WireGaugeCalc Free calculator · NEC cited · works offline
Calculating Ampacity For Motors
Calculating ampacity for motors is fast with WireGaugeCalc, since you enter the motor full-load current and it returns the required conductor ampacity.
It applies the 125% sizing factor for a continuous motor load and reads the matching gauge from the termination temperature column, so the conductor will not overheat.
You get the sized conductor in seconds, so the branch circuit holds the motor without nuisance trips.
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 motor full-load current drives the ampacity
Branch-circuit conductors for a single motor are sized at 125% of the motor full-load current, so the tool scales the FLA before reading the table.
It uses the termination temperature column your starter and breaker are listed for, since the 90C value cannot be used at 75C lugs.
Inputs for sizing motor branch-circuit conductors
The calculator uses these to size the run:
- Motor full-load current in amps
- Continuous duty so the 125% factor applies
- Copper or aluminum conductor
- Termination temperature: 60C, 75C, or 90C
- One-way run length for voltage drop
One app for every NEC calculation
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
Do I use nameplate amps or table FLC when calculating motor ampacity?
Conductor sizing uses the full-load current from the NEC motor tables, not the nameplate amps, while overload protection uses the nameplate. The tool applies 125% to the table value for branch-circuit conductors.
Does the conductor get sized the same as the overcurrent device for a motor?
No, motor branch-circuit protection is often sized well above the conductor ampacity to allow inrush. Confirm both the conductor and device values 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.