Ampacity Calculator
Determine allowable conductor current-carrying capacity with full temperature correction factors, raceway bundling derating, and equipment terminal limitations.
Conductor & Cable Selection
Allowable Conductor Ampacity
Code-compliant current capacity with temperature & bundling derates
95 A 90°C Column
Base Table Ampacity 95 A
Ambient Temp Factor 1.00 (78-86°F)
Bundling Derate 1.00 (100%)
Total Run Capacity 95 A (1 Run)
Conductor Ampacity Derating Engine
Conductor insulation degrades under elevated ambient temperatures and heat trapped within bundled conduits. NEC 310.15 mandates applying compound correction factors to base ampacities to maintain electrical safety.
Formula:
I_adjusted = I_base(310.16) × Factor_temp × Factor_bundling | I_final ≤ I_terminal(60°C / 75°C) Variables & Parameters
I_adj Adjusted allowable conductor ampacity
I_base Base ampacity from NEC Table 310.16
F_temp Ambient temperature correction multiplier (NEC 310.15(B)(1))
F_bundle More than 3 current-carrying conductors adjustment multiplier
Frequently Asked Questions
How do you calculate ampacity?
To calculate derated conductor ampacity per NEC 310.15: Start with the baseline ampacity from NEC Table 310.16 for your conductor material, gauge, and insulation temperature rating (60°C, 75°C, or 90°C). Multiply by the Ambient Temperature Correction Factor (Table 310.15(B)(1)) and the Conductor Bundling Adjustment Factor (Table 310.15(C)(1) if more than 3 current-carrying conductors share a raceway). Verify the adjusted ampacity meets equipment termination temperature ratings (NEC 110.14(C)).
How do you calculate derated ampacity for conductors and cables?
A wire ampacity calculator or cable ampacity calculator multiplies the base ampacity from NEC Table 310.16 by the Ambient Temperature Correction Factor (NEC 310.15(B)(1)) and the Conductor Bundling Adjustment Factor (NEC 310.15(C)(1)). The final current cannot exceed the equipment terminal rating (NEC 110.14(C)).
How does this compare to the Southwire ampacity calculator and Cerrowire tool?
This conductor ampacity calculator incorporates full NEC Table 310.16 ratings across copper and aluminum conductors (THHN, XHHW, USE-2, NM-B, MC Cable), providing exact temperature and raceway bundling deratings matching Southwire ampacity calculator and Cerrowire ampacity charts.
What is the NEC 110.14(C) terminal temperature limitation?
Standard circuit breakers and equipment rated 100A or less are rated for 60°C or 75°C terminations. Even if using 90°C wire (like THHN), the final ampacity is capped at the 75°C column of Table 310.16, though 90°C ratings can be used as the starting point for derating.