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the conductors do not extend beyond the motor control equipment enclosure, the rating of the protective device(s) shall not exceed the value specified in Column B of Table 430.72(B)(2). Where the conductors extend beyond the motor control equipment enclosure, the rating of the protective device(s) s...

the conductors do not extend beyond the motor control equipment enclosure, the rating of the protective device(s) shall not exceed the value specified in Column B of Table 430.72(B)(2). Where the conductors extend beyond the motor control equipment enclosure, the rating of the protective device(s) shall not exceed the value specified in Column C of Table 430.72(B)(2). Table 430.72(B)(2) Maximum Rating of Overcurrent Protective Device in Amperes Column A Separate Protection Provided Protection Provided by Motor Branch-Circuit Protective Device(s) Column B Conductors Within Enclosure Column C Conductors Extend Beyond Enclosure Control Circuit Conductor Size (AWG) Copper Aluminum or Copper-Clad Aluminum Copper Aluminum or Copper-Clad Aluminum Copper Aluminum or Copper-Clad Aluminum 18 7 — 25 — 7 — 16 10 — 40 — 10 — 14 (Note 1) — 100 — 45 — 12 (Note 1) (Note 1) 120 100 60 45 10 (Note 1) (Note 1) 160 140 90 75 Larger than 10 (Note 1) (Note 1) (Note 2) (Note 2) (Note 3) (Note 3) Notes: Value specified in 310.15 as applicable. 400 percent of value specified in Table 310.17 for 60°C conductors. 300 percent of value specified in Table 310.16 for 60°C conductors. Control Circuit Transformer. Where a motor control circuit transformer is provided, the transformer shall be protected in accordance with 430.72(C)(1), (C)(2), (C)(3), (C)(4), or (C)(5). Exception: Overcurrent protection shall be omitted where the opening of the control circuit would create a hazard as, for example, the control circuit of a fire pump motor and the like. Class 1 Power-Limited, Class 2, or Class 3 Circuits. Where the transformer supplies a Class 1 power-limited circuit, the circuit shall comply with 724.30 through 724.52. Where the transformer supplies a Class 2 or Class 3 remote-control circuit, the circuit shall comply with the requirements of Part II of Article 725. Transformers. Protection shall be permitted to be provided in accordance with 450.3. Less Than 50 Volt-Amperes. Control circuit transformers rated less than 50 volt-amperes (VA) and that are an integral part of the motor controller and located within the motor controller enclosure shall be permitted to be protected by primary overcurrent devices, impedance limiting means, or other inherent protective means. Primary Less Than 2 Amperes. Where the control circuit transformer rated primary current is less than 2 amperes, an overcurrent device rated or set at not more than 500 percent of the rated primary current shall be permitted in the primary circuit. Other Means. Protection shall be permitted to be provided by other approved means. ENHANCED CONTENT Collapse Motor control circuits can receive their power either from the load side of the motor short-circuit and ground-fault protective device or from a separate source, such as a panelboard. Motor control circuits that receive their power from a separate source must be protected against overcurrent in accordance with 724.43 for Class 1 circuits. Conductor sizes 14 AWG and larger must be protected according to their ampacity listed in Tables 310.16 through 310.20. Conductor sizes 16 and 18 AWG must be protected at not more than 10 and 7 amperes, respectively, as specified in Table 430.72(B)(2). If a motor control circuit is tapped from the load side of the motor branch-circuit short-circuit and ground-fault protective device, the size of the tapped conductor and the rating of the overcurrent device are based on whether the conductor stays within the motor control enclosure or leaves it. The load on a motor control circuit is similar to a motor branch-circuit load in that there is a predetermined connected load. An initial high inrush of current also occurs until the armature of the relay is seated and the current decreases to a steady state. Therefore, the overcurrent protection is similar to the short-circuit and ground-fault protection provided for a motor and is allowed to be greater than the ampacity of the control circuit conductor. 430.73 Protection of Conductors from Physical Damage. Where damage to a motor control circuit would constitute a hazard, all conductors of such a remote motor control circuit that are outside the control device itself shall be installed in a raceway or be otherwise protected from physical damage. ENHANCED CONTENT Collapse If damage to the control circuit conductors could result in an accidental ground fault or short circuit, causing the device to operate or rendering the device inoperative (either condition could constitute a hazard to persons or property), conductors must be installed in a raceway. Where boilers or furnaces are equipped with an automatic safety control device, damage to the conductors of the low-voltage control circuit (e.g., a thermostat) does not constitute a hazard (see Article 725, Part II). 