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otor current shall be assumed to be six times the full-load current. ENHANCED CONTENT Collapse Listed circuit breakers and molded case switches are tested under overload conditions at six times their rating, to cover motor circuit applications, and are suitable for use as a motor disconnecting means...

otor current shall be assumed to be six times the full-load current. ENHANCED CONTENT Collapse Listed circuit breakers and molded case switches are tested under overload conditions at six times their rating, to cover motor circuit applications, and are suitable for use as a motor disconnecting means. 430.111 Switch or Circuit Breaker as Both Motor Controller and Disconnecting Means. A switch or circuit breaker shall be permitted to be used as both the motor controller and disconnecting means if it complies with 430.111(A) and is one of the types specified in 430.111(B). General. The switch or circuit breaker complies with the requirements for motor controllers specified in 430.83, opens all ungrounded conductors to the motor, and is protected by an overcurrent device in each ungrounded conductor (which shall be permitted to be the branch-circuit fuses). The overcurrent device protecting the motor controller shall be permitted to be part of the motor controller assembly or shall be permitted to be separate. An autotransformer-type motor controller shall be provided with a separate disconnecting means. Type. The device shall be one of the types specified in 430.111(B)(1), (B)(2), or (B)(3). Air-Break Switch. An air-break switch, operable directly by applying the hand to a lever or handle. Inverse Time Circuit Breaker. An inverse time circuit breaker operable directly by applying the hand to a lever or handle. The circuit breaker shall be permitted to be both power-operable and manually operable. Oil Switch. An oil switch used on a circuit whose rating does not exceed 1000 volts or 100 amperes, or by special permission on a circuit exceeding this capacity where under expert supervision. The oil switch shall be permitted to be both power-operable and manually operable. ENHANCED CONTENT Collapse If used as a controller, a switch or circuit breaker must meet all the requirements for controllers and be protected by branch-circuit short-circuit and ground-fault protective devices (fuses or a circuit breaker), which ensure that all ungrounded conductors will be opened. If the controller consists of a manually operable air-break switch, an inverse time circuit breaker, or a 100-ampere maximum oil switch (higher rating by special permission), the controller is considered a satisfactory disconnecting means. The intent of 430.111 is to permit omission of an additional device to serve as a disconnecting means. A separate disconnecting means must be provided if the controller is of the autotransformer. (This switch can be combined in the same enclosure with a motor overload protective device.) 430.112 Motors Served by Single Disconnecting Means. Each motor shall be provided with an individual disconnecting means. Exception: A single disconnecting means shall be permitted to serve a group of motors under any one of the conditions of (1), (2), and (3). The single disconnecting means shall be rated in accordance with 430.110(C). (1) Where a number of motors drive several parts of a single machine or piece of apparatus, such as metal- and woodworking machines, cranes, and hoists. (2) Where a group of motors is under the protection of one set of branch-circuit protective devices as permitted by 430.53(A). (3) Where a group of motors is in a single room within sight from the location of the disconnecting means. ENHANCED CONTENT Collapse A single disconnecting means must have a rating equal to the sum of the horsepower or current of each motor in the group. If the sum is over 2 horsepower, a motor circuit switch (horsepower-rated) must be used; thus, for five 2-horsepower motors, the disconnecting means should be a motor-circuit switch rated at not less than 10 horsepower. Part (1) of the exception indicates that a single disconnecting means may be used where a number of motors drive several parts of a single machine, such as cranes (see 610.31 through 610.33), metal or woodworking machines, steel rolling mill machinery, and so forth. The single disconnecting means for multi-motor machinery provides a positive means of simultaneously de-energizing all motor branch circuits, including remote-control circuits, interlocking circuits, limit-switch circuits, and operator control stations. Part (2) of the exception refers to 430.53(A), which permits a group of motors under the protection of the same branch-circuit device, provided the device is rated not more than 20 amperes on a nominal 120-volt branch circuit, or not over 15 amperes on a branch circuit of 1000 volts, nominal or less. The motors must be rated 1 horsepower or less, and the full-load current for each motor is not permitted to exceed 6 amperes. A single disconnecting means is both practical and economical for a group of such small motors. Part (3) of the exception covers the common situation in which a group of motors is in one room, such as a pump room, compressor room, or mixer room. It is possible to design the layout of a single disconnecting means with an unobstructed view from each motor. (See the definition of in sight from in Article 100.) These conditions for an individual disconnecting means are like those specified in 430.87, which permits the use of a single controller for a group of motors. 