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One Horsepower or Less, Automatically Started. Any motor of 1 hp or less that is started automatically shall be protected against overload by one of the following means. Separate Overload Device. By a separate overload device following the requirements of 430.32(A)(1). For a multispeed motor, ea...

One Horsepower or Less, Automatically Started. Any motor of 1 hp or less that is started automatically shall be protected against overload by one of the following means. Separate Overload Device. By a separate overload device following the requirements of 430.32(A)(1). For a multispeed motor, each winding connection shall be considered separately. Modification of this value shall be permitted as provided in 430.32(C). Thermal Protector or Electronically Protected. A thermal protector integral with the motor shall be approved for use with the motor that it protects on the basis that it will prevent dangerous overheating of the motor due to overload and failure to start. An electronically protected motor shall be approved for use on the basis that it will prevent dangerous overheating due to the failure of the electronic control, overload, or failure to start the motor. Where the motor current-interrupting device is separate from the motor and its control circuit is operated by a protective device integral with the motor, it shall be arranged so that the opening of the control circuit results in interruption of current to the motor. Integral with Motor. A protective device integral with a motor that protects the motor against damage due to failure to start shall be permitted (1) if the motor is part of an approved assembly that does not subject the motor to overloads, or (2) if the assembly is also equipped with other safety controls (such as the safety combustion controls on a domestic oil burner) that protect the motor against damage due to failure to start. Where the assembly has safety controls that protect the motor, it shall be so indicated on the nameplate of the assembly where it will be visible after installation. Impedance-Protected. If the impedance of the motor windings is sufficient to prevent overheating due to failure to start, the motor shall be permitted to be protected as specified in 430.32(D)(2)a. for manually started motors if the motor is part of an approved assembly in which the motor will limit itself so that it will not be dangerously overheated. Informational Note: Many ac motors of less than 1⁄20 hp, such as clock motors, series motors, and so forth, and also some larger motors such as torque motors, come within this classification. It does not include split-phase motors having automatic switches that disconnect the starting windings. (C) Selection of Overload Device. Where the sensing element or setting or sizing of the overload device selected in accordance with 430.32(A)(1) and 430.32(B)(1) is not sufficient to start the motor or to carry the load, higher size sensing elements or incremental settings or sizing shall be permitted to be used, provided the trip current of the overload device does not exceed the following percentage of motor nameplate full-load current rating: Motors with marked service factor 1.15 or greater 140% Motors with a marked temperature rise 40°C or less 140% All other motors 130% If not shunted during the starting period of the motor as provided in 430.35, the overload device shall have sufficient time delay to permit the motor to start and accelerate its load. Informational Note: A Class 20 overload relay will provide a longer motor acceleration time than a Class 10 or Class 10A overload relay. A Class 30 overload relay will provide a longer motor acceleration time than a Class 20 overload relay. Use of a higher class overload relay may preclude the need for selection of a higher trip current. (D) One Horsepower or Less, Nonautomatically Started. (1) Permanently Installed. Overload protection shall be in accordance with 430.32(B). Not Permanently Installed. Within Sight from Controller. Overload protection shall be permitted to be furnished by the branch-circuit short-circuit and ground-fault protective device; such device, however, shall not be larger than that specified in Part IV of Article 430. Exception: Any such motor shall be permitted on a nominal 120-volt branch circuit protected at not over 20 amperes. Not Within Sight from Controller. Overload protection shall be in accordance with 430.32(B). Wound-Rotor Secondaries. The secondary circuits of wound-rotor ac motors, including conductors, controllers, resistors, and so forth, shall be permitted to be protected against overload by the motor-overload device. 