3-1/2-inch Flexible Metal (FMC) Conduit Fill
Wire capacity of trade size 3-1/2 (metric designator 91) Flexible Metal Conduit (FMC), for THHN, XHHW, THW and RHW conductors from 14 AWG to 1000 kcmil.
3-1/2-inch Flexible Metal Conduit holds 76 × #6, 46 × #4, 33 × #2 or 20 × 1/0 AWG THHN conductors at 40% fill. Internal area: 9.621 in²; usable at 40%: 3.848 in².
| Wire size | THHN | XHHW | THW | RHW | THHN in a nipple (60%) | THHN area (in²) |
|---|---|---|---|---|---|---|
| 14 AWG | 396 | 277 | 277 | 131 | 595 | 0.0097 |
| 12 AWG | 289 | 212 | 212 | 109 | 434 | 0.0133 |
| 10 AWG | 182 | 158 | 158 | 88 | 273 | 0.0211 |
| 8 AWG | 105 | 88 | 88 | 46 | 157 | 0.0366 |
| 6 AWG | 76 | 65 | 53 | 37 | 114 | 0.0507 |
| 4 AWG | 46 | 47 | 39 | 29 | 70 | 0.0824 |
| 3 AWG | 39 | 40 | 34 | 25 | 59 | 0.0973 |
| 2 AWG | 33 | 33 | 29 | 22 | 50 | 0.1158 |
| 1 AWG | 24 | 25 | 20 | 14 | 37 | 0.1562 |
| 1/0 AWG | 20 | 21 | 17 | 12 | 31 | 0.1855 |
| 2/0 AWG | 17 | 17 | 14 | 11 | 26 | 0.2223 |
| 3/0 AWG | 14 | 14 | 12 | 9 | 21 | 0.2679 |
| 4/0 AWG | 12 | 12 | 10 | 8 | 18 | 0.3237 |
| 250 kcmil | 9 | 10 | 8 | 6 | 14 | 0.3970 |
| 300 kcmil | 8 | 8 | 7 | 5 | 12 | 0.4608 |
| 350 kcmil | 7 | 7 | 6 | 5 | 11 | 0.5242 |
| 400 kcmil | 6 | 6 | 6 | 4 | 10 | 0.5863 |
| 500 kcmil | 5 | 5 | 5 | 4 | 8 | 0.7073 |
| 600 kcmil | 4 | 4 | 4 | 3 | 6 | 0.8676 |
| 700 kcmil | 4 | 4 | 3 | 3 | 6 | 0.9887 |
| 750 kcmil | 3 | 3 | 3 | 2 | 5 | 1.0496 |
| 800 kcmil | 3 | 3 | 3 | 1 | 5 | 1.1085 |
| 900 kcmil | 3 | 3 | 3 | 1 | 4 | 1.2311 |
| 1000 kcmil | 3 | 3 | 2 | 1 | 4 | 1.3478 |
Mixed wire sizes? Calculate it
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3-1/2-inch conduit: Flexible Metal Conduit vs other types
Trade size is nominal. The real inside diameter, and so the wire count, changes with the wall thickness of each raceway type.
| Conduit type | ID (in) | Area (in²) | 40% (in²) | #12 THHN | #10 THHN | #6 THHN |
|---|---|---|---|---|---|---|
| EMT | 3.834 | 11.545 | 4.618 | 347 | 219 | 91 |
| PVC Schedule 40 | 3.521 | 9.737 | 3.895 | 293 | 184 | 77 |
| PVC Schedule 80 | 3.326 | 8.688 | 3.475 | 261 | 164 | 68 |
| Rigid Metal Conduit | 3.570 | 10.010 | 4.004 | 301 | 189 | 79 |
| IMC | 3.671 | 10.584 | 4.234 | 318 | 200 | 83 |
| Flexible Metal Conduit | 3.500 | 9.621 | 3.848 | 289 | 182 | 76 |
| Liquidtight Flexible Metal Conduit | 3.520 | 9.731 | 3.892 | 292 | 184 | 76 |
Other Flexible Metal Conduit sizes
Frequently asked questions
How many #12 wires fit in 3-1/2-inch Flexible Metal Conduit?
289 conductors of 12 AWG THHN/THWN-2 at the 40% fill limit. With thicker THW or XHHW insulation the count is 212.
What is the inside diameter and area of 3-1/2-inch Flexible Metal Conduit?
The internal diameter is 3.500 in. (88.9 mm) and the total cross-sectional area is 9.621 in². The usable area is 3.848 in² at 40% fill, 2.983 in² for two wires and 5.099 in² for one.
What is the largest wire I can pull three of in 3-1/2-inch Flexible Metal Conduit?
1000 kcmil THHN: 3 conductors fit at 40% fill. That is three current-carrying conductors with no ground; add the ground’s area and check again with the calculator if you need one.
Can I really load it with that many conductors?
For space, yes. But 289 current-carrying conductors in one raceway means heavy ampacity derating — 10 to 20 conductors are adjusted to 50% of their table ampacity. Fill tells you what fits; derating tells you what it can carry.
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