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

(b) Secondary Resistor Conductors. Where the secondary resistor is separate from the controller, the minimum size of the conductors between controller and resistor shall be calculated by multiplying the motor secondary current by the appropriate factor from Table 610-14(b) and selecting a wire from Table 610-14(a). 70-646 NATIONAL ELECTRICAL CODE Table 610-14(a). Ampacities of Insulated Copper Conductors Used with Short-Time Rated Crane and Hoist Motors. Based on Ambient Temperature of 30°C (86°F). Up to Four Conductors in Raceway or Cable* Up to 3 ac** or 4 dc*Conductors in Raceway or Cable. Maximum Maximum Operating 75°C (167°F) 90°C (194°F) 125°C (257°F) Operating Temp. Temp. Size Types MTW, RH, Types TA, TBS, SA, Types FEP, FEPB, Size AWG RHW, THW, THWN, SIS, PFA, FEP, PFA, PFAH, SA, AWG (kcmil) XHHW, USE, ZW FEPB, RHH, THHN, TFE, Z, ZW (kcmil) XHHW, Z, zw 60 Min 30 Min 60 Min 30 Min 60 Min 30 Min 16 10 12 16 14 25 26 31 32 38 40 14 12 30 33 36 40 45 50 12 10 40 43 49 52 60 65 10 8 55 60 63 69 73 80 8 6 76 86 83 94 101 119 6 5 85 95 95 106 115 134 5 4 100 117 111 130 133 157 4 3 120 141 131 153 153 183 3 2 137 160 148 173 178 214 2 1 143 175 158 192 210 253 1 1/0 190 233 211 259 253 304 1/0 2/0 222 267 245 294 303 369 2/0 3/0 280 341 305 372 370 452 3/0 4/0 300 369 319 399 451 555 4/0 250 364 420 400 461 510 635 250 300 455 582 497 636 587 737 300 350 486 646 542 716 663 837 350 400 538 688 593 760 742 941 400 450 600 765 660 836 818 1042 450 500 660 847 726 914 896 1143 500 AMPACITY CORRECTION FACTORS Ambient For ambient temperatures other than 30°C (86°F), multiply the ampacities Ambient Temp. °C shown above by the appropriate factor shown below. Temp. °F 21-25 1.05 1.05 1.04 1.04 1.02 1.02 70-77 26-30 1.00 1.00 1.00 1.00 1.00 1.00 79-86 31-35 .94 .94 .96 .96 .97 .97 88-95 36-40 .88 .88 .91 .91 .95 .95 97-104 41-45 .82 .82 .87 .87 .92 .92 106-113 46-50 .75 .75 .82 .82 .89 .89 115-122 51-55 .67 .67 .76 .76 .86 .86 124-131 56-60 .58 .58 .71 .71 .83 .83 133-140 61-70 .33 .33 .58 .58 .76 .76 142-158 71-80 .41 .41 .69 .69 160-176 81-90 .61 .61 177-194 91-100 .51 .51 195-212 101-120 .40 .40 213-248 Other insulations shown in Table 310-13 and approved for the temperature and location shall be permitted to be substituted for those shown in Table 610-14(a). The allowable ampacities of conductors used with 15-minute motors shall be the 30-minute ratings increased by 12%. * For 5 to 8 simultaneously energized power conductors in raceway or cable, the ampacity of each power conductor shall be reduced to a value of 80% of that shown in the table. ** For 4 to 6 simultaneously energized 125°C (257°F) ac power conductors in raceway or cable, the ampacity of each power conductor shall be reduced to a value of 80% of that shown in the table. ARTICLE 610 - CRANES AND HOISTS 70-647 Table 610-14(b). Secondary Conductor Rating Factors Time in Seconds Ampacity of Wire in Percent of Full-Load On Off Secondary Current 5 75 35 10 70 45 15 75 55 15 45 65 15 30 75 15 15 85 Continuous Duty 110 (c) Minimum Size. Conductors external to motors and controls shall not be smaller than No. 16. Exception No. 1: No. 18 wire in multiple conductor cord shall be permitted for control circuits at not over 7 amperes. Exception No. 2: Wires not smaller than No. 20 shall be permitted for electronic circuits. (d) Contact Conductors. Contact wires shall have an ampacity not less than that required by Table 610-14(a) for 75°C (167°F) wire, and in no case shall they be smaller than the following: Distance Between End Strain Insulators or Clamp-type Intermediate Supports Size of Wire 0-30 feet No. 6 30-60 feet No. 4 Over 60 feet No. 2 For SI units: one foot = 0.3048 meter. (e) Calculation of Motor Load. (1) For one motor, use 100 percent of motor nameplate full-load ampere rating. (2) For multiple motors on a single crane or hoist, the minimum ampacity of the power supply conductors shall be the nameplate full-load I ampere rating of the largest motor or group of motors for any single crane motion, plus 50 percent of the nameplate full-load ampere rating of the next largest motor or group of motors, using that column of Table 610-14(a) that applies to the longest time-rated motor. (3) For multiple cranes and/or hoists supplied by a common conductor system, compute the motor minimum ampacity for each crane as defined in Section 610-14(e), add them together, and multiply the sum by the appropriate demand factor from Table 610-14(e). 70-648 NATIONAL ELECTRICAL CODE Table 610-14(e). Demand Factors Number of Cranes of Hoists Demand Factor 2 0.95 3 0.91 4 0.87 5 0.84 6 0.81 7 0.78 (f) Other Loads. Additional loads, such as heating, lighting, and air conditioning, shall be provided for by application of the appropriate sections of this Code. (g) Nameplate. Each crane, monorail, or hoist shall be provided with a visible nameplate marked with the maker's name, the rating in volts, frequency, number of phases, and circuit amperes as calculated in Sections 610-14(e) and (f). 