WireGaugeCalc Free calculator · NEC cited · works offline
Ground Wire Size For 400 Amp Service
ground wire size for 400 amp service is fast with WireGaugeCalc, since you enter the service rating and conductor material and the tool returns the grounding conductor size.
You pick copper or aluminum, and the calculator reads the matching NEC grounding table so the result fits the service ahead of it.
The payoff is a grounding conductor size you can confirm with the right table before you pull the wire.
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.
Why The 400 Amp Service Sets The Ground Wire Size
The grounding electrode conductor is sized from the largest ungrounded service conductor, so a 400 amp service drives a larger ground than a small panel.
Copper and aluminum carry differently, so the calculator keeps the material separate and returns the size that matches your run.
What The Ground Wire Size 400 Amp Service Tool Checks
WireGaugeCalc looks at the inputs that change the grounding conductor for a 400 amp service:
- Service rating in amps
- Conductor material, copper or aluminum
- Grounding electrode conductor size per NEC 250.66
- Equipment grounding conductor size per NEC 250.122
- Service entrance conductor size feeding the result
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 grounding electrode conductor does a 400 amp service need?
A 400 amp service lands on a larger grounding electrode conductor than smaller services because it is sized from the service conductor. Confirm the exact AWG against the current NEC 250.66 table and your local authority having jurisdiction before you cut wire.
Is the equipment grounding conductor the same size as the grounding electrode conductor?
No, the equipment grounding conductor is sized from NEC 250.122 by overcurrent device, while the grounding electrode conductor uses NEC 250.66. They are different tables, so the tool returns each one separately.
Can I use aluminum for the ground wire on a 400 amp service?
Aluminum is allowed where listed for the location, and it lands on a larger size than copper since it carries less per AWG. The calculator switches the size when you change the material.
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.