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NEC Art.250
Validated against the standard.
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$2.99 Pro
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How it works
Enter your values
Type in your inputs — the app fills code tables and constants for you, so there's nothing to look up.
Get a code-checked result
Instant answer with a clear PASS / FAIL and the exact NEC Art.250 reference behind every number.
Save & export
Keep a history of calculations and export a clean PDF report to share or attach to a permit (Pro).
What this calculator does
Grounding has three different conductors, each sized from a different table, and mixing them up is a common mistake. This app sizes the equipment grounding conductor (EGC), the grounding electrode conductor (GEC), and bonding jumpers using the correct NEC table for each.
Which table for which conductor
- EGC — Table 250.122, sized by the rating of the overcurrent device protecting the circuit.
- GEC — Table 250.66, sized by the largest ungrounded service-entrance conductor.
- Bonding jumpers — 250.102, on the supply side sized like the GEC, on the load side like the EGC.
Worked examples
EGC: a circuit protected at 100 A → Table 250.122 gives #8 copper (or #6 aluminum).
GEC: a service with 2 AWG copper ungrounded conductors → Table 250.66 gives #8 copper. (To a ground rod, 250.66(A) never requires larger than #6 copper.)
The app also applies 250.122(B): when you upsize the circuit conductors — for example for voltage drop — the EGC has to be increased proportionally.
Related calculators
Use it with the wire size calculator for the phase conductors and the breaker size calculator for the device that sets the EGC.
Grounding size FAQ
What is the difference between the EGC and the GEC?
The equipment grounding conductor (EGC) bonds equipment back to the source and is sized by the overcurrent device using Table 250.122. The grounding electrode conductor (GEC) connects the system to the earth electrodes and is sized by the service conductors using Table 250.66.
Do I upsize the EGC when I upsize the phase conductors?
Yes. NEC 250.122(B) requires the EGC to be increased in proportion to the circular-mil increase of the ungrounded conductors whenever they are upsized, such as for voltage drop.
Is there a maximum size for the GEC to a ground rod?
Yes. Under 250.66(A), the GEC to a made electrode such as a ground rod is never required to be larger than #6 copper.
Copper and aluminum?
Both. The calculator gives the copper and aluminum selections from each table so you can use whichever the installation calls for.
Does it work offline?
Yes, it runs 100% offline with no account. Free with rewarded ads; a one-time $2.99 Pro unlock adds PDF export and saved history.
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