430.33 Intermittent and Similar Duty. A motor used for a condition of service that is inherently short-time, intermittent, periodic, or varying duty, as illustrated by Table 430.22(E), shall be permitted to be protected against overload by the branch-circuit short-circuit and ground-fault protective device, provided the protective device rating or setting does not exceed that specified in Table 430.52(C)(1). Any motor application shall be considered to be for continuous duty unless the nature of the apparatus it drives is such that the motor cannot operate continuously with load under any condition of use. ENHANCED CONTENT Collapse Because duty-cycle service motors (short-time, intermittent, periodic, or varying) do not operate continuously, prolonged overloads are rare unless mechanical failure in the driven apparatus stalls the motor, in which case, the branch-circuit protective device would open the circuit. The omission of overload protective devices for such motors is based on the type of duty not on the time rating of the motor. 430.35 Shunting During Starting Period. (A) Nonautomatically Started. For a nonautomatically started motor, the overload protection shall be permitted to be shunted or cut out of the circuit during the starting period of the motor if the device by which the overload protection is shunted or cut out cannot be left in the starting position and if fuses or inverse time circuit breakers rated or set at not over 400 percent of the full-load current of the motor are located in the circuit so as to be operative during the starting period of the motor. Automatically Started. The motor overload protection shall not be shunted or cut out during the starting period if the motor is automatically started. Exception: The motor overload protection shall be permitted to be shunted or cut out during the starting period on an automatically started motor where the following apply: (1) The motor starting period exceeds the time delay of available motor overload protective devices, and (2) Listed means are provided to perform the following: a. Sense motor rotation and automatically prevent the shunting or cutout in the event that the motor fails to start, and b. Limit the time of overload protection shunting or cutout to less than the locked rotor time rating of the protected motor, and c. Provide for shutdown and manual restart if motor running condition is not reached. 430.36 Fuses — In Which Conductor. Where fuses are used for motor overload protection, a fuse shall be inserted in each ungrounded conductor and also in the grounded conductor if the supply system is 3-wire, 3-phase ac with one conductor grounded. 430.37 Devices Other Than Fuses — In Which Conductor. Where devices other than fuses are used for motor overload protection, Table 430.37 shall govern the minimum allowable number and location of overload units such as trip coils or relays. Table 430.37 Overload Units Kind of Motor Supply System Number and Location of Overload Units, Such as Trip Coils or Relays 1-phase ac or dc 2-wire, 1-phase ac or dc ungrounded 1 in either conductor 1-phase ac or dc 2-wire, 1-phase ac or dc, one conductor grounded 1 in ungrounded conductor 1-phase ac or dc 3-wire, 1-phase ac or dc, grounded neutral conductor 1 in either ungrounded conductor 1-phase ac Any 3-phase 1 in ungrounded conductor 2-phase ac 3-wire, 2-phase ac, ungrounded 2, one in each phase 2-phase ac 3-wire, 2-phase ac, one conductor grounded 2 in ungrounded conductors 2-phase ac 4-wire, 2-phase ac, grounded or ungrounded 2, one for each phase in ungrounded conductors 2-phase ac Grounded neutral or 5-wire, 2-phase ac, ungrounded 2, one for each phase in any ungrounded phase wire 3-phase ac Any 3-phase 3, one in each phase Exception: An overload unit in each phase shall not be required where overload protection is provided by other approved means. ENHANCED CONTENT Collapse All 3-phase motors, except those protected by other approved means, must be provided with three overload units, one in each phase. Examples of those motors protected by other means include specially designed or integral-type detectors, with or without supplementary external protective devices. 430.38 Number of Conductors Opened by Overload Device. Motor overload devices, other than fuses or thermal protectors, shall simultaneously open a sufficient number of ungrounded conductors to interrupt current flow to the motor. 430.39 Motor Controller as Overload Protection. A motor controller shall also be permitted to serve as an overload device if the number of overload units complies with Table 430.37 and if these units are operative in both the starting and running position in the case of a dc motor, and in the running position in the case of an ac motor. 