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Technical Reference
Reference data and NEC citations for EMT, IMC, RMC, and PVC conduit types used in the calculator, including terminology like raceway fill, conductor volume, wire capacity, and derating factors.
EMT is a thin-wall steel raceway commonly used indoors in dry locations. NEC Article 358 covers EMT installation and usage. EMT is favored for ease of bending and cost-effective physical protection.
| Trade Size | Internal Area | Max Fill (40%) |
|---|---|---|
| 1/2" | 0.304 | 0.1216 |
| 3/4" | 0.533 | 0.2132 |
| 1" | 0.864 | 0.3456 |
| 1-1/4" | 1.496 | 0.5984 |
| 1-1/2" | 2.036 | 0.8144 |
| 2" | 3.356 | 1.3424 |
| 2-1/2" | 5.858 | 2.3432 |
| 3" | 8.846 | 3.5384 |
| 3-1/2" | 11.545 | 4.6180 |
| 4" | 15.003 | 6.0012 |
IMC is a lighter-weight steel raceway than RMC while still providing strong physical protection. NEC Article 342 governs IMC construction and installation, including threaded fittings and corrosion-resistant finishes.
RMC is a heavy-wall, threaded steel raceway that provides strong physical damage protection. NEC Article 344 addresses RMC requirements, including threaded fittings and galvanized or corrosion-resistant finishes for durability in demanding environments.
PVC is corrosion resistant and commonly used underground. NEC Article 352 covers PVC conduit, including Schedule 40 and Schedule 80 wall thickness requirements. Schedule 80 provides greater physical protection. Account for thermal expansion and contraction in long runs, especially in outdoor installations.
NEC Chapter 9, Table 1 specifies maximum conduit fill percentages based on the number of conductors: 53% for one conductor, 31% for two conductors, and 40% for more than two conductors. These limits protect against overheating and ensure safe pulling conditions.
Jamming can occur when three conductors approach certain size ratios, increasing sidewall pressure during pulls. Following NEC Chapter 9, Table 4 conduit areas and applying the fill limits helps prevent jamming and protects conductor insulation.
Representative conductor areas used in the calculator. Always verify exact values in NEC Chapter 9 tables for your specific insulation type and manufacturer data.
| AWG | THHN Area | THWN Area |
|---|---|---|
| 14 | 0.0097 sq in | 0.0097 sq in |
| 12 | 0.0133 sq in | 0.0133 sq in |
| 10 | 0.0211 sq in | 0.0211 sq in |
| 8 | 0.0366 sq in | 0.0366 sq in |
| 6 | 0.0507 sq in | 0.0507 sq in |
Reference content aligned to the latest NEC cycle for current best practices.
Intended for electricians and engineers. Always verify with your local AHJ (Authority Having Jurisdiction) and project specifications.
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The National Electrical Code (NEC) requires that conduits not be filled beyond certain percentages to ensure proper heat dissipation and easy wire pulling. Our calculator ensures compliance with these critical safety requirements.
Our calculator uses official NEC Chapter 9 data and Annex C tables to ensure 100% accurate results. Trusted by electricians, engineers, and contractors worldwide for critical electrical installations.