WireGaugeCalc Free calculator · NEC cited · works offline
250 Amp Service Wire Size
250 amp service wire size is simple with WireGaugeCalc, since you set the service rating and conductor material and read the gauge.
It applies the NEC ampacity tables and the 75 degree C termination column used on most service equipment.
You get the copper and aluminum options together, so the service entrance is sized right the first time.
Open the calculatorSmallest conductor whose ampacity meets the load, NEC Table 310.16. Field aid only, verify against the current NEC and your local authority having jurisdiction.
Picking The Service Conductor For 250 Amps
A 250 amp service typically needs 250 kcmil copper or 350 kcmil aluminum at the 75 degree C column.
Service conductors are sized to carry the full service rating, so the ampacity must meet or exceed 250 amps.
Long runs may need upsizing for voltage drop, and the neutral and grounding electrode conductor are sized separately.
How WireGaugeCalc Sizes The Service Wire
Give the tool a few details and it returns the conductor size:
- Service rating set to 250 amps
- Copper or aluminum conductor
- 75 degree C termination column
- NEC ampacity table value
- Separate notes for neutral and grounding electrode conductor
- Voltage-drop upsizing for long runs
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 copper or aluminum do I need for a 250 amp service?
At the 75 degree C column a 250 amp service usually takes 250 kcmil copper or 350 kcmil aluminum. Long runs may push you a size larger for voltage drop.
Is the neutral the same size as the hot conductors on a 250 amp service?
Not always. The grounded conductor is sized for the unbalanced load and the minimum grounding rules, so it can be smaller. Verify all conductor sizes 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.