430.40 Overload Relays. Overload relays and other devices for motor overload protection that are not capable of opening short circuits or ground faults shall be protected by fuses or circuit breakers with ratings or settings in accordance with 430.52 or by a motor short-circuit protector in accordance with 430.52. Exception: Where approved for group installation and marked to indicate the maximum size of fuse or inverse time circuit breaker by which they must be protected, the overload devices shall be protected in accordance with this marking. ENHANCED CONTENT Collapse Some overload devices are marked with a maximum short-circuit and ground-fault protective device rating or setting. This rating sets the limit on the maximum rating or setting of a fuse or a circuit breaker that may be upstream from the overload device. The rating also notifies the user that coordination between the overload device and the short-circuit and ground-fault device is required, which is most often the case for group motor installation. 430.42 Motors on General-Purpose Branch Circuits. Overload protection for motors used on general-purpose branch circuits shall be provided as specified in 430.42(A), (B), (C), or (D). Not Over 1 Horsepower. One or more motors without individual overload protection shall be permitted to be connected to a general-purpose branch circuit only where the installation complies with the limiting conditions specified in 430.32(B), 430.32(D), and 430.53(A)(1) and (A)(2). Over 1 Horsepower. Motors of ratings larger than specified in 430.53(A) shall be permitted to be connected to general-purpose branch circuits only where each motor is protected by overload protection selected to protect the motor as specified in 430.32. Both the motor controller and the motor overload device shall be approved for group installation with the short-circuit and ground-fault protective device selected in accordance with 430.53. Cord-and-Plug-Connected. Where a motor is connected to a branch circuit by means of an attachment plug and a receptacle or cord connector, and individual overload protection is omitted in accordance with 430.42(A), the rating of the attachment plug and receptacle or cord connector shall not exceed 15 amperes at 125 volts or 250 volts. Where individual overload protection is required in accordance with 430.42(B) for a motor or motor-operated appliance that is attached to the branch circuit through an attachment plug and a receptacle or cord connector, the overload device shall be an integral part of the motor or appliance. The rating of the attachment plug and receptacle or cord connector shall determine the rating of the circuit to which the motor can be connected, in accordance with 210.21(B). Time Delay. The branch-circuit short-circuit and ground-fault protective device protecting a circuit to which a motor or motor-operated appliance is connected shall have sufficient time delay to permit the motor to start and accelerate its load. 430.43 Automatic Restarting. A motor overload device that can restart a motor automatically after overload tripping shall not be installed unless approved for use with the motor it protects. A motor overload device that can restart a motor automatically after overload tripping shall not be installed if automatic restarting of the motor can result in injury to persons. 430.44 Orderly Shutdown. If immediate automatic shutdown of a motor by a motor overload protective device(s) would introduce additional or increased hazard(s) to a person(s) and continued motor operation is necessary for safe shutdown of equipment or process, a motor overload sensing device(s) complying with Part III of this article shall be permitted to be connected to a supervised alarm instead of causing immediate interruption of the motor circuit, so that corrective action or an orderly shutdown can be initiated. Part IV. Motor Branch-Circuit Short-Circuit and Ground-Fault Protection 430.51 General. Part IV specifies devices intended to protect the motor branch-circuit conductors, the motor control apparatus, and the motors against overcurrent due to short circuits or ground faults. The devices specified in Part IV do not include the types of devices required by 210.8, 230.95, and 590.6. Informational Note No. 1: See Informative Annex D, Example D8, for an example of motor branch-circuit short-circuit and ground-fault protection selection. Part IV shall not apply to motor circuits rated over 1000 volts, nominal. Informational Note No. 2: See Part XI for over 1000 volts, nominal. ENHANCED CONTENT Collapse The rules for short-circuit and ground-fault protection are specific for particular situations. A short circuit is a fault between two or more circuit conductors. A ground fault is a fault between an ungrounded conductor and ground. During a short-circuit or ground-fault condition, the extremely high current causes the protective device (typically fuses or circuit breakers in systems rated 600 volts and