100 Questions
What is the purpose of using the motor nameplate full-load current to select overload protection?
To protect the motor from overload
What is the maximum percentage of motor full-load current at which a thermal or electronically protected motor can trip?
140%
What is the 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.
What is the purpose of a thermal protector in a motor?
To prevent dangerous overheating of the motor due to overload and failure to start
According to the information provided, what is the ampacity of the conductors between the controller and the motor?
125 percent of the motor full-load current rating
What is the running current of the motor in relation to the motor full-load current?
50 percent
Which of the following is NOT a classification of service in Table 430.22(E)?
Varying duty
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?
When the motor is running for 5 minutes and then off for 55 minutes
According to the text, which of the following is true about the tap conductors?
They must be 6 AWG copper or 4 AWG aluminum or larger
According to the text, how should the tap conductors be sized for a single motor load?
At least 125 percent of the full-load current value for the motor
According to the text, what is the principle behind sizing conductors for short-circuit and ground-fault protection of branch circuits or feeders?
The conductors should have an ampacity equal to 125 percent of the full-load current of the largest motor
According to the text, how are the reduced-size tap conductors protected from overload?
By the fuses or circuit breaker where the tap conductors terminate
According to the text, what additional requirements must a tap conductor installation meet?
10 feet, 25 feet, or 100 feet distance limits
According to the text, what does 430.53 specify for branch-circuit conductors to multi-motor equipment?
The maximum rating of the branch-circuit short-circuit and ground-fault protective device
According to the text, how should the ampacity of conductors supplying multimotor and combination-load equipment be determined?
The minimum circuit ampacity marked on the equipment
According to the text, what is the minimum allowable conductor size for a combination lighting and motor load?
The minimum conductor ampacity determined by adding the lighting load and the motor load
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?
125 percent of the full-load secondary current of the motor
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)?
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
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?
As shown in Table 430.23(C)
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?
Not less than that specified in Table 430.22(E)
Which of the following is the reduced starting voltage of a polyphase induction motor in a wye-start configuration, as mentioned in the text?
0.5774
What is the starting current of a polyphase induction motor in a wye-start configuration, as mentioned in the text?
58 percent
What is the ampacity requirement for conductors between the controller and the motor in a delta-connected motor load, as mentioned in the text?
72 percent of the motor full-load current rating
Which one of the following is a method for protecting a motor of 1 hp or less against overload, as mentioned in the text?
Using a separate overload device
Which one of the following is NOT a requirement for a thermal protector or an electronically protected motor, as mentioned in the text?
Preventing dangerous overheating due to failure of the motor
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?
If the assembly is also equipped with other safety controls that protect the motor against damage due to failure to start
According to the text, what is the maximum rating for a time-delay (dual-element) fuse in relation to the full-load current?
225 percent
According to the text, what is the maximum rating for an inverse time circuit breaker for full-load currents greater than 100 amperes?
300 percent
According to the text, what is the maximum rating for a fuse of 601–6000 ampere classification in relation to the full-load current?
300 percent
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?
1700 percent
What is the purpose of using a higher class overload relay in a motor?
To provide a longer motor acceleration time
What is the maximum trip current of the overload device for motors with a marked temperature rise of 40°C or less?
140% of motor nameplate full-load current rating
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?
Motors with a horsepower of one or less
What is the ampacity requirement for conductors between the controller and the motor in a delta-connected motor load?
Not specified in the text
Which of the following is NOT a type of fault that can cause the protective device to open the circuit?
Arc fault
What is the purpose of a motor overload device?
To protect the motor against overcurrent
Which of the following is NOT a requirement for a motor overload device that can automatically restart a motor after overload tripping?
It must have a time delay
What is the purpose of a motor overload sensing device connected to a supervised alarm?
To initiate corrective action or an orderly shutdown
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?
300
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?
250
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?
150
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?
150
According to the text, what is the ampacity requirement for conductors supplying power electronic devices in a solid-state motor controller system?
The ampacity is determined based on the marking for replacement fuses provided adjacent to the fuses.
According to the text, what is the ampacity requirement for conductors supplying each winding in a motor?
The ampacity is determined based on the full-load current of the highest full-load current winding.
According to the text, what is the horsepower rating requirement for the motor controller of each winding in a motor?
The horsepower rating is determined based on the horsepower rating of the winding with the highest horsepower rating.
Which of the following is true about motor overload protection during the starting period on an automatically started motor, according to the text?
The motor overload protection must be shunted or cut out during the starting period.
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?
In each ungrounded conductor and the grounded conductor.
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?
Two, one for each phase in ungrounded conductors.
When can a motor controller serve as an overload device, according to the text?
If the number of overload units complies with Table 430.37 and if these units are operative in both the starting and running position.
Which of the following is true about a self-protected combination motor controller?
It combines the functions of overload protection, short-circuit protection, and disconnect into a single unit.
