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-voltage starting for polyphase induction motor wye windings. This requires a specific type of motor controller and a delta-wired motor with all leads brought out to the terminal box. This method of starting finds wide application in certain compressors used for air conditioning and where the driven...

-voltage starting for polyphase induction motor wye windings. This requires a specific type of motor controller and a delta-wired motor with all leads brought out to the terminal box. This method of starting finds wide application in certain compressors used for air conditioning and where the driven machinery is allowed to start unloaded. During starting, the windings are arranged in a wye configuration. The wye-start configuration results in a reduced starting voltage of a mathematical ratio of 1/√3 = 0.5774, or 58 percent of the full line voltage, which results in approximately 58 percent starting current and about one-third of the normal starting torque. Once the motor attains speed, the windings are reconfigured to run as delta, giving full line voltage to the individual windings, which allows the motor to have full torque capability. Since the delta-connected motor load is 58 percent of the rated load current and the conductors are sized at 125 percent of the motor full-load current, the conductors would be sized at 1.25 times 58 percent, or 72 percent of the motor full-load current rating. In the following exhibit, conductors from terminals T1, T2, and T3 to the motor, as well as the conductors from terminals T4, T5, and T6 to the motor, are all sized at 58 percent of the full-load current used to size the conductors that supply L1, L2, and L3. During START, contacts 1M and S are closed and contacts 2M are open. During RUN, contacts 1M and 2M are closed and the S contacts are open. Part-Winding Motor. For a part-winding connected motor, the ampacity of the branch-circuit conductors on the line side of the controller shall not be less than 125 percent of the motor full-load current as determined by 430.6(A)(1). The ampacity of the conductors between the controller and the motor shall not be less than 62.5 percent of the motor full-load current rating as determined by 430.6(A)(1). Informational Note: The multiplier of 62.5 percent is obtained by multiplying 50 percent by 1.25. ENHANCED CONTENT Collapse A part-winding motor starter supplies power to partial sections of the primary winding of the motor. When the motor is running, load on the conductors will be approximately 50 percent of motor full-load current. The 62.5 percent of the full-load current rating is 125 percent of the running current with all windings connected. Other Than Continuous Duty. Conductors for a motor used in a short-time, intermittent, periodic, or varying duty application shall have an ampacity of not less than the percentage of the motor nameplate current rating shown in Table 430.22(E), unless the authority having jurisdiction grants special permission for conductors of lower ampacity. Table 430.22(E) Duty-Cycle Service Classification of Service Nameplate Current Rating Percentages 5-Minute Rated Motor 15-Minute Rated Motor 30- & 60- Minute Rated Motor Contin- uous Rated Motor Short-time duty operating valves, raising or lowering rolls, etc. 110 120 150 — Intermittent duty freight and passenger elevators, tool heads, pumps, drawbridges, turntables, etc. (for arc welders, see 630.11) 85 85 90 140 Periodic duty rolls, ore- and coal-handling machines, etc. 85 90 95 140 Varying duty 110 120 150 200 Note: Any motor application shall be considered as continuous duty unless the nature of the apparatus it drives is such that the motor will not operate continuously with load under any condition of use. ENHANCED CONTENT Collapse Most motor applications are continuous duty. For motors that are not continuous duty, the motor nameplate currents and Table 430.22(E) are used to determine the branch-circuit ampacity. Branch-circuit conductors for a motor with a rated horsepower used for 5-minute short-time duty service are permitted to be sized smaller than for the same motor with a 60-minute rating, due to the cooling intervals between operating periods. For example, a 5-minute rated motor will run for 5 minutes and then be off for 55 minutes. See also the definitions of the terms continuous duty, intermittent duty, periodic duty, short-time duty, and varying duty in Article 100. Separate Terminal Enclosure. The conductors between a stationary motor rated 1 hp or less and the separate terminal enclosure permitted in 430.245(B) shall be permitted to be smaller than 14 AWG but not smaller than 18 AWG, provided they have an ampacity as specified in 430.22. Conductors for Small Motors. Conductors for small motors shall not be smaller than 14 AWG unless otherwise permitted in 430.22(G)(1) or (G)(2). 18 AWG Copper. 18 AWG individual copper conductors installed in a cabinet or enclosure, copper conductors that are part of a jacketed multiconductor cable assembly, or copper conductors in a flexible cord shall be permitted, under either of the following sets of conditions: The circuit supplies a motor with a full-load current rating, as determined by 430.6(A)(1), of greater than 3.5 amperes, and less than or equal to 5 amperes, and all the following conditions are met: The circuit is protected in accordance with 430.52. The circuit is provided with maximum Class 10 or Class 10A overload protection in accordance with 430.32. Overcurrent protection is provided in accordance with 240.4(D)(1)(2). The circuit supplies a motor with a full-load current rating, as determined by 430.6(A)(1), of 3.5 amperes or less, and all the following conditions are met: The circuit is protected in accordance with 430.52. The circuit is provided with maximum Class 20 overload protection in accordance with 430.32. Overcurrent protection is provided in accordance with 240.4(D)(1)(2). 