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D CONTENT Collapse A motor control center is required to be marked with its short-circuit current rating per 430.98. The requirement in 430.99 requires the motor control center to be marked with the available short-circuit current. This provides a means to easily compare the equipm...

D CONTENT Collapse A motor control center is required to be marked with its short-circuit current rating per 430.98. The requirement in 430.99 requires the motor control center to be marked with the available short-circuit current. This provides a means to easily compare the equipment rating with the available fault current and to confirm compliance with 110.10. Part IX. Disconnecting Means 430.101 General. Part IX is intended to require disconnecting means capable of disconnecting motors and motor controllers from the circuit. 430.102 Location. Motor Controller. An individual disconnecting means shall be provided for each motor controller and shall disconnect the motor controller. The disconnecting means shall be located in sight from the motor controller location. Exception No. 1: For motor circuits over 1000 volts, nominal, a motor controller disconnecting means lockable in accordance with 110.25 shall be permitted to be out of sight of the motor controller if the motor controller is marked with a label giving the location of the disconnecting means. Exception No. 2: A single disconnecting means shall be permitted for a group of coordinated motor controllers that drive several parts of a single machine or piece of apparatus. The disconnecting means shall be located in sight from the motor controllers, and both the disconnecting means and the motor controllers shall be located in sight from the machine or apparatus. Exception No. 3: The disconnecting means shall not be required to be in sight from valve actuator motor (VAM) assemblies containing the motor controller where such a location introduces additional or increased hazards to persons or property and the following conditions are met: (1) The valve actuator motor assembly is marked with a label giving the location of the disconnecting means. (2) The disconnecting means is lockable in accordance with 110.25. (B) Motor. A disconnecting means shall be provided for a motor in accordance with 430.102(B)(1) or (B)(2). Separate Motor Disconnect. A disconnecting means for the motor shall be located in sight from the motor location and the driven machinery location. Motor Controller Disconnect. The motor controller disconnecting means required in accordance with 430.102(A) shall be permitted to serve as the disconnecting means for the motor if it is in sight from the motor location and the driven machinery location. Exception to (1) and (2): The disconnecting means for the motor shall not be required under either of the following conditions if the motor controller disconnecting means required in 430.102(A) is lockable in accordance with 110.25: (1) Where such a location of the disconnecting means for the motor is impracticable or introduces additional or increased hazards to persons or property Informational Note No. 1: Some examples of increased or additional hazards include, but are not limited to, motors rated in excess of 100 hp, multimotor equipment, submersible motors, motors associated with adjustable-speed drives, and motors located in hazardous (classified) locations. (2) In industrial installations, with written safety procedures, where conditions of maintenance and supervision ensure that only qualified persons service the equipment Informational Note No. 2: See NFPA 70E -2021, Standard for Electrical Safety in the Workplace, for information on lockout/tagout procedures. ENHANCED CONTENT Collapse The main rules of 430.102(A) and (B) require that the disconnecting means be in sight of the controller, the motor location, and the driven machinery location. The exceptions to these rules permit the disconnecting means to be out of sight under certain conditions, which include that it be capable of being locked in the open position. A single disconnecting means may be located adjacent to a group of coordinated controllers, as illustrated in the exhibit below, where the controllers are mounted on a multimotor continuous process machine. According to 430.102(B)(2), Exception, the disconnecting means is permitted to be out of sight of the motor — as illustrated below — if the controller disconnecting means is individually capable of being locked in the open position and the condition of either (1) or (2) is met. Locating disconnect switches or panelboards within locked rooms or circuit breakers behind the locked door of a panelboard does not meet the requirements of 430.102. If locating the disconnecting means close to the motor location and driven machinery is impracticable due to the type of machinery, the type of facility, lack of space for locating large equipment such as disconnecting means rated over 1000 volts, or any increased hazard to persons or property, the disconnecting means is permitted to be located remotely. Industrial facilities that comply with OSHA 29 CFR 1910.147, “The Control of Hazardous Energy (Lockout/Tagout),” are permitted to have the disconnecting means located remotely. Section 110.2 of NFPA 70E, Standard for Electrical Safety in the Workplace, requires in part that all “electrical conductors and circuit parts shall not be considered to be in an electrically safe work condition until all of the requirements of Article 120 have been met.” The work process specified in Article 120 of NFPA 70E includes removing the sources of energy, locking, and tagging out the disconnecting means, and verifying the absence of voltage using an approved voltage tester. Further, 120.1(A)(3) of NFPA 70E states that lockout/tagout requirements shall “apply to fixed, permanently installed equipment, temporarily installed equipment and portable equipment.” The principles and procedures in NFPA 70E establish strict work rules requiring the locking off (out) and tagging out of disconnect switches. 