Ground Wire Size Chart: EGC (250.122) & GEC (250.66)
NEC 250 · Grounding · Updated 2026-07-10
"What size ground wire?" is really two different questions. The equipment grounding conductor (EGC) is sized from the breaker protecting the circuit - NEC Table 250.122. The grounding electrode conductor (GEC) is sized from the service-entrance conductors - Table 250.66.
Mix them up and you either waste copper or fail rough-in. Both charts below.
EGC size by overcurrent device (NEC Table 250.122)
| OCPD rating | Copper EGC | Aluminum EGC |
|---|---|---|
| 15 A | #14 | #12 |
| 20 A | #12 | #10 |
| 30 - 60 A | #10 | #8 |
| 70 - 100 A | #8 | #6 |
| 110 - 200 A | #6 | #4 |
| 225 - 300 A | #4 | #2 |
| 350 - 400 A | #3 | #1 |
| 450 - 500 A | #2 | 1/0 |
GEC size by service conductors (NEC Table 250.66)
| Service conductor (Cu) | Copper GEC |
|---|---|
| #2 or smaller | #8 |
| #1 or 1/0 | #6 |
| 2/0 or 3/0 | #4 |
| Over 3/0 through 350 kcmil | #2 |
| Over 350 through 600 kcmil | 1/0 |
| Over 600 through 1100 kcmil | 2/0 |
| Over 1100 kcmil | 3/0 |
- Ground rods, pipes, and plates: the GEC to those electrodes never needs to be larger than #6 copper (250.66(A)).
- Concrete-encased electrode (Ufer): max #4 copper (250.66(B)).
- Typical 200 A dwelling (2/0 Cu service): #4 Cu GEC to the water pipe, #6 Cu to the rods.
The upsizing trap: 250.122(B)
Upsize the circuit conductors for voltage drop and the EGC must grow proportionally to circular-mil area - not stay at the table minimum. Go from #12 (6,530 CM) to #8 (16,510 CM) on a long 20 A run, and the #12 EGC must scale by the same 2.53× ratio: 16,510 CM minimum, which lands on #8. Long runs often end up with a ground the same size as the hots.
EGC, GEC, and the proportional rule - handled. Conduit Fill & Bending Calc sizes grounds from the correct table, cited and inspector-ready. Free on the App Store. Download Conduit Fill & Bending Calc on the App Store.
Frequently asked questions
What size ground wire do I need for 100 amps?
If you mean the equipment ground for a 100 A breaker: #8 copper or #6 aluminum (Table 250.122). If you mean the grounding electrode conductor for a 100 A service with #4 Cu service conductors: #8 copper (Table 250.66).
What size ground wire for a 200 amp service?
The GEC for a typical 200 A dwelling service (2/0 copper service conductors) is #4 copper - though only #6 copper is required if it runs solely to ground rods. A 200 A feeder's EGC is #6 copper per 250.122.
Do I need a bigger ground wire if I upsize for voltage drop?
Yes. NEC 250.122(B) requires the EGC to increase in proportion to the circular-mil growth of the ungrounded conductors. Upsizing hots 2.5× means the ground's circular-mil area grows 2.5× too.
Why is the wire to a ground rod only #6?
Because a rod electrode's earth connection is the bottleneck - a larger conductor can't deliver more current into soil than the rod itself can. NEC 250.66(A) therefore caps the required GEC to rod, pipe, or plate electrodes at #6 copper.