WireGaugeCalc Free calculator · NEC cited · works offline
NEC Sizing Motro Power Cables
NEC sizing motro power cables is straightforward with WireGaugeCalc, which sizes motor conductors from the full load current.
You enter the motor horsepower, voltage, and phase, so the tool finds the table FLA and applies the 125 percent factor.
That gives you a conductor size you can trust before pulling cable to the motor.
Open the calculatorEnter any two values and read the rest.
Ohm’s law: V = I × R and P = V × I. Field aid only, verify against the current NEC and your local authority having jurisdiction.
The 125 Percent Rule For Motor Conductors
NEC 430.22 requires single-motor branch-circuit conductors to carry at least 125 percent of the motor full load current, since the motor runs continuously.
The full load current comes from NEC Table 430.250 for three-phase motors, not the nameplate, so the calculator uses the table value to apply the factor.
Because the conductor is sized above the running current, the wire stays within ampacity even under steady load.
What Goes Into Sizing The Motor Power Cables
Enter the motor and the tool returns the cable size:
- Motor horsepower and supply voltage
- Single-phase or three-phase selection
- Table full load amps from NEC 430.250
- The 125 percent branch-circuit conductor factor
- Copper or aluminum conductor at the chosen temperature column
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
Why are motor cables sized at 125 percent of FLA?
A motor is a continuous load under the NEC, so 430.22 has the branch-circuit conductors carry 125 percent of the full load current. This keeps the wire below its ampacity during steady running.
Do I use the nameplate amps or the table FLA to size the cables?
Use the table full load current from NEC 430.250 for conductor sizing, and use the nameplate amps only for the overload device. Verify your sizing against the current NEC and the 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.