430.113 Energy from More Than One Source. Motor and motor-operated equipment receiving electric energy from more than one source shall be provided with disconnecting means from each source of electric energy immediately adjacent to the equipment served. Each source shall be permitted to have a separate disconnecting means. Where multiple disconnecting means are provided, a permanent warning sign shall be provided on or adjacent to each disconnecting means indicating that multiple sources must be shut off to remove all power to the equipment. The sign at each disconnect shall identify the other specific circuits. Exception No. 1: Where a motor receives electric energy from more than one source, the disconnecting means for the main power supply to the motor shall not be required to be immediately adjacent to the motor if the motor controller disconnecting means is lockable in accordance with 110.25. Exception No. 2: A separate disconnecting means shall not be required for a Class 2 remote-control circuit complying with Parts I and II of Article 725, rated not more than 30 volts, and isolated and ungrounded. ENHANCED CONTENT Collapse Some motors require multiple separate sources of power to operate properly, such as a motor space heater or a speed switch. Synchronous motors commonly use dc power for excitation purposes. Section 430.113 could also apply to circuits that supply power to speed or vibration sensors mounted within or otherwise attached to the motor. Where the individual sources have multiple disconnecting means, a permanent warning sign is required to warn the user that other power sources are present. Exception No. 2 removes the disconnect requirement only for Class 2 circuits. Part X. Adjustable-Speed Drive Systems 430.120 General. The installation requirements for Part I through Part IX are applicable unless modified or supplemented by Part X. Power conversion equipment used in adjustable-speed drive systems shall comply with Part X for an input or output rated 1000 volts or lower and with Part XI for an input or output rated over 1000 volts. ENHANCED CONTENT Collapse Adjustable-speed drives are used extensively in commercial, institutional, and industrial motor applications. The exhibit below shows 480-volt adjustable-speed drives, also known as variable-frequency drives (VFDs), for air-handling units. (Courtesy of International Association of Electrical Inspectors) Part X consolidates requirements that are unique to these drives, which include rules regarding methods of overtemperature protection in motors (see 430.126). This is a critical area, because motors operating at reduced speed do not provide adequate air circulation over windings from a fan integral with the motor. An overload device that actuates on current exceeding full-load amperes will not operate, because the operating current at slower speeds is reduced. A thermal-sensing device integral with the motor will sense a temperature rise in the motor windings. 430.122 Conductors — Minimum Size and Ampacity. (A) Branch/Feeder Circuit Conductors. Circuit conductors supplying power conversion equipment included as part of an adjustable-speed drive system shall have an ampacity not less than 125 percent of the rated input current to the power conversion equipment. Informational Note: Power conversion equipment can have multiple power ratings and corresponding input currents. Output Conductors. The conductors between the power conversion equipment and the motor shall have an ampacity equal to or larger than 125 percent of the motor full-load current as determined by 430.6(A) or (B). Exception: If the power conversion equipment is listed and marked as “Suitable for Output Motor Conductor Protection,” the conductor between the power conversion equipment and the motor shall have an ampacity equal to or greater than the larger of the following: (1) 125 percent of the motor full-load current as determined by 430.6(A) or (B) (2) The ampacity of the minimum conductor size marked on the power conversion equipment Informational Note No. 1: See 430.130 and 430.131 for branch circuit protection requirements. The minimum ampacity required of output conductors is often different than