Resolución 2535: adopta el Código Eléctrico Nacional, versión 1993. (Sustituye el Anejo A del Reglamento 4435)

Exception No. 1: Control circuit transformers rated less than 50 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. Exception No. 2: 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. Exception No. 3: Where the transformer supplies a Class 1 powerlimited circuit [see Section 725-11(a)], Class 2, or Class 3 remote-control circuit conforming with the requirements of Article 725. See Article 725, Part C. Exception No. 4: Where protection is provided by other approved means. 70-412 NATIONAL ELECTRICAL CODE Exception No. 5: 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. 430-73. Mechanical Protection of Conductor. 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 suitably protected from physical damage. Where one side of the motor control circuit is grounded, the motor control circuit shall be so arranged that an accidental ground in the remotecontrol devices will (1) not start the motor, and (2) not bypass manually operated shutdown devices or automatic safety shutdown devices. 430-74. Disconnection. (a) General. Motor control circuits shall be so arranged 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 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 one to each other. Exception No. 1: Where more than twelve motor control circuit conductors are required to be disconnected, the disconnecting means shall be permitted to be located other than immediately adjacent one to each other where all of the following conditions are complied with: a. Access to energized parts is limited to qualified persons in accordance with Part K of this article. b. 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 Sections 430-132 and 430-133, 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: Where the opening of one or more motor control circuit disconnect means may result in potentially unsafe conditions for personnel or property and the conditions of items a and b of Exception No. 1 above are complied with. (b) Control Transformer in 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 controller enclosure, such transformer or other device shall be connected to the load side of the disconnecting means for the motor control circuit. ARTICLE 430 - MOTOR CIRCUITS, CONTROLLERS 70-413 G. Motor Controllers 430-81. General. Part G is intended to require suitable controllers for all motors. (a) Definition. For definition of "Controller," see Article 100. For the purpose of this article, a controller is any switch or device normally used to start and stop a motor by making and breaking the motor circuit current. (b) Stationary Motor of 1/8 Horsepower or Less. For a stationary motor rated at ¹/₈ horsepower or less that is normally left running and is so constructed that it cannot be damaged by overload or failure to start, such as clock motors and the like, the branch-circuit protective device shall be permitted to serve as the controller. (c) Portable Motor of ¼ Horsepower or Less. For a portable motor rated at ½ horsepower or less, the controller shall be permitted to be an attachment plug and receptacle. 430-82. Controller Design. (a) Starting and Stopping. Each 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. (b) Autotransformer. An autotransformer starter shall provide an "off" position, a running position, and at least one starting position. It shall be so designed that it cannot rest in the starting position or in any position that will render the overload device in the circuit inoperative. (c) Rheostats. Rheostats shall be in compliance with the following: (1) Motor-starting rheostats shall be so designed 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. (2) Motor-starting rheostats for direct-current 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. (a) Horsepower Rating at the Application Voltage. The controller shall have a horsepower rating at the application voltage not lower than the horsepower rating of the motor. Exception No. 1: For a stationary motor rated at 2 horsepower or less, and 300 volts or less, the controller shall be permitted to be a general-use switch having an ampere rating not less than twice the full-load current rating of the motor. On ac circuits, general-use snap switches suitable only for use on ac (not general-use ac-dc snap switches) shall be permitted to control a motor rated at 2 horsepower or less, and 300 volts or less, having a 70-414 NATIONAL ELECTRICAL CODE full-load current rating not more than 80 percent of the ampere rating of the switch. Exception No. 2: A branch-circuit inverse time circuit breaker rated in amperes only shall be permitted as a controller. Where this circuit breaker is also used for overload protection, it shall conform to the appropriate provisions of this article governing overload protection. Exception No. 3: The motor controller for a torque motor 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 430-147, 430-148, 430-149, or 430-150. (b) Voltage Rating. A controller with a straight voltage rating, e.g., 240V or 480V, shall be permitted to be applied in a circuit in which the nominal voltage between any two conductors does not exceed the controller's voltage rating. A controller with a slash rating, e.g., 120/240V or 480/277V, shall only be applied in a circuit in which the nominal voltage to ground from any conductor does not exceed the lower of the two values of the controller's voltage rating and the nominal voltage between any two conductors does not exceed the higher value of the controller's voltage rating. 