430.74 Electrical Arrangement of Control Circuits. Where one conductor of the motor control circuit is grounded, the motor control circuit shall be arranged so that a ground fault in the control circuit remote from the motor controller will (1) not start the motor and (2) not bypass manually operated shutdown devices or automatic safety shutdown devices. ENHANCED CONTENT Collapse The inadvertent grounding of control circuits is a significant safety issue. Section 430.74 requires that if one side of the motor control circuit is grounded, the circuit must be arranged so that a ground fault in the remote-control device will not start the motor. For example, in the control wiring illustrated below, the control circuit is a 120-volt, single-phase circuit derived from a 208-volt, 3-phase wye system supplying the motor, and one side of the control circuit is the grounded neutral. If the start button of the motor control circuit is connected to the grounded neutral, a ground fault on the coil side of the start button can start the motor. The same condition exists if the ground fault is in the wiring rather than in the control device itself. This hazardous condition can be alleviated by locating the start button in the ungrounded side of the control circuit, as shown in the exhibit below. Combinations of ground faults in motor and motor control circuits can also result in inadvertent motor starting. If the circuit is ungrounded, the first fault could go undetected. One solution is to use double-pole control devices with one pole in each of the two control lines. 430.75 Disconnection. (A) General. Motor control circuits shall be arranged so that they will be disconnected from all sources of supply when the disconnecting means is in the open position. The disconnecting means shall be permitted to consist of two or more separate devices, one of which disconnects the motor and the motor controller from the source(s) of power supply for the motor, and the other(s), the motor control circuit(s) from its power supply. Where separate devices are used, they shall be located immediately adjacent to each other. Exception No. 1: Where more than 12 motor control circuit conductors are required to be disconnected, the disconnecting means shall be permitted to be located other than immediately adjacent to each other where all of the following conditions are met: (1) Access to energized parts is limited to qualified persons in accordance with Part XII of this article. (2) A warning sign is permanently located on the outside of each equipment enclosure door or cover permitting access to the live parts in the motor control circuit(s), warning that motor control circuit disconnecting means are remotely located and specifying the location and identification of each disconnect. Where energized parts are not in an equipment enclosure as permitted by 430.232 and 430.233, an additional warning sign(s) shall be located where visible to persons who may be working in the area of the energized parts. Exception No. 2: The motor control circuit disconnecting means shall be permitted to be remote from the motor controller power supply disconnecting means where the opening of one or more motor control circuit disconnecting means is capable of resulting in potentially unsafe conditions for personnel or property and the conditions of items (1) and (2) of Exception No. 1 are met. (B) Control Transformer in Motor Controller Enclosure. Where a transformer or other device is used to obtain a reduced voltage for the motor control circuit and is located in the motor controller enclosure, such transformer or other device shall be connected to the load side of the disconnecting means for the motor control circuit. Part VII. Motor Controllers 430.81 General. Part VII is intended to require suitable motor controllers for all motors. Stationary Motor of 1⁄8 Horsepower or Less. For a stationary motor rated at 1⁄8 hp or less that is normally left running and is constructed so that it cannot be damaged by overload or failure to start, such as clock motors and the like, the branch-circuit disconnecting means shall be permitted to serve as the motor controller. Portable Motor of 1⁄3 Horsepower or Less. For a portable motor rated at 1⁄3 hp or less, the motor controller shall be permitted to be an attachment plug and receptacle or cord connector. 