that of the conductors supplying the power conversion equipment. Informational Note No. 2: Circuit conductors on the output of an adjustable-speed drive system are susceptible to breakdown under certain conditions due to the characteristics of the output waveform of the drive. Factors affecting the conductors include, but are not limited to, the output voltage, frequency, and current; the length of the conductors; the spacing between the conductors; and the dielectric strength of the conductor insulation. Methods to mitigate breakdown include consideration of one or more of these factors. ENHANCED CONTENT Collapse Where an adjustable-speed drive system is used in a motor circuit, two sets of branch-circuit conductors must be considered in respect to minimum size. The basis for sizing the branch-circuit conductors supplying the power conversion equipment is the input current rating of that unit. That portion of the branch circuit from the power conversion equipment to the motor (i.e., output conductors) uses the general motor branch-circuit approach, and the currents found in the Article 430 tables are the basis used for sizing. Both the input conductors and the output conductors are required to be sized by applying 125 percent to the conductor sizing parameter specified in 430.122(A) and (B). Bypass Device. The ampacity of circuit conductors supplying power conversion equipment included as part of an adjustable-speed drive system that utilizes a bypass device shall be the larger of either of the following: 125 percent of the rated input current to the power conversion equipment 125 percent of the motor full-load current rating determined in accordance with 430.6 Several Motors or a Motor and Other Loads. Conductors supplying several motors or a motor and other loads, including power conversion equipment, shall have ampacity in accordance with 430.24, using the rated input current of the power conversion equipment for purposes of calculating ampacity. 430.124 Overload Protection. Overload protection of the motor shall be provided. Included in Power Conversion Equipment. Where the power conversion equipment is marked to indicate that motor overload protection is included, additional overload protection shall not be required. Bypass Circuits. For adjustable-speed drive systems that utilize a bypass device to allow motor operation at rated full-load speed, motor overload protection as described in Article 430, Part III, shall be provided in the bypass circuit. Multiple Motor Applications. For multiple motor application, individual motor overload protection shall be provided in accordance with Article 430, Part III. 430.126 Motor Overtemperature Protection. (A) General. Adjustable-speed drive systems shall protect against motor overtemperature conditions where the motor is not rated to operate at the nameplate rated current over the speed range required by the application. This protection shall be provided in addition to the conductor protection required in 430.32. Protection shall be provided by one of the following means: Motor thermal protector in accordance with 430.32 Adjustable-speed drive system with load and speed-sensitive overload protection and thermal memory retention upon shutdown or power loss Exception to (2): Thermal memory retention upon shutdown or power loss is not required for continuous duty loads. Overtemperature protection relay utilizing thermal sensors embedded in the motor and meeting the requirements of 430.126(A)(2) Thermal sensor embedded in the motor whose communications are received and acted upon by an adjustable-speed drive system Informational Note: The relationship between motor current and motor temperature changes when the motor is operated by an adjustable-speed drive. In certain applications, overheating of motors can occur when operated at reduced speed, even at current levels less than a motor’s rated full-load current. The overheating can be the result of reduced motor cooling when its shaft-mounted fan is operating less than rated nameplate RPM. As part of the analysis to determine whether overheating will occur, it is necessary to consider the continuous torque capability curves for the motor given the application requirements. This will assist in determining whether the motor overload protection will be able, on its own, to provide protection against overheating. These overheating protection requirements are only intended to apply to applications where an adjustable-speed drive, as defined in Article 100, is used. For motors that utilize external forced air or liquid cooling systems, overtemperature can occur if the cooling system is not operating. Although this issue is not unique to adjustable speed applications, externally cooled motors are most often encountered with such applications. In these instances, overtemperature protection using direct temperature sensing is recommended [i.e., 430.126(A)(1), (A)(3), or (A)(4)], or additional means should be provided to ensure that the cooling system is operating (flow or pressure sensing, interlocking of adjustable-speed drive system and cooling system, etc.). (B) Multiple Motor Applications. For multiple motor applications, individual motor overtemperature protection shall be provided as required in 430.126(A). Automatic Restarting and Orderly Shutdown. 