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Conduit fill practice

Conductor areas, the total, the permitted fill and the smallest trade size that takes them.

Conduit fill with mixed conductors

Problem

Problem code FILL-001J0Y

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 run of EMT (electrical metallic tubing) will carry 2 × 8 AWG and 1 × 12 AWG THHN / THWN-2 conductors, 3 conductors in all. Find the total conductor area and the smallest EMT trade size that holds them within the permitted fill.

Raceway
EMT (electrical metallic tubing)
Insulation
THHN / THWN-2
8 AWG
2
12 AWG
1
  1. in²

    Within ±0.00005 in²

  2. in²

    Within ±0.00005 in²

  3. in²

    Within ±0.0005 in²

  4. %

    Must match

  5. Must match

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

Check the numbers in the conduit fill 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

  • Areas are the approximate insulated-conductor areas for the stated insulation; the sizes are mixed, so the area method applies rather than a same-size fill table.
  • More than two conductors fill to 40%. Nipples, compact conductors and cables are not modelled.

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.