NEC 610 covers details related to the installation of electric equipment and wiring requirements used in cranes, monorail hoists, and all runways. Cranes & hoists are considered as high torque requirement loads and constant movement of cranes or hoists requires the flexibility of power and control wiring which poses challenges to ensuring electrical safety.
NEC 610.3 covers details about special requirements for particular locations. NEC 610.3(A) provides details about Hazardous location classifications. All the equipment which are to be operated in hazardous locations shall conform to Article 500. Equipment operating in Class I, Class II, and Class III locations shall conform to Articles 501, 502, and 503 respectively. Class I locations relate to flammable gases or vapor locations, Class II locations relate to combustible dust, and Class III locations relate to the presence of easily ignitable fibers or flyings. NEC 610(B) covers details related to the provision of resistors for cranes and monorail hoists over readily combustible materials. Crane or monorail hoist resistors are provided in a well-ventilated cabinet made of noncombustible materials. It is permitted to be provided in a cage or cab enclosed on all sides by a non-combustible material from the floor to the point at least 150 mm (6 inches) above the top of the crane resistors.
NEC 610.11 covers wiring methods permitted for cranes & hoists. Type AC cable with an insulated grounding conductor is permitted to be an acceptable wiring method for cranes & hoists. NEC 610.11(A) permits that contact conductors shall not be enclosed in raceways. NEC 610.11(B) permits the short-length conductors that are exposed at electrical equipment connections such as resistors, collectors and similar equipment need not be enclosed in raceways. NEC 610.11(C) specifies that in case of any flexible connections to motors or similar equipment are necessary, flexible standard conductors shall be used. These conductors can be enclosed in flexible metal conduit, liquid-tight flexible metal or non-metallic conduit, multiconductor cable, or an approved nonmetallic enclosure (tubing). NEC 610.11(D) requires that in case of suspended push button stations connected from multi-conductor cable, proper support shall be provided for electrical conductors against any strain. In case of flexibility requirements for power and control of moving parts of cranes or hoists, listed festoon cable or a cord are to be provided which are suitable for the purpose.
NEC 610.13 covers details about the type of conductors and their requirements for provision in crane or hoist applications. NEC 610.13(A) requires that conductor(s) which are connected to hoist resistors or exposed to external heat shall be provided with a flame-resistant outer covering or has to be properly covered with flame-resistant tape for the individual conductors or as a group. NEC 610.13(B) requires that contact conductors along cable bridges and monorails are permitted to be bare conductors made of copper, steel, aluminum, or other alloys and combinations. NEC 610.13(C) specifies that where flexibility is required for power & control moving parts of the hoist, it is permitted to be provided with flexible cords or cables or festoon cables which are listed for the purpose. NEC 610.13(D) requires that the crane or hoist conductors provided for Class 1, Class 2, and Class 3 remote control and signaling circuits shall comply with NEC 725
NEC 610.14 covers ratings and sizing details of conductors associated with cranes and hoists. NEC 610.14(A) provides allowable ampacity details of conductors as per Table 610.14(A). NEC 610.14(B) requires that in case the hoist’s secondary resistor is separate from the controller, the minimum conductor size shall be calculated as per motor current multiplied by a factor ( as per Table 610.14(B)) and conductor size shall be selected as per Table 610.14(A). NEC 610.14(C) requires that the minimum conductor size external to hoist or crane motors shall be at least 16 AWG or greater. NEC 610.14(E) covers details about the calculation of motor loads. In the case of a hoist having a single motor, the minimum ampacity shall be as per 100% of the motor’s full load current rating. In the case of a crane or hoist having multi motors, the minimum ampacity of the power supply conductors shall be 100% rating of the largest motor in the group plus 50% of the nameplate current rating of the next largest motor or group of motors. Ampacity correction factors for the longest-time rated motors shall be applied.
NEC 610.21 covers details related to the installation of the crane or hoist contact conductors. NEC 610.21(A) requires that hoist runway contact conductors and bridge contact conductors shall be properly guarded against persons inadvertently touching energized parts carrying current. NEC 610.21(B) requires contact conductor wires shall be secured at both ends by strain insulators. NEC 610.21(C) requires that main contact conductors that are provided on the hoist runways shall be supported by means of insulator supports at not more than 6 mts (20 ft) intervals.