430.103 Operation. The disconnecting means shall open all ungrounded supply conductors and shall be designed so that no pole can be operated independently. The disconnecting means shall be permitted in the same enclosure with the motor controller. The disconnecting means shall be designed so that it cannot be closed automatically. Informational Note: See 430.113 for equipment receiving energy from more than one source. ENHANCED CONTENT Collapse A switch, circuit breaker, or other device serves as a disconnecting means for both the controller and the motor, thereby providing safety during maintenance and inspection shutdown periods. The disconnecting means also disconnects the controller; therefore, it cannot be a part of the controller. However, separate disconnects and controllers may be mounted on the same panel or contained in the same enclosure, such as combination fused-switch, magnetic-starter units. Depending on the size of the motor and other conditions, the type of disconnecting means required may be a motor circuit switch, a circuit breaker, a general-use switch, an isolating switch, an attachment plug and receptacle, or a branch-circuit short-circuit and ground-fault protective device, as specified in 430.109. If a motor stalls or is under heavy overload and the motor controller fails to properly open the circuit, the disconnecting means, which must be rated to interrupt locked-rotor current, can be used to open the circuit. In accordance with 430.109(E), for motors larger than 100 horsepower ac or 40 horsepower dc, the disconnecting means is permitted to be a general-use or an isolating switch that is plainly marked “Do not operate under load.” 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 designed so that the pole in the grounded conductor cannot be opened without simultaneously disconnecting all conductors of the circuit. 430.107 Readily Accessible. At least one of the disconnecting means shall be readily accessible. 430.108 Every Disconnecting Means. Every disconnecting means in the motor circuit between the point of attachment to the feeder or branch circuit and the point of connection to the motor shall comply with the requirements of 430.109 and 430.110. 430.109 Type. The disconnecting means shall be a type in accordance with 430.109(A), unless otherwise permitted in 430.109(B) through (G), under the conditions specified. General. Motor-Circuit Switch. A listed motor-circuit switch rated in horsepower. Molded Case Circuit Breaker. A listed molded case circuit breaker. Molded Case Switch. A listed molded case switch. Instantaneous-Trip Circuit Breaker. An instantaneous-trip circuit breaker that is part of a listed combination motor controller. Self-Protected Combination Motor Controller. Listed self-protected combination motor controller. Manual Motor Controller. Listed manual motor controllers additionally marked “Suitable as Motor Disconnect” shall be permitted as a disconnecting means where installed between the final motor branch-circuit short-circuit protective device and the motor. Listed manual motor controllers additionally marked “Suitable as Motor Disconnect” shall be permitted as disconnecting means on the line side of the fuses in accordance with 430.52(C)(5). In this case, the fuses permitted in 430.52(C)(5) shall be considered supplementary fuses, and suitable branch-circuit short-circuit and ground-fault protective devices shall be installed on the line side of the manual motor controller additionally marked “Suitable as Motor Disconnect.” System Isolation Equipment. System isolation equipment shall be listed for disconnection purposes. System isolation equipment shall be installed on the load side of the overcurrent protection and its disconnecting means. The disconnecting means shall be one of the types permitted by 430.109(A)(1) through (A)(3). ENHANCED CONTENT Collapse Unlike other disconnecting means recognized by 430.109(A) where the operation of the disconnecting means directly opens the supply circuit at that specific location, system isolation equipment (SIE) employs a lockable control circuit switch(es) (lockout switch) and a verification indication at the disconnecting means location (lockout station). Also, operation of the lockout switch causes power components such as a monitored magnetic contactor to open and isolate the electrical equipment associated with the machine from its power supply circuit. The SIE is classified according to its intended application with parameters that include the load characteristics, the method used to monitor the controlled load-side power circuit, the number and maximum distance to the farthest lockout station, and the available control interface functions. In large and often complex machines, repeated operation of disconnecting means for maintenance or servicing is inherent to the process, and the risk of injury to personnel is increased due to moving parts and multiple points of entry. This risk drives development of system isolation equipment (SIE). Safety procedures for personnel servicing this equipment include detailed lockout/tagout protocols for all sources of mechanical and electrical energy. SIE helps simplify electrical lockout/tagout procedures; it can also be used to isolate energy