How Many 300 MCM Wires Fit in FMC Conduit?
Complete NEC-compliant fill chart for 300 MCM THHN wires in Flexible Metal Conduit (FMC) conduit. Maximum wire counts for all standard conduit sizes.
Quick Answer
For 300 MCM THHN wires in FMC conduit at 40% fill (3+ wires):
- • 1-1/4" FMC: 1 wires
- • 1-1/2" FMC: 1 wires
- • 2" FMC: 2 wires
300 MCM in FMC Conduit Fill Chart
| Conduit Size | Max Wires (40% Fill) | Fill % | Max Wires (Nipple 60%) | Fill % |
|---|---|---|---|---|
| 1-1/4" | 1 | 34% | 1 | 34% |
| 1-1/2" | 1 | 24% | 2 | 48% |
| 2" | 2 | 29% | 4 | 59% |
| 2-1/2" | 4 | 35% | 6 | 53% |
| 3" | 7 | 40% | 10 | 57% |
| 3-1/2" | 9 | 39% | 13 | 57% |
| 4" | 11 | 38% | 17 | 58% |
Understanding the Fill Chart
According to NEC (National Electrical Code) Chapter 9, Table 1, the maximum conduit fill percentage depends on the number of conductors:
- 1 conductor: 53% fill maximum
- 2 conductors: 31% fill maximum
- 3 or more conductors: 40% fill maximum
- Nipples (24" or less): 60% fill maximum
This chart shows the maximum number of 300 MCM THHN conductors that can fit in each FMC conduit size while maintaining NEC compliance.
Calculation Example
Question: How many 300 MCM THHN wires can fit in 1-1/2" FMC conduit?
Wire area: 0.4608 sq in per conductor
Conduit internal area: 1.901 sq in
Allowable fill (40%): 0.7604 sq in
Maximum wires: 0.7604 ÷ 0.4608 = 1 wires
Answer: You can fit up to 1 wires of 300 MCM THHN in 1-1/2" FMC conduit.