Electrical Design and Layout Calculations Nhiều thiết kế và bố trí các vấn đề phát sinh hàng ngày trong công việc của các kỹ sư điện và nhà thiết kế, chẳng hạn như: kích thước tối thiểu là gì thẳng thông qua hộp kéo, kéo một hộp góc, hoặc một hộp đường giao nhau? 480/277-volt (V) bảng điều khiển có thể được đặt gần một bức tường? Gần nhau có thể hai đối lập 13,8-kilovolt (kV) bố trí thiết bị chuyển mạch được đặt? Làm thế nào gần nhau Knockouts có thể đấm mà không gây ra locknuts thể. | Chapter 14 Electrical Design and Layout Calculations Many design and layout issues arise daily in the work of electrical engineers and designers such as What are the minimum dimensions of a straight-through pull box an angle pull box or a junction box How close to a wall can a 480 277-volt V panel be placed How close together can two opposing kV switchgear layouts be placed How close together can knockouts be punched without causing locknuts to physically overlap and interfere with one another What minimum phase-to-phase and phase-to-ground dimensions must be maintained when constructing an auxiliary wireway This chapter provides convenient answers to these questions by providing the rules for each along with completed go by calculations that engineers and designers can use as templates for their specific calculations simply by changing certain values. Straight-Through Pull Box in a Conduit System When wires are drawn through a conduit the friction between the conductor insulation and the conduit can become 357 Copyright 2001 by The McGraw-Hill Companies Inc. Click here for Terms of Use. 358 Chapter Fourteen too great damaging the conductors. Therefore sometimes intermediate pulling points are required within what would otherwise be a continuous conduit run. When wires are pulled in a conduit run that contains pull boxes the wires are completely drawn through and out of the open cover of the pull box and then are refed into the next part of the conduit run. As most of the wire length is pulled into the next part of the conduit run the wire loop at the cover of the pull box forms an increasingly smaller radius until the wire is all in the box. The minimum bending radius of the conductor the size of conduit that each conductor circuit will normally fit within and the possibility of physically damaging the conductor on the sharp edges of the pull box flanges have been considered in specifying the minimum dimensions of a straight-through pull box which is
