Ground Wire Size Calculator | NEC 250.66 & 250.122
Free online tool • NEC Table 250.66 (GEC) and Table 250.122 (EGC) • 2026 NEC
Use this free ground wire size calculator to determine the minimum grounding conductor size for branch circuits and feeder equipment grounding (EGC) or service entrance grounding electrode conductors (GEC). Covers both copper and aluminum conductors per the 2026 National Electrical Code.
Select the rating of the circuit breaker or fuse protecting this branch circuit or feeder.
Minimum Required Size
NEC Table 250.122copper · Equipment Grounding Conductor (EGC)
NEC Table 250.122 Reference Table (Copper)
| OCD Rating | Min Copper Size |
|---|---|
| 15 A | 14 AWG |
| 20 A | 12 AWG |
| 30 A | 10 AWG |
| 40 A | 10 AWG |
| 60 A | 10 AWG |
| 100 A | 8 AWG |
| 200 A | 6 AWG |
| 300 A | 4 AWG |
| 400 A | 3 AWG |
| 500 A | 2 AWG |
| 600 A | 1 AWG |
| 800 A | 1/0 AWG |
| 1000 A | 2/0 AWG |
| 1200 A | 3/0 AWG |
| 1600 A | 4/0 AWG |
| 2000 A | 250 kcmil |
NEC Reference: The EGC runs with the branch circuit or feeder. For a 20 A overcurrent device, use minimum 12 AWG copper wire.
GEC vs. EGC: Understanding NEC Article 250
Grounding Electrode Conductor (GEC)
The GEC runs from the main service equipment to the grounding electrode system — typically ground rods, a water pipe, or a concrete-encased electrode (Ufer ground). Sized per NEC Table 250.66 based on the largest service entrance conductor size. Does not need to be larger than 3/0 AWG copper or 250 kcmil aluminum.
Equipment Grounding Conductor (EGC)
The EGC runs with every branch circuit and feeder to provide a fault return path back to the main panel. When a ground fault occurs, the EGC must carry enough current to trip the overcurrent device. Sized per NEC Table 250.122 based on the rating of the overcurrent protection device. May be bare, covered, or insulated — if insulated, must be green or green with yellow stripes.
NEC Table 250.122 — Equipment Grounding Conductors
Minimum EGC sizes for copper and aluminum conductors based on overcurrent protection device rating:
| OCD Rating | Min. Copper EGC | Min. Aluminum EGC |
|---|---|---|
| 15 A | 14 AWG | 12 AWG |
| 20 A | 12 AWG | 10 AWG |
| 30–60 A | 10 AWG | 8 AWG |
| 100 A | 8 AWG | 6 AWG |
| 200 A | 6 AWG | 4 AWG |
| 300 A | 4 AWG | 2 AWG |
| 400 A | 3 AWG | 1 AWG |
| 600 A | 1 AWG | 2/0 AWG |
| 800 A | 1/0 AWG | 3/0 AWG |
| 1000 A | 2/0 AWG | 4/0 AWG |
NEC Table 250.66 — Grounding Electrode Conductors
GEC sizes are based on the largest service-entrance conductor or the equivalent area of parallel conductors:
| Largest Service Conductor | Min. Copper GEC | Min. Aluminum GEC |
|---|---|---|
| 2 AWG or smaller | 8 AWG | 6 AWG |
| 1 AWG or 1/0 AWG | 6 AWG | 4 AWG |
| 2/0 or 3/0 AWG | 4 AWG | 2 AWG |
| Over 3/0 to 350 kcmil | 2 AWG | 1/0 AWG |
| Over 350 to 600 kcmil | 1/0 AWG | 3/0 AWG |
| Over 600 to 1100 kcmil | 2/0 AWG | 4/0 AWG |
| Over 1100 kcmil | 3/0 AWG | 250 kcmil |
Frequently Asked Questions
What is the difference between a GEC and an EGC?
A Grounding Electrode Conductor (GEC) connects your service equipment to the grounding electrode system (ground rods, water pipe, concrete-encased electrode, etc.) and is sized per NEC Table 250.66 based on your service entrance conductor size. An Equipment Grounding Conductor (EGC) runs with each branch circuit or feeder to provide a fault return path and is sized per NEC Table 250.122 based on the overcurrent protection device rating.
What size ground wire do I need for a 200 amp panel?
For a 200 amp residential service, the Equipment Grounding Conductor (EGC) from the main panel to a sub-panel is sized per NEC Table 250.122. For a 200A overcurrent device: minimum 6 AWG copper or 4 AWG aluminum. The Grounding Electrode Conductor (GEC) depends on your service entrance conductor size — typically 4 AWG copper for standard 200A copper service entrance conductors per Table 250.66.
What size ground wire for a 100 amp sub-panel?
Per NEC Table 250.122, the minimum equipment grounding conductor for a 100A overcurrent device is 8 AWG copper or 6 AWG aluminum. If the feeder conductors are oversized, the EGC must be proportionally increased as well per NEC 250.122(B).
Does aluminum wire work for grounding?
Yes. The NEC permits aluminum equipment grounding conductors and grounding electrode conductors. However, aluminum grounding conductors must be one size larger than equivalent copper to compensate for aluminum's lower conductivity. Use Tables 250.66 and 250.122 aluminum columns for sizing. Ensure all terminations are listed for use with aluminum conductors.
What is the minimum size ground wire for a 20 amp circuit?
Per NEC Table 250.122, a 20 amp overcurrent protection device requires a minimum 12 AWG copper or 10 AWG aluminum equipment grounding conductor. This is the minimum — you may always install a larger ground wire.
Specific Sizing Guides & Calculators
Related Calculators
Conduit Fill Calculator
Calculate NEC-compliant conduit fill percentages.
Voltage Drop Calculator
Determine voltage drop across wire runs.
Breaker Size Calculator
Find the correct breaker size for your circuit.
Wire Gauge Chart
Reference AWG diameters, ampacities, and limits.
Box Fill Calculator
Verify NEC 314.16 junction box fill compliance.
Conduit Bending Calculator
Calculate offset, saddle, and stub-up bend marks.
EV Charger Calculator
Size Level 2 EV charger circuits per NEC 625.42.