less) to open the circuit. Excessive current caused by an overload condition passes through the overload protective device at the motor controller, thereby causing the device to open the control-circuit or motor-circuit conductors. For small motors, a fuse or circuit breaker may be sized so that it provides all the required overcurrent (short-circuit, ground-fault, and overload) protection for the motor and motor circuit components. The single protective device must meet the applicable requirements of Parts III and IV. 430.52 Rating or Setting for Individual Motor Circuit. (A) General. The motor branch-circuit short-circuit and ground-fault protective device shall comply with 430.52(B) and either 430.52(C) or (D), as applicable. ENHANCED CONTENT Collapse For certain exceptions to the maximum rating or setting of these motor branch-circuit protective devices, as specified in Table 430.52(C)(1), see 430.52, 430.53, and 430.54. In general, 430.6 requires the values given in Tables 430.247 through 430.250 (including notes) to be used instead of the actual motor nameplate current rating to determine the ampacity of conductors or ampere ratings of switches, branch-circuit overcurrent devices, and so forth. Separate motor overload protection must be based on the motor nameplate current rating. The exhibit below illustrates a typical motor circuit in which the branch-circuit short-circuit and ground-fault protective fuse or circuit breaker rating must carry the starting current and may be sized 150 to 300 percent of the motor full-load current (depending on the type of motor). Section 430.52 could result in a branch-circuit and ground-fault protective device rating higher than the ampacity of the motor circuit conductors. See also 430.22 and its enhanced content for sizing motor circuit conductors. The selected rating or setting of the branch-circuit short-circuit and ground-fault protective device should be as low as possible for maximum protection. However, if the rating or setting specified in Table 430.52(C)(1) or permitted by 430.52(C)(1)(a) is not sufficient for the starting current of the motor, a higher rating or setting is allowed per 430.52(C)(1)(b). For example, a higher rating would be allowed for a motor under severe starting conditions in which the motor and its driven machinery require an extended length of time to reach the desired speed. All Motors. The motor branch-circuit short-circuit and ground-fault protective device shall be capable of carrying the starting current of the motor. Rating or Setting. In Accordance with Table 430.52(C)(1). A protective device that has a rating or setting not exceeding the value calculated according to the values given in Table 430.52(C)(1) shall be used unless otherwise permitted in 430.52(C)(1)(a) or (C)(1)(b). Table 430.52(C)(1) Maximum Rating or Setting of Motor Branch-Circuit Short-Circuit and Ground-Fault Protective Devices Type of Motor Percentage of Full-Load Current Nontime Delay Fuse1 Dual Element (Time-Delay) Fuse1 Instantaneous -Trip Breaker Inverse Time Breaker2 Single-phase motors 300 175 800 250 AC polyphase motors other than wound-rotor 300 175 800 250 Squirrel cage — other than Design B energy-efficient — and Design B premium efficiency 300 175 800 250 Design B energy-efficient and Design B premium efficiency 300 175 1100 250 Synchronous3 300 175 800 250 Wound-rotor 150 150 800 150 DC (constant voltage) 150 150 250 150 Note: See 430.54 for certain exceptions to the values specified. 1The values in the Nontime Delay Fuse column apply to time-delay Class CC fuses. 2The values given in the last column also cover the ratings of nonadjustable inverse time types of circuit breakers that can be modified as in 430.52(C)(1)(a) and (C)(1)(b). 3Synchronous motors of the low-torque, low-speed type (usually 450 rpm or lower), such as those used to drive reciprocating compressors, pumps, and so forth, that start unloaded, do not require a fuse rating or circuit-breaker setting in excess of 200 percent of full-load current. Where the values as determined by Table 430.52(C)(1) do not correspond to the standard ampere ratings and settings provided in 240.6, the next higher standard rating or setting shall be permitted. Where the rating specified in Table 430.52(C)(1), or the rating modified by 430.52(C)(1)(a), is not sufficient for the starting current of the motor, any of the following shall apply: The rating of a nontime-delay fuse not exceeding 600 amperes or a time-delay Class CC fuse shall be permitted to be increased but shall in no case exceed 400 percent of the full-load current. The rating of a time-delay (dual-element) fuse shall be permitted to be increased but shall in no case exceed 225 percent of the full-load current. The rating of an inverse time circuit breaker shall be