WireGaugeCalc Free calculator · NEC cited · works offline
400 Amps Through Wire
400 amps through wire is fast to check with WireGaugeCalc, since you enter the amperage and it returns the conductor the NEC ampacity tables allow.
The calculator reads NEC 310.16, so it matches each result to the copper or aluminum size and the termination temperature column you choose.
You see the required conductor in seconds, so you can size a 400 amp feed without flipping through tables by hand.
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.
400 Amp Service What Size Wire Needs
A single conductor rarely carries 400 amps, so the calculator shows the sizes and parallel sets that reach that ampacity.
Picking 400 amp service what size wire to run depends on copper versus aluminum, since each metal carries a different rating at the same gauge.
The tool ties every answer to the 75 degree C column most lugs use, so the rating you read matches the terminations on the panel.
How WireGaugeCalc Sizes a 400 Amp Feed
The calculator works through the same steps an inspector checks:
- Reads ampacity from NEC 310.16 for the conductor you select
- Switches between copper and aluminum at the same amperage
- Holds to the 75 degree C termination column by default
- Shows parallel conductor sets when a single run falls short
- Flags where a larger gauge is needed for the 400 amp target
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
What size wire carries 400 amps?
No common single conductor reaches 400 amps at 75 degrees C, so the load is usually split across parallel sets such as two runs of 600 kcmil copper. Confirm the exact size against the current NEC and your local authority having jurisdiction before you order conductors.
Can I use aluminum for a 400 amp service?
Yes, aluminum is common on large feeders, but it needs a larger gauge than copper for the same 400 amps. The calculator shows both metals so you can compare them side by side.
Why does the termination temperature matter at 400 amps?
Lugs and breakers are usually rated for 75 degrees C, so you must size to that column even when the conductor insulation is rated higher. Sizing to a hotter column than the terminations allow is not permitted.
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.