430-84. Need Not Open All Conductors. The controller shall not be required to open all conductors to the motor. Exception: Where the controller serves also as a disconnecting means, it shall open all ungrounded conductors to the motor as provided in Section 430-111. 430-85. In Grounded Conductors. One pole of the controller shall be permitted to be placed in a permanently grounded conductor, provided the controller is so designed that the pole in the grounded conductor cannot be opened without simultaneously opening all conductors of the circuit. 430-87. Number of Motors Served by Each Controller. Each motor shall be provided with an individual controller. Exception: For motors rated 600 volts or less, a single controller rated at not less than the sum of the horsepower ratings of all of the motors of the group shall be permitted to serve the group of motors under any one of the following conditions: a. 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. b. Where a group of motors is under the protection of one overcurrent device as permitted in Section 430-53(a). C. Where a group of motors is located in a single room within sight from the controller location. ARTICLE 430 - MOTOR CIRCUITS, CONTROLLERS 70-415 430-88. Adjustable-Speed Motors. Adjustable-speed motors that are controlled by means of field regulation shall be so equipped and connected that they cannot be started under weakened field. Exception: Where the motor is designed for such starting. 430-89. Speed Limitation. Machines of the following types shall be provided with speed limiting devices or other speed limiting means: (a) Separately Excited DC Motors. Separately excited direct-current motors. (b) Series Motors. Series motors. (c) Motor-Generators and Converters. Motor-generators and converters that can be driven at excessive speed from the direct-current end, as by a reversal of current or decrease in load. Exception No. 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. Exception No. 2: Where the machine is always under the manual control of a qualified operator. 430-90. Combination Fuseholder and Switch as 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 C 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 C of this article shall be permitted. 430-91. Motor Controller Enclosure Types. Table 430-91 provides the basis for selecting enclosures for use in specific nonhazardous locations. The enclosures are not intended to protect against conditions such as condensation, icing, corrosion, or contamination that may occur within the enclosure or enter via the conduit or unsealed openings. These internal conditions require special consideration by the installer and user. H. Motor Control Centers 430-92. General. Part H covers motor control centers installed for the control of motors, lighting, and power circuits. A motor control center is an assembly of one or more enclosed sections having a common power bus and principally containing motor control units. 430-94. Overcurrent Protection. Motor control centers shall be provided with overcurrent protection in accordance with Article 240 based on the rating of the common power bus. This protection shall be provided by either (1) an upstream overcurrent-protective device or (2) a main overcurrent-protective device located within the motor control center. 70-416 NATIONAL ELECTRICAL CODE Table 430-91. Motor Controller Enclosure Selection Table For Outdoor Use Provides a Degree of Protection Enclosure Type Number t Against the Following Environmental Conditions 3 3 R 3 S 4 4X 6 6P Incidental contact with the enclosed equipment X X X X X X X Rain, snow, and sleet X X X X X X X Sleet* - X Windblown dust X - X X X X X Hosedown - X X X X Corrosive agents - - - X - X Occasional temporary submersion - - - - - X X Occasional prolonged submersion - - - - - - X *Mechanism shall be operable when ice covered. For Indoor Use Provides a Degree of Protection Enclosure Type Number t Against the Following Environmental Conditions 1 2 4 4 X 5 6 6P 12 12K 13 Incidental contact with the enclosed equipment X X X X X X X X X X Falling dirt X X X X X X X X X X Falling liquids and light splashing - X X X X X X X X X Circulating dust, lint, fibers, and flyings - - X X - X X X X X Settling airborne dust, lint, fibers, and flyings - - X X X X X X X X Hosedown and splasing water - - X X - X X - - Oil and coolant seepage - - - X X X Oil or coolant spraying and splashing - - - X Corrosive agents - - X - X --- - Occasional temporary submersion | - X X - | - Occasional prolonged submersion - - X tEnclosure type number shall be marked on the motor controller enclosure. 430-95. Service-Entrance 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: A second service disconnect shall be permitted to supply additional equipment. Where a grounded (neutral) conductor is provided, the motor control center shall be provided with a main bonding jumper, sized in accordance with Section 250-79(d), within one of the sections for connecting the grounded (neutral) conductor, on its supply side, to the motor control center equipment ground bus. ARTICLE 430 - MOTOR CIRCUITS, CONTROLLERS 70-417 430-96. Grounding. Multisection motor control centers shall be bonded together with an equipment grounding conductor or an equivalent grounding bus sized in accordance with Table 250-95. Equipment grounding conductors shall terminate on this 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 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. 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 as required in Article 373. (d) Spacings. Spacings between motor control center bus terminals and other bare metal parts shall not be less than specified in Table 430-97. Table 430-97. Minimum Spacing Between Bare Metal Parts Opposite Polarity Opposite Polarity Where Mounted on Where Held Live Parts the Same Surface Free in Air to Ground Not over 125 volts, nominal 3/4 inch 1/2 inch ½ inch Not over 250 volts, nominal 1½ inch 3/4 inch ½ inch Not over 600 volts, nominal 2 inches 1 inch 1 inch For SI units: one inch = 25.4 millimeters. (e) 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. 