430.43 and 430.44 shall apply to the motor overtemperature protection means. 430.128 Disconnecting Means. The disconnecting means shall be permitted to be in the incoming line to the conversion equipment and shall have a rating not less than 115 percent of the rated input current of the conversion unit. 430.130 Branch-Circuit Short-Circuit and Ground-Fault Protection for Single Motor Circuits Containing Power Conversion Equipment. (A) Circuits Containing Power Conversion Equipment. Circuits containing power conversion equipment shall be protected by a branch-circuit short-circuit and ground-fault protective device in accordance with all of the following: (1) The rating and type of protection shall be determined by 430.52(C)(1), (C)(3), (C)(5), or (C)(6), using the full-load current rating of the motor load as determined by 430.6(A) or (B). Exception to (1): The rating and type of protection shall be permitted to be determined by Table 430.52(C)(1) using the power conversion equipment’s rated input current where the power conversion equipment is listed and marked “Suitable for Output Motor Conductor Protection.” Informational Note No. 1: Motor conductor branch-circuit short-circuit and ground-fault protection from the power conversion equipment to the motor is provided by power conversion equipment that is listed and marked “Suitable for Output Motor Conductor Protection.” Informational Note No. 2: A motor branch circuit using power conversion equipment, including equipment listed and marked “Suitable for Output Motor Conductor Protection,” includes the input circuit to the power conversion equipment. (2) Where maximum branch-circuit short-circuit and ground-fault protective ratings are stipulated for specific device types in the manufacturer’s instructions for the power conversion equipment or are otherwise marked on the equipment, they shall not be exceeded even if higher values are permitted by 430.130(A)(1). A self-protected combination motor controller shall only be permitted where specifically identified in the manufacturer’s instructions for the power conversion equipment or if otherwise marked on the equipment. Informational Note No. 3: The type of protective device, its rating, and its setting are often marked on or provided with the power conversion equipment. (4) Where an instantaneous-trip circuit breaker or semiconductor fuses are permitted in accordance with the drive manufacturer’s instructions for use as the branch-circuit short-circuit and ground-fault protective device for listed power conversion equipment, they shall be provided as an integral part of a single listed assembly incorporating both the protective device and power conversion equipment. Bypass Circuit/Device. Branch-circuit short-circuit and ground-fault protection shall also be provided for a bypass circuit/device(s). Where a single branch-circuit short-circuit and ground-fault protective device is provided for circuits containing both power conversion equipment and a bypass circuit, the branch-circuit protective device type and its rating or setting shall be in accordance with those determined for the power conversion equipment and for the bypass circuit/device(s) equipment. 430.131 Several Motors or Loads on One Branch Circuit Including Power Conversion Equipment. For installations meeting all the requirements of 430.53 that include one or more power converters, the branch-circuit short-circuit and ground-fault protective fuses or inverse time circuit breakers shall be of a type and rating or setting permitted for use with the power conversion equipment using the full-load current rating of the connected motor load in accordance with 430.53. For the purposes of 430.53 and 430.131, power conversion equipment shall be considered to be a motor controller. Part XI. Over 1000 Volts, Nominal 430.201 General. Part XI recognizes the additional hazard due to the use of higher voltages. It adds to or amends the other provisions of this article. 430.202 Marking on Motor Controllers. In addition to the marking required by 430.8, a motor controller shall be marked with the control voltage. 430.203 Raceway Connection to Motors. Flexible metal conduit or liquidtight flexible metal conduit not exceeding 1.8 m (6 ft) in length shall be permitted to be employed for raceway connection to a motor terminal enclosure. 430.204 Wire-Bending Space in Enclosures. Motor controllers rated over 1000 volts shall provide wire-bending space within the enclosure for conductors installed in accordance with 305.5. 