When is a motor short-circuit protector permitted to protect a motor against damage due to failure to start?
If it is part of a listed combination motor controller with coordinated motor overload protection and short-circuit and ground-fault protection.
What is the maximum rating for an inverse time circuit breaker for full-load currents greater than 100 amperes?
Not specified in the text
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?
Not over 20 amperes
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?
Not over 15 amperes
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?
Not over 6 amperes
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?
Not over 1 horsepower
According to the text, what is the purpose of using dual-element (time-delay) fuses for motor overload protection?
To provide better protection by using smaller fuses with lower ratings
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?
The maximum rating or setting is determined by Table 430.52(C)(1)
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?
The ampacity requirement is determined by the resistor current rating
According to the text, what is the maximum rating for a time-delay (dual-element) fuse in relation to the full-load current?
The maximum rating is determined by Table 430.52(C)(1)
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?
250% of the motor full-load current
According to the text, what is the maximum rating for a time-delay (dual-element) fuse in relation to the full-load current?
200% of the full-load current
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?
125% of the motor full-load current
According to the text, what is the maximum length of tap conductors supplying a motor that is part of a group installation?
25 feet
According to the text, what is the minimum ampacity requirement for tap conductors from the point of the tap to the controller?
One-tenth the rating or setting of the branch-circuit short-circuit and ground-fault protective device
According to the text, what is the maximum ampacity requirement for tap conductors supplying a motor that is part of a group installation?
One-third the ampacity of the main branch-circuit conductors
According to the text, what is the maximum ampacity requirement for tap conductors from the point of the tap to the controller?
One-tenth the rating or setting of the branch-circuit short-circuit and ground-fault protective device
Which of the following is NOT a requirement for a motor overload device that can automatically restart a motor after overload tripping?
The device must have a current rating equal to or greater than the motor full-load current
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?
150% of the motor full-load current
According to the text, what is the ampacity requirement for conductors supplying power electronic devices in a solid-state motor controller system?
125% of the motor full-load current
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?
80% of the motor full-load current
Which of the following is a requirement for tap conductors between the branch circuit and listed manual motor controllers?
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.
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?
The conductor ampacity must be less than one-third the ampacity of the branch-circuit conductors.
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'?
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.
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?
100 amperes
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?
45 amperes
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?
140 amperes
Which of the following is a requirement for motor control centers according to 110.21?
Marking shall include common power bus current rating and motor control center short-circuit current rating
What should motor control units in a motor control center comply with?
430.8
What information should be documented and made available for those authorized to inspect, install, or maintain the installation?
Available fault current at the motor control center and the date of installation
According to the text, what is the maximum rating for a time-delay (dual-element) fuse in relation to the full-load current?
200 percent
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?
400 percent
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?
400 percent
According to the text, what is the maximum ampacity requirement for tap conductors from the point of the tap to the controller?
50 percent
Which of the following is NOT a requirement for motor control centers to be used as service equipment?
Having a second service disconnecting means
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?
300% of full-load current
What is the minimum wire-bending space at the motor control center terminals and minimum gutter space, according to the text?
312.6
What is the maximum trip current of the overload device for motors with a marked temperature rise of 40°C or less?
135% of full-load current
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?
To prevent inadvertent motor starting
According to the text, where should the disconnecting means for motor control circuits be located when separate devices are used?
Immediately adjacent to each other
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?
When the opening of one or more motor control circuit disconnecting means can result in potentially unsafe conditions
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?
It shall be connected to the load side of the disconnecting means
Which of the following is a requirement for a motor controller to be placed in a permanently grounded conductor, as mentioned in the text?
The motor controller must be designed so that the grounded conductor cannot be opened without simultaneously opening all conductors of the circuit.
Which of the following is an exception to the requirement of providing each motor with an individual motor controller, as stated in the text?
When a group of motors is located in a single room within sight from the motor controller location.
Which of the following is a type of motor that requires speed-limiting devices or other speed-limiting means, as mentioned in the text?
All of the above
What is the purpose of using speed-limiting devices or means in motors, as stated in the text?
To prevent the motor from starting under a weakened field.
Which one of the following is a requirement for a motor controller to be used for all motors, as mentioned in the text?
The motor controller must have a horsepower rating equal to or higher than the motor's horsepower rating.
Which one of the following is true about molded case switches used as motor controllers, as mentioned in the text?
Molded case switches are permitted as motor disconnecting means.
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?
The motor controller must have an ampere rating not less than twice the full-load current rating of the motor.
Which one of the following is true about motor controllers with a straight voltage rating and a slash rating, as mentioned in the text?
Motor controllers with a slash rating can be applied in circuits with any nominal voltage between conductors.
Quiz: Short-Circuit and Ground-Fault Protection Requirements for Branch Circuits and Feeders Test your knowledge of the NEC requirement for short-circuit and ground-fault protection in branch circuits and feeders. Learn about conductor sizing, ampacity, and proper protection for motors and other loads.
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