How many #1 THHN fit in 4" IMC?
351 AWG THHN/THWN-2 wires in 4" Intermediate metal conduit
13.631 sq in × 40 % = 5.4524 sq in allowed. ÷ 0.1562 sq in per wire = 34.91, which Note 7 rounds up to 35 because the decimal is 0.8 or more.
This pull in numbers
- 35 wires fill
- 40.1 % of 4" IMC
- Limit for three or more
- 40 %
- For 36 or more
- no bigger IMC
- Pipe to wire diameter
- 9.34 to 1
- In THW insulation
- 28 fit
- In XHHW-2 insulation
- 35 fit
Before you pull 35
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 35 is the total, not the hots.
- Derating. If all 35 were current-carrying, each would be adjusted to 40 % of its ampacity (Table 310.15(C)(1)): a #1 THHN at 145 A in the 90 °C column becomes 58 A. Grounds don't count as current-carrying. How derating works
- Bends. A full pipe pulls hard. Keep to 360° of bends between pull points, less for a tight fill.
#1 THHN in other 4" conduit
| Conduit | Inside area | Most #1 THHN |
|---|---|---|
| Electrical metallic tubing | 14.753 | 37 |
| Intermediate metal conduit | 13.631 | 35 |
| Rigid metal conduit (RMC, GRC) | 12.882 | 33 |
| Rigid PVC conduit, Schedule 40 | 12.554 | 32 |
| Rigid PVC conduit, Schedule 80 | 11.258 | 29 |
| Flexible metal conduit (FMC, Greenfield) | 12.566 | 32 |
| Liquidtight flexible metal conduit (LFMC) | 12.692 | 32 |
#1 THHN in other IMC sizes
Other wire sizes in 4" IMC
#8: 149#6: 107#4: 66#3: 56#2: 47#1: 35#1/0: 29#2/0: 24#3/0: 20#4/0: 17250 kcmil: 13300 kcmil: 12350 kcmil: 10500 kcmil: 7