430.82 Motor Controller Design. (A) Starting and Stopping. Each motor controller shall be capable of starting and stopping the motor it controls and shall be capable of interrupting the locked-rotor current of the motor. Autotransformer. An autotransformer starter shall provide an “off” position, a running position, and at least one starting position. It shall be designed so that it cannot rest in the starting position or in any position that will render the overload device in the circuit inoperative. Rheostats. Rheostats shall be in compliance with the following: Motor-starting rheostats shall be designed so that the contact arm cannot be left on intermediate segments. The point or plate on which the arm rests when in the starting position shall have no electrical connection with the resistor. Motor-starting rheostats for dc motors operated from a constant voltage supply shall be equipped with automatic devices that will interrupt the supply before the speed of the motor has fallen to less than one-third its normal rate. 430.83 Ratings. The motor controller shall have a rating in accordance with 430.83(A), unless otherwise permitted in 430.83(B) or (C), or in accordance with (D), under the conditions specified. General. Horsepower Ratings. Motor controllers, other than inverse time circuit breakers and molded case switches, shall have horsepower ratings at the application voltage not lower than the horsepower rating of the motor. Circuit Breaker. A branch-circuit inverse time circuit breaker rated in amperes shall be permitted as a motor controller for all motors. Where this circuit breaker is also used for overload protection, it shall conform to the appropriate provisions of this article governing overload protection. Molded Case Switch. A molded case switch rated in amperes shall be permitted as a motor controller for all motors. ENHANCED CONTENT Collapse A molded case switch has the same frame appearance as a molded case circuit breaker and is designed to fit in circuit-breaker enclosures. However, the device is marked with only a short-circuit current rating, which indicates that the switch does not provide overcurrent protection. Fused molded case switches that do provide overcurrent protection are marked with a short-circuit current interrupting rating. Both fused and unfused molded case switches can be used in motor circuits. Molded case switches are permitted as motor disconnecting means per 430.109. In general, molded case switches are rated only in amperes and, where used in a motor circuit, must be sized at 115 percent of the motor full-load current rating. Disconnecting means assemblies are available that employ molded case switches marked with horsepower ratings that can be used, instead of the ampere rating of the molded case switch. Small Motors. Devices in accordance with 430.81(A) and (B) shall be permitted as a motor controller. Stationary Motors of 2 Horsepower or Less. For stationary motors rated at 2 hp or less and 300 volts or less, the motor controller shall be permitted to be either of the following: A general-use switch having an ampere rating not less than twice the full-load current rating of the motor On ac circuits, a general-use snap switch suitable only for use on ac (not general-use ac–dc snap switches) where the motor full-load current rating is not more than 80 percent of the ampere rating of the switch Torque Motors. For torque motors, the motor controller shall have a continuous-duty, full-load current rating not less than the nameplate current rating of the motor. For a motor controller rated in horsepower but not marked with the foregoing current rating, the equivalent current rating shall be determined from the horsepower rating by using Table 430.247, Table 430.248, Table 430.249, or Table 430.250. Voltage Rating. A motor controller with a straight voltage rating, for example, 240 volts or 480 volts, shall be permitted to be applied in a circuit in which the nominal voltage between any two conductors does not exceed the motor controller’s voltage rating. A motor controller with a slash rating, for example, 120/240 volts or 480Y/277 volts, shall only be applied in a solidly grounded circuit in which the nominal voltage to ground from any conductor does not exceed the lower of the two values of the motor controller’s voltage rating and the nominal voltage between any two conductors does not exceed the higher value of the motor controller’s voltage rating. Short-Circuit Current Rating. A motor controller shall not be installed where the available fault current exceeds the motor controller’s short-circuit current rating. Informational Note: The short-circuit current rating might be marked on the device or might be a rating for a tested combination specified in the motor controller’s technical manual or instruction sheet. 430.84 Need Not Open All Conductors. The motor controller shall not be required to open all conductors to the motor. Exception: Where the motor controller serves also as a disconnecting means, it shall open all ungrounded conductors to the motor in accordance with 430.111. ENHANCED CONTENT Collapse A controller that does not serve as a disconnecting means must open only as many motor circuit conductors as are necessary to stop the motor — that is, one conductor for a dc or single-phase motor circuit, two conductors for a 3-phase motor circuit, and three conductors for a 2-phase motor circuit. 