Print this page Voltage Drop Calculations
David A. Snyder, P.E.
Course Outline
This 3 PDH course includes common single-phase and three-phase voltage drop formulas, plus the derivation of the IEEE Standard 141 formula for Actual voltage drop. Dozens of illustrations, as well as many tables and examples, are included.
This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.
Learning Objective
At the end of this course, the student will learn:
- NEC recommendations on maximum voltage drops for feeders;
- NEC recommendations on maximum voltage drops for branch circuits;
- NEC 90;5(C) statement about explanatory information in the Code;
- Which columns to use in Table 9 of the NEC for voltage-drop calculations;
- Common formulas for approximate single-phase voltage drop calculations;
- Common formulas for approximate three-phase voltage drop calculations;
- The formula for Estimated line-to-neutral voltage drop;
- The formula for Estimated single-phase voltage drop;
- The formula for Estimated three-phase voltage drop;
- The purpose of the value 2 in single-phase voltage drop calculations;
- The purpose of the square root of three (√3) in balanced, three-phase voltage drop calculations;
- Derivation of the formula for line-to-neutral Error voltage;
- The formula for line-to-line Error voltage;
- The formula for Actual line-to-neutral voltage drop;
- The formula for Actual single-phase voltage drop; and
- The formula for Actual three-phase voltage drop.
Intended Audience
Any engineer, designer, contractor, or technician who is involved in the calculation of voltage drop and the selection of conductors for long runs will benefit from this course. It is assumed that the Reader is familiar with vector representation of three-phase voltages and currents.
Benefit to Attendees
Upon successful completion of the course, the Reader will have a thorough understanding of the differences between various voltage drop formulas, plus the inherent advantages, disadvantages, and limitations of those various types of calculations.
Course Introduction
Whenever current flows in a conductor, there is some amount of voltage drop. The magnitude of this voltage drop depends on the amount of current applied, characteristics and length of the cable, plus the power factor of the load. After the voltage drop, the amount of voltage remaining is all that is available to power the load. Will it be enough? If not, how can we size the conductors to provide enough voltage at the load?
Course Content
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Course Summary
There are many different types of formulas for voltage drop calculations. This course describes the similarities and differences between the various formulas and the advantages and disadvantages of each. The different columns in Table 9 of the NEC are discussed, as well as which of those values should be used in voltage drop calculations. The voltage drop phasor diagram from IEEE Standard 141 is explained and is used to derive the formula for Actual voltage drop.
Quiz
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.
DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.