16 AWG Copper. 16 AWG individual copper conductors installed in a cabinet or enclosure, copper conductors that are part of a jacketed multiconductor cable assembly, or copper conductors in a flexible cord shall be permitted under either of the following sets of conditions: The circuit supplies a motor with a full-load current rating, as determined by 430.6(A)(1), of greater than 5.5 amperes, and less than or equal to 8 amperes, and all the following conditions are met: The circuit is protected in accordance with 430.52. The circuit is provided with maximum Class 10 or Class 10A overload protection in accordance with 430.32. Overcurrent protection is provided in accordance with 240.4(D)(2)(2). The circuit supplies a motor with a full-load current rating, as determined by 430.6(A)(1), of 5.5 amperes or less, and all the following conditions are met: The circuit is protected in accordance with 430.52. The circuit is provided with maximum Class 20 overload protection in accordance with 430.32. Overcurrent protection is provided in accordance with 240.4(D)(2)(2). 430.23 Wound-Rotor Secondary. (A) Continuous Duty. For continuous duty, the conductors connecting the secondary of a wound-rotor ac motor to its controller shall have an ampacity not less than 125 percent of the full-load secondary current of the motor. Other Than Continuous Duty. For other than continuous duty, these conductors shall have an ampacity, in percent of full-load secondary current, not less than that specified in Table 430.22(E). Resistor Separate from Controller. Where the secondary resistor is separate from the controller, the ampacity of the conductors between controller and resistor shall not be less than that shown in Table 430.23(C). Table 430.23(C) Secondary Conductor Resistor Duty Classification Ampacity of Conductor in Percent of Full-Load Secondary Current Light starting duty 35 Heavy starting duty 45 Extra-heavy starting duty 55 Light intermittent duty 65 Medium intermittent duty 75 Heavy intermittent duty 85 Continuous duty 110 430.24 Several Motors or a Motor(s) and Other Load(s). Conductors supplying several motors, or a motor(s) and other load(s), shall have an ampacity not less than the sum of each of the following: (1) 125 percent of the full-load current rating of the highest rated motor, as determined by 430.6(A) Sum of the full-load current ratings of all the other motors in the group, as determined by 430.6(A) 100 percent of the noncontinuous non-motor load 125 percent of the continuous non-motor load. Informational Note: See Informative Annex D, Example No. D8. Exception No. 1: Where one or more of the motors of the group are used for short-time, intermittent, periodic, or varying duty, the ampere rating of such motors to be used in the summation shall be determined in accordance with 430.22(E). For the highest rated motor, the greater of either the ampere rating from 430.22(E) or the largest continuous duty motor full-load current multiplied by 1.25 shall be used in the summation. Exception No. 2: The ampacity of conductors supplying motor-operated fixed electric space-heating equipment shall comply with 424.4(B). Exception No. 3: Where the circuitry is interlocked so as to prevent simultaneous operation of selected motors or other loads, the conductor ampacity shall be permitted to be based on the summation of the currents of the motors and other loads to be operated simultaneously that results in the highest total current. ENHANCED CONTENT Collapse As illustrated below, the requirements of Article 210 and Article 430 apply where motors are connected to a 15- or 20-ampere branch circuit that also supplies lighting or other appliance loads. Motors rated less than 1 horsepower may be connected to these circuits, and they must be provided with overload protective devices unless the motors are not permanently installed, are started manually, and are within sight of the controller location. See also 430.32(B) and (C) and 430.53(A) for additional information on the installation of motors (1 horsepower or less). Where branch circuits or feeders serve motors and/or other electrical loads, the highest rating or setting of the branch circuit or feeder short-circuit and ground-fault protective devices for the minimum-size branch circuit or feeder conductor permitted by 430.24 is specified in 430.62. Where two or more motors are started simultaneously, the heaviest load that a feeder will ever be required to carry occurs when the largest motor is started, and all the other motors supplied by the same feeder are running and delivering their full-rated horsepower. This requirement and those of 430.62 for the short-circuit and ground-fault protection of the branch circuit or feeder are based on the principle that the conductors should be sized to have an ampacity equal to 125 percent of the full-load current of the largest motor plus the full-load currents of all other motors and all other loads supplied by the feeder. Where the conductors are branch-circuit conductors to multi-motor equipment, 430.53 specifies the maximum rating of the branch-circuit short-circuit and ground-fault protective device, and 430.7(D)(1) requires the maximum ampere rating of the short-circuit and ground-fault protective device to be marked on multi-motor equipment. 