How many 250 kcmil THHN fit in 2-1/2" Rigid?
5250 kcmil THHN/THWN-2 wires in 2-1/2" Rigid metal conduit (RMC, GRC)
4.866 sq in × 40 % = 1.9464 sq in allowed. ÷ 0.3970 sq in per wire = 4.90, which Note 7 rounds up to 5 because the decimal is 0.8 or more.
This pull in numbers
- 5 wires fill
- 40.8 % of 2-1/2" Rigid
- Limit for three or more
- 40 %
- For 6 or more
- 3" Rigid, up to 7
- Pipe to wire diameter
- 3.50 to 1
- In THW insulation
- 4 fit
- In XHHW-2 insulation
- 5 fit
Before you pull 5
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 5 is the total, not the hots.
- Derating. If all 5 were current-carrying, each would be adjusted to 80 % of its ampacity (Table 310.15(C)(1)): a 250 kcmil THHN at 290 A in the 90 °C column becomes 232 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.
250 kcmil THHN in other 2-1/2" conduit
| Conduit | Inside area | Most 250 kcmil THHN |
|---|---|---|
| Electrical metallic tubing | 5.858 | 6 |
| Intermediate metal conduit | 5.135 | 5 |
| Rigid metal conduit (RMC, GRC) | 4.866 | 5 |
| Rigid PVC conduit, Schedule 40 | 4.695 | 4 |
| Rigid PVC conduit, Schedule 80 | 4.119 | 4 |
| Flexible metal conduit (FMC, Greenfield) | 4.909 | 5 |
| Liquidtight flexible metal conduit (LFMC) | 4.881 | 5 |
250 kcmil THHN in other Rigid sizes
Other wire sizes in 2-1/2" Rigid
#14: 200#12: 146#10: 92#8: 53#6: 38#4: 23#3: 20#2: 17#1: 12#1/0: 10#2/0: 8#3/0: 7#4/0: 6250 kcmil: 5300 kcmil: 4350 kcmil: 3500 kcmil: 2