating or setting of the branch-circuit short-circuit and ground-fault protective device for a squirrel cage motor other than Design B energy-efficient or Design B premium efficiency?

    <p>400 percent</p> Signup and view all the answers

    According to the text, what is the maximum rating or setting of the branch-circuit short-circuit and ground-fault protective device for a wound-rotor motor?

    <p>400 percent</p> Signup and view all the answers

    According to the text, what is the maximum ampacity requirement for tap conductors from the point of the tap to the controller?

    <p>50 percent</p> Signup and view all the answers

    Which of the following is NOT a requirement for motor control centers to be used as service equipment?

    <p>Having a second service disconnecting means</p> Signup and view all the answers

    What is the maximum rating or setting of the branch-circuit short-circuit and ground-fault protective device for a squirrel cage motor other than Design B energy-efficient or Design B premium efficiency?

    <p>300% of full-load current</p> Signup and view all the answers

    What is the minimum wire-bending space at the motor control center terminals and minimum gutter space, according to the text?

    <p>312.6</p> Signup and view all the answers

    What is the maximum trip current of the overload device for motors with a marked temperature rise of 40°C or less?

    <p>135% of full-load current</p> Signup and view all the answers

    According to the text, what is the purpose of using double-pole control devices with one pole in each of the two control lines in motor and motor control circuits?

    <p>To prevent inadvertent motor starting</p> Signup and view all the answers

    According to the text, where should the disconnecting means for motor control circuits be located when separate devices are used?

    <p>Immediately adjacent to each other</p> Signup and view all the answers

    According to the text, under what conditions are motor control circuit disconnecting means permitted to be remote from the motor controller power supply disconnecting means?

    <p>When the opening of one or more motor control circuit disconnecting means can result in potentially unsafe conditions</p> Signup and view all the answers

    According to the text, what is the requirement for a transformer or other device used to obtain a reduced voltage for the motor control circuit when it is located in the motor controller enclosure?

    <p>It shall be connected to the load side of the disconnecting means</p> Signup and view all the answers

    Which of the following is a requirement for a motor controller to be placed in a permanently grounded conductor, as mentioned in the text?

    <p>The motor controller must be designed so that the grounded conductor cannot be opened without simultaneously opening all conductors of the circuit.</p> Signup and view all the answers

    Which of the following is an exception to the requirement of providing each motor with an individual motor controller, as stated in the text?

    <p>When a group of motors is located in a single room within sight from the motor controller location.</p> Signup and view all the answers

    Which of the following is a type of motor that requires speed-limiting devices or other speed-limiting means, as mentioned in the text?

    <p>All of the above</p> Signup and view all the answers

    What is the purpose of using speed-limiting devices or means in motors, as stated in the text?

    <p>To prevent the motor from starting under a weakened field.</p> Signup and view all the answers

    Which one of the following is a requirement for a motor controller to be used for all motors, as mentioned in the text?

    <p>The motor controller must have a horsepower rating equal to or higher than the motor's horsepower rating.</p> Signup and view all the answers

    Which one of the following is true about molded case switches used as motor controllers, as mentioned in the text?

    <p>Molded case switches are permitted as motor disconnecting means.</p> Signup and view all the answers

    Which one of the following is a requirement for a motor controller to be used for stationary motors of 2 horsepower or less and 300 volts or less, as mentioned in the text?

    <p>The motor controller must have an ampere rating not less than twice the full-load current rating of the motor.</p> Signup and view all the answers

    Which one of the following is true about motor controllers with a straight voltage rating and a slash rating, as mentioned in the text?

    <p>Motor controllers with a slash rating can be applied in circuits with any nominal voltage between conductors.</p> Signup and view all the answers

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