The most significant factor in crane and hoist safety, after structural integrity, is electrical safety. All the referenced standards support this fact either directly or indirectly by the amount of definition and space provided for electrical systems' controls, operations, and maintenance.

6.2.1 NEC GENERAL REQUIREMENTS

Basic installation and wiring safety requirements for cranes and hoists are given in NEC Article 610¹. Electrical designers and maintenance personnel should thoroughly understand these requirements and their intent. Some of the more significant requirements are the following:

1. Cranes and hoists operated in hazardous (classified) locations shall conform to NEC Article 500.

2. When the crane is operated above readily combustible materials, the resistors must be located in a well-ventilated cabinet constructed of noncombustible material and constructed so that they will not emit flames or molten metal. See the exception (and requirements) that applies to certain cabinets made of noncombustible materials.

3. Cranes and hoists operating on electrolytic cell lines have special requirements, as given in NEC Section 668-32.

a. Grounding is not required for conductive surfaces of cranes and hoists that enter the working zone of a cell line, and the parts that come in contact with an energized cell or attachments shall be insulated from ground.

¹ See Appendix D, Reference Matrix.

b. Remote controls that may introduce hazardous conditions into the cell line working zone shall employ one or more of the following:

(1) Isolated and ungrounded control circuit in compliance with NEC Section 668-21 (a)

(2) Nonconductive rope operator

(3) Pendant pushbutton with either non-conductive support and surfaces or ungrounded exposed surfaces.

(4) Radio

6.2.2 DISCONNECTING MEANS

The disconnecting means provided for cranes and hoists may consist of two or more lock-open-type motor circuit switches or circuit breakers. Article 610, Part D, of the NEC, "Disconnecting Means," and the installation and operating plans should be studied carefully to determine the disconnecting means requirements and locations. The two basic disconnects to consider are:

1. The runway conductor (conductors run along a crane runway for power or control) disconnect which shall:

a. Be readily accessible or operable from the ground or floor level per NEC Section 61031(1)

b. Be lockable in the open position per NEC Section 610-31(2)

c. Open all ungrounded conductors simultaneously per NEC Section 610-31(3)

d. Be placed in view of the crane or hoist and the runway conductors per NEC Section 61031(4).

2. The crane and hoist disconnect which shall be provided in the leads from the runway contact conductors or other power supply unless all the following requirements are met:

a. The unit is ground or floor level controlled per NEC Section 610-32, Exception

b. The unit is within view of the power supply disconnecting means per NEC Section 61032, Exception

c. No fixed work platform has been provided for servicing the unit per NEC Section 61032, Exception.

See Figure 6-1 (a) and (b) for a detailed illustration of the rules pertaining to the disconnecting means for electric cranes and hoists.

Figure 6-1(a). An additional control switch or a remote control switch is required if the second disconnecting means is not accessible to the operator.

Figure 6-1(b). Second disconnect not required. A monorail hoist does not require a disconnecting means in the leads to the hoist machinery if it is controlled from the floor, if it is within view of the power supply disconnect, and if there is no work platform provided to service the hoist machinery.