WireGaugeCalc Free calculator · NEC cited · works offline
14 THHN Ampacity
14 thhn ampacity is simple with WireGaugeCalc, since you pick the temperature column and material and it returns the rated value.
It reads the 14 AWG THHN figure from NEC 310.16 and shows each termination temperature column, so you apply the rating your equipment allows.
You get the usable ampacity in seconds, so you protect the conductor at the correct breaker size.
Open the calculatorAllowable ampacity from NEC Table 310.16 at the chosen termination temperature. Field aid only, verify against the current NEC and your local authority having jurisdiction.
How the 14 AWG THHN rating is read
THHN is a 90C insulation, so the table lists a higher 90C value, but the usable rating drops to the column your lugs are listed for.
Small conductors fall under the protection note, so the 14 AWG copper breaker is limited even when the 90C ampacity looks higher.
What the 14 THHN ampacity result depends on
These inputs set the value returned:
- Termination temperature: 60C, 75C, or 90C column
- Copper THHN versus aluminum
- Ambient temperature for correction
- Number of current-carrying conductors for adjustment
- Whether the small-conductor protection limit applies
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WireGaugeCalc keeps the calculations you reach for most in one place:
- Voltage drop and wire sizing for any run
- Conduit fill for EMT, PVC, and RMC
- Box fill and junction box sizing
- Ampacity and temperature derating
- Motor circuit and load calculations
- Conduit bend offsets and saddles
Built for the field, works offline
The whole app runs on your phone, so it keeps working in a basement, an attic, or a job site with no signal.
There is no account to create and nothing to load. Open it, run the number, and get back to work.
- No signup and no signal needed
- Answers in a tap, not a spreadsheet
- Same tool on phone, tablet, and desktop
Every result cites the NEC article
Each answer shows the table or formula it came from, so you can check the method and learn the code as you go.
That makes the app useful on the job and during exam prep, since the reasoning is right next to the number.
Switch the code year your job runs on
Jurisdictions adopt the NEC at different times, so you can match the calculation to the code in force:
- NEC 2017, 2020, and 2023 tables
- Copper and aluminum conductors
- 60, 75, and 90 degree C terminations
- Single-phase and three-phase systems
Run the number, then get back to work
Stop flipping through a paper book or hopping between calculator sites. Enter your values, read the code-cited answer, and move on. Free to use, no signup.
Open the calculatorFrequently asked questions
Why is 14 AWG copper limited to a 15A breaker if the 90C ampacity is higher?
The small-conductor rule caps the overcurrent protection for 14 AWG copper at 15A regardless of the higher 90C insulation value. The 90C column is mainly used as a starting point for derating, not for final protection.
Can I use the 90C THHN value if the wire ends at 75C lugs?
No, you must drop to the 75C column for the final rating since the termination is the weakest link. Verify the column and the small-conductor limit against the current NEC and your local authority having jurisdiction.
Is WireGaugeCalc free to use?
Yes. Every calculator is free to run with no signup. A paid tier adds saved projects, PDF reports, and extra code years, but the core math stays free.
Does it work without internet?
Yes. The app runs on your device, so it keeps working with no signal on a job site, in a basement, or in an attic.
Are the results code accurate?
Results follow published NEC tables and standard formulas, and each answer shows the article it came from. It is a field aid, not a stamp of approval, so verify against the current code and your local authority before you wire anything.
Which NEC code year does it use?
You can switch between NEC 2017, 2020, and 2023, since jurisdictions adopt the code at different times. Pick the year your job runs on.