430.85 In Grounded Conductors. One pole of the motor controller shall be permitted to be placed in a permanently grounded conductor if the motor controller is designed so that the pole in the grounded conductor cannot be opened without simultaneously opening all conductors of the circuit. ENHANCED CONTENT Collapse Generally, one conductor of a 120-volt circuit is grounded, and a single-pole device must be connected in the ungrounded conductor to serve as a controller. A 2-pole controller is permitted for such a circuit, where both conductors (grounded and ungrounded) are opened simultaneously. The same requirement can be applied to other circuits, such as 240-volt, 3-wire circuits with one conductor grounded. 430.87 Number of Motors Served by Each Motor Controller. Each motor shall be provided with an individual motor controller. Exception No. 1: For motors rated 1000 volts or less, a single motor controller rated at not less than the equivalent horsepower, as determined in accordance with 430.110(C)(1), of all the motors in the group shall be permitted to serve the group under any of the following conditions: (1) Where a number of motors drive several parts of a single machine or piece of apparatus, such as metal and woodworking machines, cranes, hoists, and similar apparatus (2) Where a group of motors is under the protection of one overcurrent device in accordance with 430.53(A) (3) Where a group of motors is located in a single room within sight from the motor controller location Exception No. 2: A branch-circuit disconnecting means serving as the motor controller in accordance with 430.81(A) shall be permitted to serve more than one motor. 430.88 Adjustable-Speed Motors. Adjustable-speed motors that are controlled by means of field regulation shall be equip⁠ped and connected so that they cannot be started under a weakened field. Exception: Starting under a weakened field shall be permitted where the motor is designed for such starting. ENHANCED CONTENT Collapse The torque and speed of a dc motor depend on the amount of current passing through the armature. This current is a function of the shunt field strength and the RPM of the armature. A reduction of the shunt field magnetic flux causes a reduction of the counterelectromotive force in the armature, resulting in an increase in armature current, thereby increasing torque, which increases speed. 430.89 Speed Limitation. Machines of the following types shall be provided with speed-limiting devices or other speed-limiting means: (1) Separately excited dc motors Series motors Motor-generators and converters that can be driven at excessive speed from the dc end, as by a reversal of current or decrease in load Exception: Separate speed-limiting devices or means shall not be required under either of the following conditions: (1) Where the inherent characteristics of the machines, the system, or the load and the mechanical connection thereto are such as to safely limit the speed (2) Where the machine is always under the manual control of a qualified operator ENHANCED CONTENT Collapse Use of dc motors is common where speed control is essential, such as electric railways and elevators, where a smooth start, controlled acceleration, and a smooth stop are necessary. If the load is removed from a series motor when it is running, the speed of the motor will increase until it is dangerously high. To produce the necessary counterelectromotive force with a weakened field, the armature must turn correspondingly faster. Series motors are commonly used as gear-drive traction motors of electric locomotives and, thus, are continuously loaded. Unless the exception applies, the motors, motor (compound-wound dc) generators, and (synchronous) converters must be provided with speed-limiting devices, such as a centrifugal device on the shaft of the machine or a remotely located overspeed device. This device can be set to operate a set of contacts at a predetermined speed and thereby trip a circuit breaker and de-energize the machine. 