Cable Sizing Calculator per NEC (NFPA 70) for Industrial Installations
Conductor sizing for NEC 2026 industrial installations follows Article 430 for motor branch circuits — sizing conductors at 125% of motor FLC from Table 430.248/250, applying Table 310.16 ampacities with Article 310.15(C) adjustment factors for cable tray runs, and coordinating overcurrent protection per Article 430.52 for motor short-circuit and ground-fault protection.
Quick Reference Table
| NEC 2026 Industrial Conductor Sizing References — NEC (NFPA 70) (2026 Edition) | ||
|---|---|---|
| Parameter | Value / Requirement | Clause Reference |
| Motor FLC tables | Full-load current for single and three-phase motors | Table 430.248 / Table 430.250 |
| Motor conductor sizing | 125% of FLC for continuous duty motors | Article 430.22 |
| Motor SCGF protection | Maximum device ratings by type | Article 430.52, Table 430.52 |
| Cable tray ampacities | Ampacity for conductors in cable tray | Article 392.80 |
| High ambient correction | Correction for process area temperatures | Table 310.15(B)(1) |
| Short circuit protection | Conductor damage curves and device coordination | Article 240.1, Informational Note No. 2 |
How to Calculate Cable Sizing for Industrial Installations
- 1
Determine motor full-load current
Use Table 430.248 (single-phase) or Table 430.250 (three-phase) for the motor FLC — always use the table value, never the motor nameplate, per Article 430.6(A)(1).
- 2
Size the motor branch circuit conductors
Per Article 430.22, size conductors at not less than 125% of the motor FLC from the appropriate table. For example, a 50 hp, 460 V motor has a table FLC of 65 A, requiring conductors rated for at least 81.25 A.
- 3
Apply adjustment and correction factors
Apply Article 310.15(C) adjustment for conduit fill and Table 310.15(B)(1) temperature correction. Industrial environments near furnaces or boilers may require correction for 40-50 °C ambient.
- 4
Select the motor short-circuit protection
Per Table 430.52, select the short-circuit and ground-fault protective device — for inverse-time breakers, maximum 250% of motor FLC. Size conductors to withstand the let-through energy of this device.
- 5
Verify voltage drop for long motor feeders
Calculate voltage drop at full-load current. For motor circuits, also check that starting voltage at motor terminals (typically 6x FLC for DOL start) stays above the motor minimum starting voltage.
- 6
Size the equipment grounding conductor
Select the equipment grounding conductor from Table 250.122 based on the rating of the overcurrent device protecting the circuit. For parallel conductors, size each EGC per the full-size overcurrent device.
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Calculate Cable Sizing NowNEC vs IEC 60364 Cable Sizing Comparison
| Parameter | NEC | IEC 60364 |
|---|---|---|
| Conductor sizing unit | AWG/kcmil | mm² |
| Voltage drop recommendation | 3% branch / 5% total | 4% lighting / 5% other |
| Reference ambient temp | 30°C | 30°C (air), 20°C (ground) |
| Continuous load multiplier | 1.25x required | Not explicitly required |
| Ampacity table | Table 310.16 (60/75/90°C) | Tables B.52.2–B.52.13 |
| Conduit fill limit | 40% for 3+ conductors | Not specified (derating instead) |