CHAPTER
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Conductor-Fill, Box-Fill, and Pull and Junction Box Sizing The NEC® recognizes many different types of raceways for the protection and routing of electrical conductors. Raceway installations may include conduit, wireways, device or junction boxes, and pull boxes. Each of these items has a limit to the number of conductors it may contain. When these installations are overfilled, the chances of damaging the conductor’s insulation increase. Damage to conductor insulation can be prevented by correctly sizing raceways, pull boxes, and junction boxes. Tables in chapter 9 of the NEC® are used to determine raceway-fill calculations. All tables in this chapter will refer to tables found in chapter 9 unless otherwise noted.
OBJECTIVES After completing this chapter, the learner will be able to do the following: • • • • • • •
Apply conductor-fill requirements of Table 1 of chapter 9 and the nine notes that follow it. Identify the key data used in Table 4 of chapter 9 to determine allowable fill. Explain how Table 5 of chapter 9 is used to calculate conductor fill. Explain why the conductor fill for conduit nipples is higher than for conduits longer in length. Identify the fill requirements for wireways. Explain how to size wireways. Identify the five steps used to determine the additional number of conductors allowed in a conduit that already contains a conductor. • List common items that are installed in boxes but that are not included in box-fill calculations. • Size the length of a pull box or junction box for straight pulls, angle pulls, and U-pulls.
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