430.25 Multimotor and Combination-Load Equipment. The ampacity of the conductors supplying multimotor and combination-load equipment shall not be less than the minimum circuit ampacity marked on the equipment in accordance with 430.7(D). Where the equipment is not factory-wired and the individual nameplates are visible in accordance with 430.7(D)(2), the conductor ampacity shall be determined in accordance with 430.24. ENHANCED CONTENT Collapse Computing the load for the minimum allowable conductor size for a combination lighting (or lighting and appliance) load and motor load involves determining the lighting load in accordance with Article 220 (and other applicable articles and sections), the appliance load in accordance with Article 422, and the motor load in accordance with 430.22 (single motor) or 430.24 (two or more motors). The lighting load and the motor load are added together to determine the minimum conductor ampacity. 430.26 Feeder Demand Factor. Where reduced heating of the conductors results from motors operating on duty-cycle, intermittently, or from all motors not operating at one time, the authority having jurisdiction may grant permission for feeder conductors to have an ampacity less than specified in 430.24, provided the conductors have sufficient ampacity for the maximum load determined in accordance with the sizes and number of motors supplied and the character of their loads and duties. Informational Note: Demand factors determined in the design of new facilities can often be validated against actual historical experience from similar installations. 430.27 Capacitors with Motors. Where capacitors are installed in motor circuits, conductors shall comply with 460.8 and 460.9. 430.28 Feeder Taps. Feeder tap conductors shall have an ampacity not less than that required by Part II, shall terminate in a branch-circuit protective device, and, in addition, shall meet one of the following requirements: (1) Be enclosed either by an enclosed controller or by a raceway, be not more than 3.0 m (10 ft) in length, and, for field installation, be protected by an overcurrent device on the line side of the tap conductor, the rating or setting of which shall not exceed 1000 percent of the tap conductor ampacity Have an ampacity of at least one-third that of the feeder conductors, be suitably protected from physical damage or enclosed in a raceway, and be not more than 7.5 m (25 ft) in length Have an ampacity not less than the feeder conductors Exception: Feeder taps over 7.5 m (25 ft) long. In high-bay manufacturing buildings [over 11 m (35 ft) high at walls], where conditions of maintenance and supervision ensure that only qualified persons service the systems, conductors tapped to a feeder shall be permitted to be not over 7.5 m (25 ft) long horizontally and not over 30.0 m (100 ft) in total length where all of the following conditions are met: (1) The ampacity of the tap conductors is not less than one-third that of the feeder conductors. (2) The tap conductors terminate with a single circuit breaker or a single set of fuses complying with (1) Part IV, where the load-side conductors are a branch circuit, or (2) Part V, where the load-side conductors are a feeder. (3) The tap conductors are suitably protected from physical damage and are installed in raceways. (4) The tap conductors are continuous from end-to-end and contain no splices. (5) The tap conductors shall be 6 AWG copper or 4 AWG aluminum or larger. (6) The tap conductors shall not penetrate walls, floors, or ceilings. (7) The tap shall not be made less than 9.0 m (30 ft) from the floor. ENHANCED CONTENT Collapse For a single motor load, the tap conductors are sized the same as the motor branch-circuit conductors — that is, according to 430.22, which requires that motor branch-circuit conductors be sized at least 125 percent of the full-load current value for the motor given in Tables 430.248 through 430.250. The table value, rather than the nameplate value, is the full-load current used for conductor sizing according to 430.6(A). The tap conductors must terminate in a set of fuses or a circuit breaker, thus limiting the load on the tap conductors. The reduced-size tap conductors are protected from overload by the overcurrent device where the tap conductors terminate but are protected from short circuit and ground fault only from the feeder overcurrent device. A tap conductor installation also must meet the additional requirements associated with their tap conductor distance limits, that is, 10 feet, 25 feet, or, by exception, 100 feet. The requirements for tap conductors that supply motor loads are similar to the basic tap requirements found in 240.21. See also 430.53(D) and its enhanced content for additional information concerning a tap supplying a single motor in a group installation. 430.29 Constant Voltage Direct-Current Motors — Power Resistors. Conductors connecting the motor controller to separately mounted power accelerating and dynamic braking resistors in the armature circuit shall have an ampacity not less than the value calculated from Table 430.29 using motor full-load current. If an armature shunt resistor is used, the power accelerating resistor conductor ampacity shall be calculated using the total of motor full-load current and armature shunt resistor current. Armature shunt resistor conductors shall have an ampacity of not less than that calculated from Table 430.29 using rated shunt resistor current as full-load current. Table 430.29 Conductor Rating Factors for Power Resistors Time in Seconds Ampacity of Conductor in Percent of Full-Load Current On Off 5 75 35 10 70 45 15 75 55 15 45 65 15 30 75 15 15 85 Continuous Duty 110 Part III. Motor and Branch-Circuit Overload Protection 430.31 General. Part III specifies overload devices intended to protect motors, motor-control apparatus, and motor branch-circuit conductors against excessive heating due to motor overloads and failure to start. Informational Note No. 1: See Informative Annex D, Example D8. Informational Note No. 2: See Article 100for the definition of Overload. Where Hazard Exists. These provisions shall not require overload protection where a power loss would cause a hazard, such as in the case of fire pumps. Informational Note: See 695.7 for protection of fire pump supply conductors. Not Over 1000 Volts. Part III shall not apply to motor circuits rated over 1000 volts, nominal. Informational Note: See Part XI for over 1000 volts, nominal. ENHANCED CONTENT Collapse Overload protection is not designed or may not be capable of breaking short-circuit current or ground-fault current. 