permitted to be increased but shall in no case exceed 400 percent for full-load currents of 100 amperes or less or 300 percent for full-load currents greater than 100 amperes. The rating of a fuse of 601–6000 ampere classification shall be permitted to be increased but shall in no case exceed 300 percent of the full-load current. Informational Note: See Informative Annex D, Example D8, for an example of motor branch-circuit short-circuit and ground-fault rating and setting and Informational Note Figure 430.1 for an example location. ENHANCED CONTENT Collapse Class CC fuses are current-limiting fuses that may also be marked as “time delay,” which indicates that the fuse has been investigated in accordance with the time-delay requirements of the standard. Class CC fuses are permitted to be sized according to the requirements of non-time-delay-rated fuses because they are fast-acting. Examples of Class CC fuses are shown below. (Courtesy of Eaton, Bussmann Division) Overload Relay Table. Where maximum branch-circuit short-circuit and ground-fault protective device ratings are shown in the manufacturer’s overload relay table for use with a motor controller or are otherwise marked on the equipment, they shall not be exceeded even if higher values are allowed as shown above. Instantaneous-Trip Circuit Breaker. An instantaneous-trip circuit breaker shall be permitted if the conditions of 430.52(C)(3)(a) and (C)(3)(b) are met. Application. Instantaneous-trip circuit breakers shall be adjustable and part of a listed combination motor controller having coordinated motor overload and short-circuit and ground-fault protection in each conductor. Informational Note No. 1: Instantaneous-trip circuit breakers are also known as motor-circuit protectors (MCPs). Informational Note No. 2: For the purpose of this article, instantaneous-trip circuit breakers could include a damping means to accommodate a transient motor inrush current without nuisance tripping of the circuit breaker. (b) Setting. The instantaneous-trip circuit breaker shall be adjusted to a setting in accordance with one of the following: (1) No greater than the value specified in Table 430.52(C)(1) Where the value specified in Table 430.52(C)(1) is not sufficient for the starting current of the motor, one of the following settings shall be permitted: Motors other than design B energy-efficient and Design B premium efficiency motors shall be permitted to be increased but shall in no case exceed 1300 percent of the motor full-load current. Design B energy-efficient and Design B premium efficiency motors shall be permitted to be increased but shall in no case exceed 1700 percent of the motor full-load current. Where an engineering analysis determines the value is not sufficient for the starting current of the motor, it shall not be necessary to first apply the value specified in Table 430.52(C)(1). Informational Note No. 3: See NEMA MG 1-2016, Motors and Generators, Part 12.59 for additional information on the requirements for a motor to be classified “energy efficient.” Where the motor full-load current is 8 amperes or less, the setting of the instantaneous-trip circuit breaker with a continuous current rating of 15 amperes or less in a listed combination motor controller that provides coordinated motor branch-circuit overload and short-circuit and ground-fault protection shall be permitted to be increased to the value marked on the motor controller. Multispeed Motor. For a multispeed motor, a single short-circuit and ground-fault protective device shall be permitted for two or more windings of the motor if the rating of the protective device does not exceed the above applicable percentage of the nameplate rating of the smallest winding protected. Exception: For a multispeed motor, a single short-circuit and ground-fault protective device shall be permitted to be used and sized according to the full-load current of the highest current winding, where all of the following conditions are met: (1) Each winding is equipped with individual overload protection sized according to its full-load current. (2) The branch-circuit conductors supplying each winding are sized according to the full-load current of the highest full-load current winding. (3) The motor controller for each winding has a horsepower rating not less than that required for the winding having the highest horsepower rating. (5) Power Electronic Devices. Semiconductor fuses intended for the protection of electronic devices shall be permitted in lieu of devices listed in Table 430.52(C)(1) for power electronic devices, associated electromechanical devices (such as bypass contactors and isolation contactors), and conductors in a solid-state motor controller system if the marking for replacement fuses is provided adjacent to the fuses. Self-