Fill limits
| Internal area | 7.499 in² |
|---|---|
| One conductor | 53% — 3.9745 in² |
| Two conductors | 31% — 2.3247 in² |
| More than two | 40% — 2.9996 in² |
Reference tables · Conduit fill
RMC (rigid metal conduit)
3" RMC conduit fill capacity
3" RMC has an internal area of 7.499 in². At the 40% limit that applies to more than two conductors, it holds up to 225 12 AWG THHN conductors.
Capacity
Maximum conductors by size and insulation
| Conductor | THHN / THWN-2 | XHHW-2 | THW |
|---|---|---|---|
| 14 AWG | 309 | 215 | 143 |
| 12 AWG | 225 | 165 | 115 |
| 10 AWG | 142 | 123 | 90 |
| 8 AWG | 81 | 68 | 53 |
| 6 AWG | 59 | 50 | 41 |
| 4 AWG | 36 | 36 | 30 |
| 3 AWG | 30 | 31 | 26 |
| 2 AWG | 25 | 26 | 22 |
| 1 AWG | 19 | 19 | 15 |
| 1/0 AWG | 16 | 16 | 13 |
| 2/0 AWG | 13 | 13 | 11 |
| 3/0 AWG | 11 | 11 | 9 |
| 4/0 AWG | 9 | 9 | 8 |
| 250 kcmil | 7 | 7 | 6 |
| 300 kcmil | 6 | 6 | 5 |
| 350 kcmil | 5 | 5 | 5 |
| 400 kcmil | 5 | 5 | 4 |
| 500 kcmil | 4 | 4 | 3 |
| 600 kcmil | 3 | 3 | 3 |
| 700 kcmil | 3 | 3 | 2 |
| 750 kcmil | 2 | 2 | 1 |
Fitting is not the same as finishing
These counts are the mathematical fill limit, not a promise the pull will go well. A raceway at 39% fill with four 90° bends and a hundred feet between pull points is legal and miserable. Experienced installers routinely size up a trade size on long or bendy runs, and the material cost difference is usually smaller than the labour cost of a fight.
Two other things this table does not model. Nipples 24 inches and shorter between enclosures are permitted a much higher fill. And a mixed set of conductor sizes has to be summed by area rather than looked up by count — the conduit fill calculator handles that.
Remember also that conductor count drives ampacity derating separately. Filling this conduit with current-carrying conductors will reduce what each one can carry — see the bundling adjustment table.
Source: NFPA 70, National Electrical Code, Chapter 9, Table 1; NFPA 70, National Electrical Code, Chapter 9, Table 4; NFPA 70, National Electrical Code, Chapter 9, Table 5. Published by NFPA.NEC 2023
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