Fill limits
| Internal area | 0.887 in² |
|---|---|
| One conductor | 53% — 0.4701 in² |
| Two conductors | 31% — 0.2750 in² |
| More than two | 40% — 0.3548 in² |
Reference tables · Conduit fill
RMC (rigid metal conduit)
1" RMC conduit fill capacity
1" RMC has an internal area of 0.887 in². At the 40% limit that applies to more than two conductors, it holds up to 26 12 AWG THHN conductors.
Capacity
Maximum conductors by size and insulation
| Conductor | THHN / THWN-2 | XHHW-2 | THW |
|---|---|---|---|
| 14 AWG | 36 | 25 | 16 |
| 12 AWG | 26 | 19 | 13 |
| 10 AWG | 16 | 14 | 10 |
| 8 AWG | 9 | 8 | 6 |
| 6 AWG | 6 | 6 | 4 |
| 4 AWG | 4 | 4 | 3 |
| 3 AWG | 3 | 3 | 3 |
| 2 AWG | 3 | 3 | 2 |
| 1 AWG | 1 | 1 | 1 |
| 1/0 AWG | 1 | 1 | 1 |
| 2/0 AWG | 1 | 1 | 1 |
| 3/0 AWG | 1 | 1 | 1 |
| 4/0 AWG | 1 | 1 | 1 |
| 250 kcmil | 1 | 1 | 1 |
| 300 kcmil | 1 | 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
Related