430.32 Continuous-Duty Motors. (A) More Than 1 Horsepower. Each motor used in a continuous duty application and rated more than 1 hp shall be protected against overload by one of the means in 430.32(A)(1) through (A)(4). Separate Overload Device. A separate overload device that is responsive to motor current. This device shall be selected to trip or shall be rated at no more than the following percent of the motor nameplate full-load current rating: Motors with a marked service factor 1.15 or greater 125% Motors with a marked temperature rise 40°C or less 125% All other motors 115% Modification of this value shall be permitted as provided in 430.32(C). For a multispeed motor, each winding connection shall be considered separately. Where a separate motor overload device is connected so that it does not carry the total current designated on the motor nameplate, such as for wye-delta starting, the proper percentage of nameplate current applying to the selection or setting of the overload device shall be clearly designated on the equipment, or the manufacturer’s selection table shall take this into account. Informational Note: See 460.9 for power factor correction capacitors that are installed on the load side of the motor overload device. ENHANCED CONTENT Collapse To protect a motor from an overload, the motor nameplate full-load current is used to select the overload protection rather than the full-load current values from Tables 430.248 through 430.250, which are used to select the feeder and branch-circuit wiring. A continuous-duty motor with a marked service factor of 1.15 or greater or with a marked temperature rise of 40°C or less can carry a 25-percent overload for an extended period without damage to the motor. Motors with a service factor of less than 1.15 or those with a marked temperature rise greater than 40°C might be incapable of withstanding a prolonged overload, where the motor overload protective device opens the circuit if the motor continues to draw 115 percent of its rated full-load current. A “continuous-duty motor” is not the same as a “continuous load.” The duty of a motor is determined by the application of the motor as defined in Article 100 under the five various types of duty: continuous duty, intermittent duty, periodic duty, short-time duty, and varying duty. Thermal Protector or Electronically Protected. A thermal protector integral with the motor shall be approved for use with the motor it protects on the basis that it will prevent dangerous overheating of the motor due to overload and failure to start. An electronically protected motor shall be approved for use on the basis that it will prevent dangerous overheating due to the failure of the electronic control, overload, or failure to start the motor. The ultimate trip current of a thermally or electronically protected motor shall not exceed the following percentage of motor full-load current given in Table 430.248, Table 430.249, and Table 430.250: Motor full-load current 9 amperes or less 170% Motor full-load current from 9.1 to, and including, 20 amperes 156% Motor full-load current greater than 20 amperes 140% If the motor current-interrupting device is separate from the motor and its control circuit is operated by a protective device integral with the motor, it shall be arranged so that the opening of the control circuit will result in interruption of current to the motor. ENHANCED CONTENT Collapse The thermal protector illustrated below is located inside the motor housing and is connected in series with the motor winding by a set of normally closed contacts attached to a bimetallic disk. The thermal protector heating coil causes the disk to heat rapidly and snap the contacts open to protect the motor windings. After the circuit opens and the motor has cooled to a normal temperature, the contacts automatically close and restart the motor. Where automatic restart is not desirable, the protective device is designed so that it must be returned to the closed position by a manually controlled reset as required by 430.43. (Courtesy of Sensata Technologies) In lieu of electromechanical protective devices, 430.32(A) 2) also recognizes the use of electronic means to protect a motor and motor circuit conductors from overload (overheating) conditions due to excessive driven machinery loading or failure to start. Electronically protected motors must be marked in accordance with 430.7(A)(16). Integral with Motor. A protective device integral with a motor that will protect the motor against damage due to failure to start shall be permitted if the motor is part of an approved assembly that does not normally subject the motor to overloads. Larger Than 1500 Horsepower. For motors larger than 1500 hp, a protective device having embedded temperature detectors that cause current to the motor to be interrupted when the motor attains a temperature rise greater than marked on the nameplate in an ambient temperature of 40°C.