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Voltage drop practice

Circular mils, volts dropped, percent of nominal and the voltage left at the load.

Voltage drop on a run

Problem

Problem code VD-00J5N4

NEC 2023Worked to the 2023 edition as used by this site's calculators; your exam may use another edition. The 2026 edition renumbered some articles, so check any number against the edition your exam uses.

A 240 V single-phase circuit feeds a 40 A load 190 ft from the panel (one-way length) on 8 AWG copper conductors. Using the circular-mil method with K = 12.9 for copper, find the voltage drop, the drop as a percent and the voltage at the load.

System
240 V single-phase
Load
40 A
One-way length
190 ft
Conductor
8 AWG copper
K
12.9 (copper)
  1. cmil

    Must match

  2. V

    Within ±0.05 V or ±1%, whichever is larger

  3. %

    Within ±0.05% or ±1%, whichever is larger

  4. V

    Within ±0.1 V

Every problem has a code. The same code always gives the same problem and key.

Check the numbers in the voltage drop calculator, which gives the same answers from the same functions.

What these problems are based on

Every problem is generated by this site's own calculators from the published tables they already use. No question is taken from an exam, a code book or a prep book, and no code text is quoted.

Worked to the 2023 edition as used by this site's calculators; your exam may use another edition. The 2026 edition renumbered some articles, so check any number against the edition your exam uses.

Assumptions

  • VD = 2 × K × I × L ÷ CM for single phase and 1.732 × K × I × L ÷ CM for three phase, with L the one-way length.
  • Conductor reactance and power factor are ignored, as in the site's voltage drop calculator.

Rounding and grading

  • Factors are decimals to two places (0.82). A factor typed as a percent (82%) is read as 0.82.
  • Amperes are rounded to one decimal place, volts and percents to two, areas to four (square inches).
  • Table lookups and choices must match exactly. Calculated lines are accepted within the tolerance shown beside them, the same amount above or below the key.

Exam practice only. AmpSizer is not affiliated with, endorsed by or connected to any code publisher, testing company or licensing board. A real installation is sized by a licensed electrician to the locally adopted code.