Conduit and Tubing Fill
Chapter 9 Tables 1, 4, 5 and 8 and the Nipple Rule
NFPA 70 National Electrical Code, 2023 edition · Reviewed 2026-09-21
Conduit fill is the calculation the Wiring Methods and Materials topic is built around, on both the Class I and Class II exams. The Georgia exam is open book, so the skill is knowing which table, which column, and which rounding rule — fast. Written from the 2023 text of Chapter 9 (the tables did not change between the 2020, 2023 and 2026 editions).
1. The rule — Table 1
Table 1 — maximum percent of the raceway's cross-sectional area that conductors and cables may occupy:
| Number of conductors and/or cables | Fill |
|---|---|
| 1 | 53% |
| 2 | 31% |
| Over 2 | 40% |
Why 31% for two? Two round conductors side by side waste the space between them — the code is deliberately conservative there.
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