610-15. Common Return. Where a crane or hoist is operated by more than one motor, a common-return conductor of proper ampacity shall be permitted. C. Contact Conductors 610-21. Installation of Contact Conductors. Contact conductors shall comply with (a) through (h) below. (a) Locating or Guarding Contact Conductors. Runway contact conductors shall be guarded, and bridge contact conductors shall be located or guarded in a manner that persons cannot inadvertently touch energized current-carrying parts. (b) Contact Wires. Wires that are used as contact conductors shall be secured at the ends by means of approved strain insulators and shall be so mounted on approved insulators that the extreme limit of displacement of the wire will not bring the latter within less than 1½ inches (38 mm) from the surface wired over. (c) Supports Along Runways. Main contact conductors carried along runways shall be supported on insulating supports placed at intervals not exceeding 20 feet (6.1 m). Exception: Supports for grounded rail conductors as provided in (f) below shall not be required to be of the insulating type. Such conductors shall be separated not less than 6 inches (152 mm) other than for monorail hoists where a spacing of not less than 3 inches (76 mm) shall be permitted. Where necessary, intervals between insulating supports shall be permitted to be increased up to 40 feet (12.2 m), the separation between conductors being increased proportionately. ARTICLE 610 - CRANES AND HOISTS 70-649 (d) Supports on Bridges. Bridge wire contact conductors shall be kept at least 2½ inches (64 mm) apart, and, where the span exceeds 80 feet (24.4 m), insulating saddles shall be placed at intervals not exceeding 50 feet (15.2 m). (e) Supports for Rigid Conductors. Conductors along runways and crane bridges, that are of the rigid type specified in Section 610-13, Exception No. 2 and not contained within an approved enclosed assembly, shall be carried on insulating supports spaced at intervals of not more than eighty times the vertical dimension of the conductor, but in no case greater than 15 feet (4.57 m), and spaced apart sufficiently to give a clear electrical separation of conductors or adjacent collectors of not less than 1 inch (25.4 mm). (f) Track as Circuit Conductor. Monorail, tramrail, or crane-runway tracks shall be permitted as a conductor of current for one phase of a 3-phase, alternating-current system furnishing power to the carrier, crane, or trolley, provided all of the following conditions are met: (1) The conductors supplying the other two phases of the power supply are insulated. (2) The power for all phases is obtained from an insulating transformer. (3) The voltage does not exceed 300 volts. (4) The rail serving as a conductor is effectively-grounded at the transformer and also shall be permitted to be grounded by the fittings used for the suspension or attachment of the rail to a building or structure. (g) Electrical Continuity of Contact Conductors. All sections of contact conductors shall be mechanically joined to provide a continuous electrical connection. (h) Not to Supply Other Equipment. Contact conductors shall not be used as feeders for any equipment other than the crane or cranes that they are primarily designed to serve. 610-22. Collectors. Collectors shall be so designed as to reduce to a minimum sparking between them and the contact conductor; and, where operated in rooms used for the storage of easily ignitible combustible fibers and materials, they shall comply with Section 503-13. D. Disconnecting Means 610-31. Runway Conductor Disconnecting Means. A disconnecting means having a continuous ampere rating not less than that computed in Sections 610-14(e) and (f) shall be provided between the runway contact conductors and the power supply. Such disconnecting means shall consist shall: of a motor circuit switch or circuit breaker. This disconnecting means (1) Be readily accessible and operable from the ground or floor level. (2) Be arranged to be locked in the open position. (3) Open all ungrounded conductors simultaneously. (4) Be placed within view of the crane or hoist and the runway contact conductors. 70-650 NATIONAL ELECTRICAL CODE 610-32. Disconnecting Means for Cranes and Monorail Hoists. A motor circuit switch or circuit breaker arranged to be locked in the open position shall be provided in the leads from the runway contact conductors or other power supply on all cranes and monorail hoists. Exception: Where a monorail hoist or hand-propelled crane bridge installation meets all of the following, the disconnect shall be permitted to be omitted. a. The unit is floor controlled. b. The unit is within view of the power supply disconnecting means. c. No fixed work platform has been provided for servicing the unit. Where the disconnecting means is not readily accessible from the crane or monorail hoist operating station, means shall be provided at the operating station to open the power circuit to all motors of the crane or monorail hoist. 610-33. Rating of Disconnecting Means. The continuous ampere rating of the switch or circuit breaker required by Section 610-32 shall not be less than 50 percent of the combined short-time ampere rating of the motors, nor less than 75 percent of the sum of the short-time ampere rating of the motors required for any single motion. E. Overcurrent Protection 610-41. Feeders, Runway Conductors. The runway supply conductors and main contact conductors of a crane or monorail shall be protected by an overcurrent device(s) that shall not be greater than the largest rating or setting of any branch-circuit protective device, plus the sum of the nameplate ratings of all the other loads with application of the demand factors from Table 610-14(e). 