430-98. Marking. (a) Motor Control Centers. Motor control centers shall be marked according to Section 110-21, and such marking shall be plainly visible after installation. Marking shall also include common power bus current rating and motor control center short-circuit rating. 70-418 NATIONAL ELECTRICAL CODE (b) Motor Control Units. Motor control units in a motor control center shall comply with Section 430-8. I. Disconnecting Means 430-101. General. Part I is intended to require disconnecting means capable of disconnecting motors and controllers from the circuit. (FPN No. 1): See Diagram 430-1. (FPN No. 2): See Section 110-22 for identification of disconnecting means. 430-102. Location. (a) Controller. A disconnecting means shall be located in sight from the controller location and shall disconnect the controller. Exception No. 1: For motor circuits over 600 volts, nominal, a controller disconnecting means capable of being locked in the open position shall be permitted to be out of sight of the controller, provided the controller is marked with a warning label giving the location of the disconnecting means. Exception No. 2: A single disconnecting means shall be permitted to be located adjacent to a group of coordinated controllers mounted adjacent one to each other on a multimotor continuous process machine. (b) Motor. A disconnecting means shall be located in sight from the motor location and the driven machinery location. Exception: Where the disconnecting means provided in accordance with Section 430-102(a) is capable of being locked in the open position. 430-103. Operation. The disconnecting means shall open all ungrounded supply conductors and shall be so designed that no pole can be operated independently. The disconnecting means shall be permitted in the same enclosure with the controller. (FPN): See Section 430-113 for equipment receiving energy from more than one source. 430-104. To Be Indicating. The disconnecting means shall plainly indicate whether it is in the open ("off") or closed ("on") position. 430-105. Grounded Conductors. One pole of the disconnecting means shall be permitted to disconnect a permanently grounded conductor, provided the disconnecting means is so designed that the pole in the grounded conductor cannot be opened without simultaneously disconnecting all conductors of the circuit. 430-106. Service Switch as Disconnecting Means. Where an installation consists of a single motor, the service switch shall be permitted to serve as the disconnecting means if it complies with this article and is within sight from the controller location. 430-107. Readily Accessible. One of the disconnecting means shall be readily accessible. ARTICLE 430 - MOTOR CIRCUITS, CONTROLLERS 70-419 430-108. Every Switch. Every disconnecting means in the motor branch circuit between the point of attachment to the feeder and the point of connection to the motor shall comply with the requirements of Sections 430-109 and 430-110. 430-109. Type. The disconnecting means shall be one of the following types: a motor-circuit switch rated in horsepower, a circuit breaker, or a molded-case switch, and shall be a listed device. Exception No. 1: For stationary motors of 1/8 horsepower or less, the branch-circuit overcurrent device shall be permitted to serve as the disconnecting means. Exception No. 2: For stationary motors rated at 2 horsepower or less and 300 volts or less, the disconnecting means shall be permitted to be a general-use switch having an ampere rating not less than twice the fullload current rating of the motor. On ac circuits, general-use snap switches suitable only for use on ac (not general-use ac-dc snap switches) shall be permitted to disconnect a motor rated 2 horsepower or less and 300 volts or less having a full-load current rating not more than 80 percent of the ampere rating of the switch. Exception No. 3: For motors of over 2 horsepower to and including 100 horsepower, the separate disconnecting means required for a motor with an autotransformer-type controller shall be permitted to be a general-use switch where all of the following provisions are met: a. The motor drives a generator that is provided with overload protection. b. The controller (1) is capable of interrupting the locked-rotor current of the motor; (2) is provided with a no-voltage release; and (3) is provided with running overload protection not exceeding 125 percent of the motor full-load current rating. c. Separate fuses or an inverse time circuit breaker rated or set at not more than 150 percent of the motor full-load current are provided in the motor branch circuit. Exception No. 4: For stationary motors rated at more than 40 horsepower direct current or 100 horsepower alternating current, the disconnecting means shall be permitted to be a general-use or isolating switch where plainly marked "Do not operate under load." Exception No. 5: For a cord- and plug-connected motor, a horsepowerrated attachment plug and receptacle having ratings no less than the motor ratings shall be permitted to serve as the disconnecting means. A horsepower-rated attachment plug and receptacle shall not be required for a cord- and plug-connected appliance in accordance with Section 422-22, a room air conditioner in accordance with Section 440-63, or a portable motor rated 1/3 horsepower or less. Exception No. 6: For torque motors, the disconnecting means shall be permitted to be a general-use switch. Exception No. 7: An instantaneous trip circuit breaker that is part of a listed combination motor controller shall be permitted to serve as a disconnecting means. 