WireGaugeCalc Free calculator · NEC cited · works offline
Ground Size For 125 Amp Service
ground size for 125 amp service is fast with WireGaugeCalc, since you enter the service rating and material and the app reads the grounding tables.
It separates the grounding electrode conductor from the equipment grounding conductor, as the NEC sizes them from different tables.
You get both sizes so you can finish the service ground without guesswork.
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.
Sizing The Grounding Conductors
The grounding electrode conductor is sized from NEC Table 250.66 using the largest service conductor, so a 125 amp copper service often lands at 8 AWG copper.
When the electrode is a rod, 6 AWG copper is the largest that the code requires for that connection.
The equipment grounding conductor comes from Table 250.122 by the overcurrent rating, which is 6 AWG copper at 125 amps.
What Sets The Ground Size
The grounding sizes depend on a few inputs:
- Service rating, here 125 amps
- Largest ungrounded service conductor size
- Copper or aluminum grounding conductor
- Electrode type, rod versus water pipe
- Table 250.66 for the GEC, Table 250.122 for the EGC
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 ground wire do I run to a ground rod on a 125 amp service?
A connection to a single ground rod never needs larger than 6 AWG copper, since the rod limits the required conductor. Always verify the connection and rod count against the current NEC and your local authority having jurisdiction.
Is the grounding electrode conductor the same as the equipment ground?
No, they are sized from different tables. The grounding electrode conductor uses Table 250.66 from the service conductor, while the equipment grounding conductor uses Table 250.122 from the breaker rating.
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.