430.205 Size of Conductors. The ampacities of conductors supplying equipment rated over 1000 volts, nominal, shall be determined in accordance with 315.60or 430.205(A) and (B). General Motor Systems. Conductors supplying motors shall be sized not less than the current trip setting of the motor overload protective device(s). Adjustable-Speed Drive Systems. For an adjustable-speed drive system, the conductors supplying the power conversion equipment shall have an ampacity not less than 125 percent of the rated input current to the power conversion equipment. 430.206 Motor-Circuit Overcurrent Protection. (A) General. Each motor circuit shall include coordinated protection to automatically interrupt overload and fault currents in the motor, the motor-circuit conductors, and the motor control apparatus. Adjustable-speed drive systems with input or output voltages over 1000 volts, nominal, shall comply with 430.124 and 430.126. All other motors shall comply with 430.206(B) through (C). Exception: Where a motor is critical to an operation and the motor should operate to failure if necessary to prevent a greater hazard to persons, the sensing device(s) shall be permitted to be connected to a supervised annunciator or alarm instead of interrupting the motor circuit. (B) Overload Protection. (1) Type of Overload Device. Each motor shall be protected against dangerous heating due to motor overloads and failure to start by a thermal protector integral with the motor or external current-sensing devices, or both. Protective device settings for each motor circuit shall be determined under engineering supervision. ENHANCED CONTENT Collapse Selecting the proper overload and short-circuit protection for medium-voltage motor circuits is more complex than for low-voltage circuits. For medium-voltage motor circuits, it is critical for the overload relay to coordinate with the short-circuit protection, because some short-circuit protective devices cannot safely open below certain multiples of their rating. In these overload cases, the overload relay must open before the short-circuit protective device is asked to open. At the same time, the overload relay might not safely open beyond certain multiples of its rating, requiring the short-circuit protective device to open. The curves of both the overload relay and the short-circuit protective device must be correlated to ensure that each opens only on levels of current for which it can safely open. Wound-Rotor Alternating-Current Motors. The secondary circuits of wound-rotor ac motors, including conductors, motor controllers, and resistors rated for the application, shall be considered as protected against overcurrent by the motor overload protection means. Operation. Operation of the overload interrupting device shall simultaneously disconnect all ungrounded conductors. Automatic Reset. Overload sensing devices shall not automatically reset after trip unless resetting of the overload sensing device does not cause automatic restarting of the motor or there is no hazard to persons created by automatic restarting of the motor and its connected machinery. Fault-Current Protection. Type of Protection. Fault-current protection shall be provided in each motor circuit as specified by either 430.206(C)(1)(a) or (C)(1)(b). A circuit breaker of suitable type and rating arranged so that it can be serviced without hazard. The circuit breaker shall simultaneously disconnect all ungrounded conductors. The circuit breaker shall be permitted to sense the fault current by means of integral or external sensing elements. Fuses of a suitable type and rating placed in each ungrounded conductor. Fuses shall be used with suitable disconnecting means, or they shall be of a type that can also serve as the disconnecting means. They shall be arranged so that they cannot be serviced while they are energized. Reclosing. Fault-current interrupting devices shall not automatically reclose the circuit. Exception: Automatic reclosing of a circuit shall be permitted where the circuit is exposed to transient faults and where such automatic reclosing does not create a hazard to persons. (3) Combination Protection. Overload protection and fault-current protection shall be permitted to be provided by the same device. 430.207 Rating of Motor Control Apparatus. The ultimate trip current of overcurrent (overload) relays or other motor-protective devices used shall not exceed 115 percent of the motor controller’s continuous current rating. Where the motor branch-circuit disconnecting means is separate from the motor controller, the disconnecting means current rating shall not be less than the ultimate trip setting of the overcurrent relays in the circuit. 430.208 Disconnecting Means. The motor controller disconnecting means shall be a switch or circuit breaker having a