70-420 NATIONAL ELECTRICAL CODE 430-110. Ampere Rating and Interrupting Capacity. (a) General. The disconnecting means for motor circuits rated 600 volts, nominal, or less, shall have an ampere rating of at least 115 percent of the full-load current rating of the motor. (b) For Torque Motors. Disconnecting means for a torque motor shall have an ampere rating of at least 115 percent of the motor nameplate current. (c) For Combination Loads. Where two or more motors are used together or where one or more motors are used in combination with other loads, such as resistance heaters, and where the combined load may be simultaneous on a single disconnecting means, the ampere and horsepower ratings of the combined load shall be determined as follows: (1) The rating of the disconnecting means shall be determined from the summation of all currents, including resistance loads, at the full-load condition and also at the locked-rotor condition. The combined full-load current and the combined locked-rotor current so obtained shall be considered as a single motor for the purpose of this requirement as follows: The full-load current equivalent to the horsepower rating of each motor shall be selected from Table 430-148, 430-149, or 430-150. These full-load currents shall be added to the rating in amperes of other loads to obtain an equivalent full-load current for the combined load. The locked-rotor current equivalent to the horsepower rating of each motor shall be selected from Table 430-151. The locked-rotor currents shall be added to the rating in amperes of other loads to obtain an equivalent locked-rotor current for the combined load. Where two or more motors or other loads cannot be started simultaneously, appropriate combinations of locked-rotor and full-load current shall be permitted to be used to determine the equivalent locked-rotor current for the simultaneous combined loads. Exception: Where part of the concurrent load is resistance load, and where the disconnecting means is a switch rated in horsepower and amperes, the switch used shall be permitted to have a horsepower rating not less than the combined load of the motor(s), if the ampere rating of the switch is not less than the locked-rotor current of the motor(s) plus the resistance load. (2) The ampere rating of the disconnecting means shall not be less than 115 percent of the summation of all currents at the full-load condition determined in accordance with (c)(1) above. (3) For small motors not covered by Tables 430-147, 430-148, 430-149, or 430-150, the locked-rotor current shall be assumed to be six times the full-load current. 430-111. Switch or Circuit Breaker as Both Controller and Disconnecting Means. A switch or circuit breaker complying with Section 430-83 shall be permitted to serve as both controller and disconnecting means if it opens all ungrounded conductors to the motor, if it is protected by an overcurrent device (which shall be permitted to be the branch-circuit fuses) that opens all ungrounded conductors to the switch or circuit breaker, and if it is of one of the types specified in (a), (b), or (c) below: ARTICLE 430 - MOTOR CIRCUITS, CONTROLLERS 70-421 (a) Air-Break Switch. An air-break switch, operable directly by applying the hand to a lever or handle. (b) Inverse Time Circuit Breaker. An inverse time circuit breaker operable directly by applying the hand to a lever or handle. (c) Oil Switch. An oil switch used on a circuit whose rating does not exceed 600 volts or 100 amperes, or by special permission on a circuit exceeding this capacity where under expert supervision. The oil switch or circuit breaker specified above shall be permitted to be both power and manually operable. The overcurrent device protecting the controller shall be permitted to be part of the controller assembly or shall be permitted to be separate. An autotransformer-type controller shall be provided with a separate disconnecting means. 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 a, b, and c below. The single disconnecting means shall be rated in accordance with Section 430-110(c): a. 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. b. Where a group of motors is under the protection of one set of branch-circuit protective devices as permitted by Section 430-53(a). c. Where a group of motors is in a single room within sight from the location of the disconnecting means. 430-113. Energy from More than One Source. Motor and motor-operated equipment receiving electrical energy from more than one source shall be provided with disconnecting means from each source of electrical energy immediately adjacent to the equipment served. Each source shall be permitted to have a separate disconnecting means. Exception No. 1: Where a motor receives electrical 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, provided the controller disconnecting means is capable of being locked in the open position. Exception No. 2: A separate disconnecting means shall not be required for a Class 2 remote-control circuit conforming with Article 725, rated not more than 30 volts, and that is isolated and ungrounded. J. Over 600 Volts, Nominal 430-121. General. Part J recognizes the additional hazard due to the use of higher voltages. It adds to or amends the other provisions of this article. Other requirements for circuits and equipment operating at over 600 volts, nominal, are in Article 710. 70-422 NATIONAL ELECTRICAL CODE 430-122. Marking on Controllers. In addition to the marking required by