610-42. Branch-Circuit Short-Circuit and Ground-Fault Protection. Branch circuits shall be protected as follows: (a) Fuse or Circuit Breaker Rating. Crane, hoist, and monorail hoist motor branch circuits shall be protected by fuses or inverse-time circuit breakers having a rating in accordance with Table 430-152. Taps to control circuits shall be permitted to be taken from the load side of a branch-circuit protective device, provided each tap and piece of equipment is properly protected. Exception No. 1: When two or more motors operate a single motion, the sum of their nameplate current ratings shall be considered as a single motor current in the above calculations. Exception No. 2: Two or more motors shall be permitted to be connected to the same branch circuit if no tap conductor to an individual motor has an ampacity less than one-third that of the branch circuit and if each motor is protected from overload according to Section 610-43. (b) Taps to Brake Coils. Taps to brake coils do not require separate overcurrent protection. ARTICLE 610 - CRANES AND HOISTS 70-651 610-43. Motor and Branch-Circuit Overload Protection. Each motor, motor control, and branch-circuit conductor shall be protected from overload by one of the following means: (1) A single motor shall be considered as protected where the branchcircuit overcurrent device meets the rating requirements of Section 610-42. (2) Overload relay elements in each ungrounded circuit conductor, with all relay elements protected from short circuit by the branch-circuit protection. (3) Thermal sensing device(s), sensitive to motor temperature or to temperature and current that are thermally in contact with the motor winding(s). A hoist or trolley is considered to be protected if the sensing device is connected in the hoist's upper limit switch circuit so as to prevent further hoisting during an overload condition of either motor. Exception No. 1: If the motor is manually controlled, with spring return controls, the overload protective device shall not be required to protect the motor against stalled rotor conditions. Exception No. 2: Where two or more motors drive a single trolley, truck, or bridge and are controlled as a unit by a single set of overload devices with a rating equal to the sum of their rated full-load currents. A hoist or trolley shall be considered to be protected if the sensing device is connected in the hoist's upper limit switch circuit so as to prevent further hoisting during an overtemperature condition of either motor. Exception No. 3: Hoists and monorail hoists and their trolleys that are not used as part of an overhead traveling crane shall not require individual motor overload protection, provided the largest motor does not exceed 7½ horsepower and all motors are under manual control of the operator. F. Control 610-51. Separate Controllers. Each motor shall be provided with an individual controller. Exception No. 1: Where two or more motors drive a single hoist, carriage, truck, or bridge, they shall be permitted to be controlled by a single controller. Exception No. 2: One controller shall be permitted to be switched between motors, provided: a. The controller shall have a horsepower rating that shall not be lower than the horsepower rating of the largest motor. b. Only one motor is operated at one time. 610-53. Overcurrent Protection. Conductors of control circuits shall be protected against overcurrent. Control circuits shall be considered as protected by overcurrent devices that are rated or set at not more than 300 percent of the ampacity of the control conductors. Exception No. 1: Taps to control transformers shall be considered as protected where the secondary circuit is protected by a device rated or set at not more than 200 percent of the rated secondary current of the transformer and not more than 200 percent of the ampacity of the control circuit conductors. 70-652 NATIONAL ELECTRICAL CODE Exception No. 2: Such conductors shall be considered as being properly protected by the branch-circuit overcurrent devices where the opening of the control circuit would create a hazard, as for example, the control circuit of a hot metal crane. 610-55. Limit Switch. A limit switch or other device shall be provided to prevent the load block from passing the safe upper limit of travel of all hoisting mechanisms. 610-57. Clearance. The dimension of the working space in the direction of access to live parts that are likely to require examination, adjustment, servicing, or maintenance while energized shall be a minimum of 2½ feet (762 mm). Where controls are enclosed in cabinets, the door(s) shall either open at least 90 degrees or be removable. G. Grounding 610-61. Grounding. All exposed noncurrent-carrying metal parts of cranes, monorail hoists, hoists, and accessories including pendant controls shall be metallically joined together into a continuous electrical conductor so that the entire crane or hoist will be grounded in accordance with Article 250. Moving parts, other than removable accessories or attachments, having metal-to-metal bearing surfaces shall be considered to be electrically connected to each other through the bearing surfaces for grounding purposes. The trolley frame and bridge frame shall be considered as electrically grounded through the bridge and trolley wheels and its respective tracks unless local conditions, such as paint or other insulating material, prevent reliable metal-to-metal contact. In this case, a separate bonding conductor shall be provided.