sources such as pneumatic energy. In accordance with its definition in Article 100, system isolation equipment is “a redundantly monitored, remotely operated contactor-isolating system, packaged to provide the disconnection/isolation function.” This type of equipment is covered in NFPA 79, Electrical Standard for Industrial Machinery, as a way to disconnect and isolate separately operable parts of a large industrial machine. With its inclusion in 430.109(A)(7) as a permitted type of disconnecting means, the NEC recognizes the use of this disconnection/isolation system in applications that do not fall within the scope of the industrial machinery standard. In a typical configuration, the contactor is located within the system power and control panel and may control power to the entire machine or to portions of a large machine. The control equipment may be provided in several configuration options for distributing to lockout stations in single or multiplexed radial schemes according to the application. Once an electrically safe condition is achieved (including discharge of any residual energy), verification of such condition is provided at the remote lockout station using an indicator light. In equipment that uses lockable guarding, the same verification signal could also be used as part of the guard access system. In contrast to a simple start/stop station and control circuit operating a magnetic contactor, the control panel for this system provides a sophisticated level of monitoring upon actuation of the remote lockout switch. If any portion of the safety system cannot be verified for proper operation, the safe condition indicator light will not illuminate at the remote lockout station. As part of the standard operating procedure, the failure to receive the safe condition signal must be considered as an indication of an unsafe condition. Among the critical safety elements that are provided by the control panel for the isolation system are the diversity and redundancy that are integrated into the safe condition verification logic. Another element is the electrical isolation of the internal safety-related control circuits and the physical isolation of the equipment’s internal components, which reduces the possibility of externally induced failure modes. The control panel modules are sealed, as are the circuits between the SIE component enclosures, to discourage tampering that could compromise the safe operation of the equipment and endanger personnel. Where the system includes multiple lockout stations, the controlled equipment cannot be re-energized until all the lockout switches are returned to the “on” position. Nominal configurations of the SIE include provisions to prevent power from unexpectedly reaching the machine upon the restoration of power from the utility source. To re-energize the machine, all lockout switches must be in the closed, or on, position while at least one lockout switch must have been in the open, or off, position or placed in the open, or off, position (and then moved to the closed, or on, position after the utility power had been restored). Stationary Motors of 1⁄8 Horsepower or Less. For stationary motors of 1⁄8 hp or less, the branch-circuit overcurrent device shall be permitted to serve as the disconnecting means. Stationary Motors of 2 Horsepower or Less. For stationary motors rated at 2 hp or less and 300 volts or less, the disconnecting means shall be permitted to be one of the following devices: 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 A listed manual motor controller having a horsepower rating not less than the rating of the motor and marked “Suitable as Motor Disconnect” Autotransformer-Type Controlled Motors. For motors of over 2 hp up to and including 100 hp, the separate disconnecting means required for a motor with an autotransformer-type motor controller shall be permitted to be a general-use switch where all of the following provisions are met: The motor drives a generator that is provided with overload protection. The motor controller is capable of interrupting the locked-rotor current of the motors, is provided with a no voltage release, and is provided with running overload protection not exceeding 125 percent of the motor full-load current rating. Separate fuses or an inverse time circuit breaker rated or set at not more than 150 percent of the motor full-load current is provided in the motor branch circuit. Isolating Switches. For stationary motors rated at more than 40 hp dc or 100 hp ac, the disconnecting means shall be permitted to be a general-use or isolating switch where plainly marked “Do not operate under load.” Cord-and-Plug-Connected Motors. For a cord-and-plug-connected motor, a horsepower-rated attachment plug and receptacle, flanged surface inlet and cord connector, or attachment plug and cord connector having ratings not less than the motor ratings shall be permitted to serve as the disconnecting means. Horsepower-rated attachment plugs, flanged surface inlets, receptacles, or cord connectors shall not be required for cord-and-plug-connected appliances in accordance with 422.33, room air conditioners in accordance with 440.63, or portable motors rated 1⁄3 hp or less. ENHANCED CONTENT Collapse A motor circuit switch is a horsepower-rated switch capable of interrupting the maximum overload current of a motor (see the definition of switch, motor-circuit in Article 100). A molded case switch (nonautomatic circuit interrupter) is a circuit breaker-like device without the overcurrent element and automatic-trip mechanism. It is rated in amperes and is suitable for use as a motor-circuit disconnect based on its ampere