430.90 Combination Fuseholder and Switch as Motor Controller. The rating of a combination fuseholder and switch used as a motor controller shall be such that the fuseholder will accommodate the size of the fuse specified in Part III of this article for motor overload protection. Exception: Where fuses having time delay appropriate for the starting characteristics of the motor are used, fuseholders of smaller size than specified in Part III of this article shall be permitted. Part VIII. Motor Control Centers 430.92 General. Part VIII covers motor control centers instal⁠led for the control of motors, lighting, and power circuits. ENHANCED CONTENT Collapse Motor control centers are made up of several motor starters, controls, and disconnect switches. Motor control centers are allowed to be used as service equipment if provided with a single main disconnecting means. A second service disconnecting means, however, is permitted in the motor control center if it is provided to serve other loads. In addition to Part VIII, installation requirements, including access and working space clearances, for motor control centers are covered in Section 110.26. The requirements of 110.26(E) specify dedicated space for a motor control center and physical protection from mechanical systems that might leak or otherwise adversely affect a motor control center. 430.94 Overcurrent Protection. Motor control centers shall be provided with overcurrent protection in accordance with Parts I, II, and VIII of Article 240. The ampere rating or setting of the overcurrent protective device shall not exceed the rating of the common power bus. This protection shall be provided by (1) an overcurrent protective device located ahead of the motor control center or (2) a main overcurrent protective device located within the motor control center. 430.95 Service Equipment. Where used as service equipment, each motor control center shall be provided with a single main disconnecting means to disconnect all ungrounded service conductors. Exception No. 1: A second service disconnect shall be permitted to supply additional equipment. Where a grounded conductor is provided, the motor control center shall be provided with a main bonding jumper, sized in accordance with 250.28(D), within one of the sections for connecting the grounded conductor, on its supply side, to the motor control center equipment ground bus. Exception No. 2: High-impedance grounded neutral systems shall be permitted to be connected as provided in 250.36. 430.96 Grounding. Multisection motor control centers shall be connected together with an equipment grounding conductor or an equivalent equipment grounding bus sized in accordance with Table 250.122. Equipment grounding conductors shall be connected to this equipment grounding bus or to a grounding termination point provided in a single-section motor control center. 430.97 Busbars and Conductors. (A) Support and Arrangement. Busbars shall be protected from physical damage and be held firmly in place. Other than for required interconnections and control wiring, only those conductors that are intended for termination in a vertical section shall be located in that section. Exception: Conductors shall be permitted to travel horizontally through vertical sections where such conductors are isolated from the busbars by a barrier. (B) Phase Arrangement. The phase arrangement on 3-phase horizontal common power and vertical buses shall be A, B, C from front to back, top to bottom, or left to right, as viewed from the front of the motor control center. The B phase shall be that phase having the higher voltage to ground on 3-phase, 4-wire, delta-connected systems. Other busbar arrangements shall be permitted for additions to existing installations and shall be marked. Exception: Rear-mounted units connected to a vertical bus that is common to front-mounted units shall be permitted to have a C, B, A phase arrangement where properly identified. (C) Minimum Wire-Bending Space. The minimum wire-bending space at the motor control center terminals and minimum gutter space shall be in accordance with 312.6. Spacings. Spacings between motor control center bus terminals and other bare metal parts shall not be less than specified in Table 430.97(D). Barriers. Barriers shall be placed in all service-entrance motor control centers to isolate service busbars and terminals from the remainder of the motor control center. Table 430.97(D) Minimum Spacing Between Bare Metal Parts Nominal Voltage Opposite Polarity Where Mounted on the Same Surface Opposite Polarity Where Held Free in Air Live Parts to Ground mm in. mm in. mm in. Not over 125 volts, nominal 19.1 3⁄ 4 12.7 1⁄ 2 12.7 1⁄ 2 Not over 250 volts, nominal 31.8 11⁄4 19.1 3⁄ 4 12.7 1⁄ 2 Not over 600 volts, nominal 50.8 2 25.4 1 25.4 1 430.98 Marking. (A) Motor Control Centers. Motor control centers shall be marked according to 110.21, and the marking shall be plainly visible after installation. Marking shall also include common power bus current rating and motor control center short-circuit current rating. Motor Control Units. Motor control units in a motor control center shall comply with 430.8. 430.99 Available Fault Current. The available fault current at the motor control center and the date the available fault current calculation was performed shall be documented and made available to those authorized to inspect, install, or maintain the installation. ENHANCE