National Electrical Code Articles and Information

National Electrical Code Top Ten Tips: Article 610, Cranes and Hoists

1. In Chapter 6, Article 610 is the first that really gets into a meaty topic, and it's one many industrial electricians must understand. The other three Articles preceding it are 600 (Electric Signs and Outline Lighting), Article 604 (Manufactured Wiring Systems), and Article 605 (Office Furnishings). While 600 seems like a lot of detail for electric signs, the other two Articles are quite short.
    
2. What is a crane or hoist? Most of us know what these are, but if you don't then here's a working definition applicable to Article 610. A hoist is a motor-driven mechanical device used to lift an object deemed too heavy or awkward for humans to lift. This is very similar to the Article 100 definition of "crane", which applies to boats. A hoist can move the load up or down. A crane is a hoist that also provides horiztonal movement.
    
3. Since (for the purposes of Articl 610) cranes and hoists are motor-driven devices, Article 610 is really about a particular motor application. Article 430 provides the requirements for motors. Table 430.5 lists “Other Articles,” based on equipment/occupancy. Article 610 is one of those other Articles, and it provides the requirements for cranes and hoists. Article 610 is an “amend and append” of Chapters 1 -4, as they pertain to cranes and hoists.
    
4. Don't use solid conductors for flexible connections. Use flexible stranded conductors [610.11(C)].
    
5. Conductors leaving raceways or cables must be properly protected from abrasion via a separately bushed hole or a bushing in lieu of a box [610.12].
    
6. You can use only the conductors specified in Table 610.14(A), and there aren't very many. Which conductor you use, and which part of the table you can apply for ampacity, depends on several factors. These factors are identified in the table notes, in 610.13, and in 610.14.
    
7. While it may not be advisable from an engineering standpoint (though it might), you can use a common return conductor in cases where two or more motors operate a crane or hoist [610.15]. Just make sure it is of the proper ampacity.
    
8. Contact conductors are tricky, because they must move. The requirements are in Part III. The main consideration is the protection of these conductors from mechanical damage while they are moving. Proper support, for example, is critical. That's why 610.21 has requirements for the supports along runways, for those on bridges, and for rigid conductors. These are minimums, it costs hardly anything to exceed the requirements.
    
9. You need a disconnecting means for the runway contact conductors, and you need a disconnecting means for cranes and monorail hoists [610.32]. It must be lockable open. Make sure you orient it such that the operator can pull the handle down with his left hand while standing to the left of the disconnect (out of the blast path).
    
10. The overcurrent protection calculations are the same as for other motors, except you must use the demand factors of Table 610.14(E) and comply with a few other Article 610 amendments. The requirements for overcurrent protection are in Part V (610.41 through 610.43).