EC&M's Electrical Calculations Handbook
This is user-friendly, example-rich guide to problem solving strategies in engineering, design, installation, cost estimating, lighting design, and maintenance calculations in electrical work.
TABLE OF CONTENTS EC&M's Electrical Calculations Handbook
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 13.8-kilovolt (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 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...
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