How Many 4/0 AWG Wires Fit in RMC Conduit?
Complete NEC-compliant fill chart for 4/0 AWG THHN wires in Rigid Metal Conduit (RMC) conduit. Maximum wire counts for all standard conduit sizes.
Quick Answer
For 4/0 AWG THHN wires in RMC conduit at 40% fill (3+ wires):
- • 1-1/4" RMC: 1 wires
- • 1-1/2" RMC: 2 wires
- • 2" RMC: 3 wires
4/0 AWG in RMC Conduit Fill Chart
| Conduit Size | Max Wires (40% Fill) | Fill % | Max Wires (Nipple 60%) | Fill % |
|---|---|---|---|---|
| 1-1/4" | 1 | 24% | 2 | 49% |
| 1-1/2" | 2 | 36% | 3 | 54% |
| 2" | 3 | 33% | 5 | 54% |
| 2-1/2" | 6 | 37% | 9 | 55% |
| 3" | 9 | 37% | 14 | 58% |
| 3-1/2" | 12 | 38% | 18 | 57% |
| 4" | 16 | 40% | 24 | 60% |
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 4/0 AWG THHN conductors that can fit in each RMC conduit size while maintaining NEC compliance.
Calculation Example
Question: How many 4/0 AWG THHN wires can fit in 1-1/2" RMC conduit?
Wire area: 0.3701 sq in per conductor
Conduit internal area: 2.071 sq in
Allowable fill (40%): 0.8284 sq in
Maximum wires: 0.8284 ÷ 0.3701 = 2 wires
Answer: You can fit up to 2 wires of 4/0 AWG THHN in 1-1/2" RMC conduit.