rating, as is a circuit breaker. The disconnecting means must be listed. Where horsepower-rated fused switches are required, marking within the enclosure usually permits a dual horsepower rating. The standard horsepower rating is based on the largest non-time-delay (non-dual-element) fuse rating that can be used in the switch and that will permit the motor to start. The maximum horsepower rating is based on the largest rated time-delay (dual-element) fuse that can be used in the switch and that will permit the motor to start. Thus, where time-delay fuses are used, smaller-size switches and fuseholders can be used (see 430.57, Exception). The following exhibits illustrate various methods of providing motor disconnecting means as permitted by 430.109(B), 430.109(C), 430.109(E), and 430.109(F). Illustrated below is a branch-circuit overcurrent device serving as the disconnecting means for a stationary motor of â…› horsepower or less according to 430.109(B). Next is a general-use snap switch serving as the disconnecting means for a stationary motor rated at 2 horsepower or less and at 300 volts or less according to 430.109(C). The exhibit below shows a general-use or an isolating switch serving as the disconnecting means for a stationary motor rated at more than 40 horsepower dc or 100 horsepower ac according to 430.109(E). The final exhibit in this group illustrates an attachment plug and receptacle serving as the disconnecting means for a certain cord-and-plug-connected motor according to 430.109(F). Torque Motors. For torque motors, the disconnecting means shall be permitted to be a general-use switch. 430.110 Current Rating and Interrupting Capacity. (A) General. The disconnecting means for motor circuits rated 1000 volts, nominal, or less shall have a current rating not less than 115 percent of the full-load current rating of the motor. Exception: A listed unfused motor-circuit switch having a horsepower rating not less than the motor horsepower shall be permitted to have a current rating less than 115 percent of the full-load current rating of the motor. (B) For Torque Motors. Disconnecting means for a torque motor shall have a current rating of at least 115 percent of the motor nameplate current. 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 can be simultaneous on a single disconnecting means, the current and horsepower ratings of the combined load shall be determined in accordance with 430.110(C)(1) through (C)(3). Horsepower Rating. The rating of the disconnecting means shall be determined from the sum 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. The full-load current equivalent to the horsepower rating of each motor shall be selected from Table 430.247, Table 430.248, Table 430.249, or Table 430.250. 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 430.251(A) or Table 430.251(B). 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, the largest sum of locked-rotor currents of a motor or group of motors that can be started simultaneously and the full-load currents of other concurrent loads shall be permitted to be used to determine the equivalent locked-rotor current for the simultaneous combined loads. In cases where different current ratings are obtained when applying these tables, the largest value obtained shall be used. Exception No. 1: The locked-rotor current equivalent to the horsepower rating of each polyphase motor with design letter A shall be one of following: (1) If available, the motor’s marked value of locked-rotor amperes (2) In the absence of a marked value of locked-rotor amperes for the motor, the value calculated from Equation 430.110(C)(1)a: [430.110(C)(1)a] code book image: 5778ecd3-aa9e-11ec-a46d-e9dd887336cb where: kVA/hp = maximum range value of kilovolt-amperes per horsepower with locked rotor in Table 430.7(B) associated with the motor’s marked locked-rotor indicating code letter Informational Note: Equation 430.110(C)(1)a is obtained by solving for locked-rotor amperes in the formula for “kilovolt-amperes per horsepower with locked rotor,” as follows:[430.110(C)(1)b]code book image: 512b00be-aa9e-11ec-a46d-e9dd887336cbThe numerator of Equation 430.110(C)(1)b for kilovolt-amperes per horsepower is the apparent power input to a three-phase motor with locked rotor in units of volt-amperes. The factor of 1000 VA/kVA in the denominator converts this value to units of kilovolt-amperes and “(marked value of rated horsepower)” in the denominator converts this to kilovolt-amperes per horsepower. Note that “motor’s marked value of rated volts” is a line-to-line value and “locked-rotor amperes” is a line value as opposed to a phase value. Exception No. 2: Where part of the concurrent load is resistance load, and where the disconnecting means is a switch rated in horsepower and current, the switch used shall be permitted to have a horsepower rating not less than the combined load of the motor(s) if the current rating of the switch is not less than the locked-rotor current of the motor(s) plus the resistance load. (2) Current Rating. The current rating of the disconnecting means shall not be less than 115 percent of the sum of all currents at the full-load condition determined in accordance with 430.110(C)(1). Exception: A listed nonfused motor-circuit switch having a horsepower rating equal to or greater than the equivalent horsepower of the combined loads, determined in accordance with 430.110(C)(1), shall be permitted to have a current rating less than 115 percent of the sum of all currents at the full-load condition. (3) Small Motors. For small motors not covered by Table 430.247, Table 430.248, Table 430.249, or Table 430.250, the locked-r