Conduit Fill Calculator
Calculate conduit fill percentage according to NEC standards. Determine how many wires can safely fit in EMT, PVC, RMC, and other conduit types.
Step 1: Conduit Specifications
NEC Conduit Fill Requirements
According to NEC Chapter 9, Table 1, the maximum fill percentage varies:
1 wire: 53%
2 wires: 31%
3+ wires: 40% (most common)
Always check local electrical codes.
Step 2: Wire Configuration
Wire Area Reference
Wire areas based on NEC Chapter 9, Table 5:
14 AWG THHN: 0.0097 in²
12 AWG THHN: 0.0133 in²
10 AWG THHN: 0.0211 in²
8 AWG THHN: 0.0366 in²
6 AWG THHN: 0.0507 in²
Conduit Fill Calculation Results
Conduit Fill Percentage
Interpretation
The conduit fill is 31.2%, which is below the NEC maximum of 40% for 3 or more wires. This configuration is compliant with NEC standards.
Conduit Size Comparison
| Conduit Size | Type | Area (in²) | Current Fill | Status | Max Wires* |
|---|
* Maximum number of 12 AWG THHN wires at 40% fill
NEC Conduit Fill Standards
Maximum Fill Percentages
According to NEC Chapter 9, Table 1:
1 wire: 53% of conduit cross-section
2 wires: 31% of conduit cross-section
3 or more wires: 40% of conduit cross-section
Note: Different percentages apply for cable and flexible conduit.
Calculation Formula
Fill Percentage = (Total Wire Area / Conduit Internal Area) × 100
Total Wire Area = Σ(Wire Area × Number of Wires)
Wire areas are specified in NEC Chapter 9, Table 5 for various insulation types.
Derating Factors
When conduit contains 4 or more current-carrying conductors, additional derating factors apply per NEC 310.15(B)(3)(a). These affect ampacity but not physical fill calculations.
Important Notes
1. Always consult the latest NEC code and local amendments
2. Grounding conductors are counted in fill calculations
3. Different wire insulations have different area allowances
4. Conduit fill calculations do not account for wire bending radius
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