Cable Ampacity Calculator
Determine cable ampacity with NEC derating factors for temperature, conduit fill, and continuous loads.
Inputs
AWG
(1=THHN, 2=XHHW)
°C
conductors
(0=no, 1=yes)
Results
Derated Ampacity
40 A
Required Breaker Size
40 A
Base Ampacity40 A
Maximum Allowable Load32 A
How to Use This Calculator
- Select the Conductor Size in AWG — smaller AWG numbers indicate larger wires (e.g., AWG 10 is larger than AWG 14).
- Select the Insulation Type: THHN is the most common general-purpose wire; XHHW is used in wet locations.
- Enter the Ambient Temperature in °C around the conductors — NEC base is 30°C; higher temperatures require derating.
- Enter the number of Current-Carrying Conductors in the raceway — three or fewer requires no fill derating.
- Indicate whether this is a Continuous Load (3+ hours) — NEC requires conductors to be derated to 80% for continuous loads.
- Read the Derated Ampacity in amperes and the Required Breaker Size to confirm the circuit is properly protected.
Ad Placeholder
Related Calculators
Conduit Fill Calculator
Check NEC conduit fill compliance: calculate fill percentage, compare to code limits, and find maximum conductor count.
Voltage Regulation Calculator
Calculate voltage drop, drop percentage, and receiving-end voltage for power cables with resistance and reactance.
Motor Starting Current Calculator
Calculate motor full load amps, starting inrush current, voltage drop during starting, and starting KVA demand.
Ad Placeholder