NEC Table 250.122 sizes the equipment grounding conductor from the rating of the overcurrent device ahead of the circuit — not from the circuit conductors. The four sizes that cover most residential work: 15 A → 14 AWG, 20 A → 12 AWG, up to 60 A → 10 AWG, up to 100 A → 8 AWG, all copper.
| Overcurrent device rating (A), not exceeding | Copper | Aluminum |
|---|---|---|
| 15 | 14 AWG | 12 AWG |
| 20 | 12 AWG | 10 AWG |
| 60 | 10 AWG | 8 AWG |
| 100 | 8 AWG | 6 AWG |
| 200 | 6 AWG | 4 AWG |
| 300 | 4 AWG | 2 AWG |
| 400 | 3 AWG | 1 AWG |
| 500 | 2 AWG | 1/0 AWG |
| 600 | 1 AWG | 2/0 AWG |
| 800 | 1/0 AWG | 3/0 AWG |
| 1000 | 2/0 AWG | 4/0 AWG |
| 1200 | 3/0 AWG | 250 kcmil |
| 1600 | 4/0 AWG | 350 kcmil |
| 2000 | 250 kcmil | 400 kcmil |
| 2500 | 350 kcmil | 600 kcmil |
| 3000 | 400 kcmil | 600 kcmil |
| 4000 | 500 kcmil | 750 kcmil |
| 5000 | 700 kcmil | 1200 kcmil |
| 6000 | 800 kcmil | 1200 kcmil |
250.122(A) — never smaller than the table, never larger than the circuit conductors. The equipment grounding conductor is not required to be larger than the ungrounded conductors it runs with. On a 60 A circuit wired with 6 AWG, the table already gives 10 AWG, so no conflict — but on tap conductors the rule matters.
250.122(B) — upsize the ground when you upsize the conductors. If the circuit conductors are increased in size for any reason — voltage drop being the common one — the equipment grounding conductor must be increased proportionally by circular mil area. Upsize a 20 A circuit from 12 AWG (6530 cmil) to 10 AWG (10380 cmil), a factor of 1.59, and the 12 AWG ground must grow by the same factor to at least 10380 cmil — 10 AWG.
250.122(F) — parallel runs. Where circuit conductors are run in parallel in multiple raceways, a full-size equipment grounding conductor sized from the overcurrent device must be run in each raceway. You do not divide it between them.
There is no 30 A, 40 A, or 50 A row in Table 250.122. The rows are maximum ratings — you round up to the next listed value. A 30 A dryer circuit, a 40 A range circuit, and a 50 A EV charger circuit all use the 60 A row and take a 10 AWG copper equipment grounding conductor.
This is why 10-3 NM-B cable ships with a 10 AWG bare ground, and why 6-3 NM-B for a 50 A circuit ships with a 10 AWG ground rather than a 6 AWG one. The ground only has to carry fault current long enough to open the breaker, not the continuous load.
The equipment grounding conductor (this table) is the fault-current path. It bonds metal enclosures and equipment back to the source so that a hot-to-case fault becomes a short circuit that trips the breaker. It is sized from the breaker because the breaker determines how much fault current has to flow before the circuit opens.
The grounding electrode conductor (Table 250.66) connects the system to earth. It stabilises voltage and handles lightning and line surges. It is sized from the service conductors. Earth is not a fault-current path and never has been.
NEC Table 250.122 gives the minimum size of equipment grounding conductor based on the rating of the overcurrent device protecting the circuit. It starts at 14 AWG copper for a 15 A breaker and runs to 800 kcmil copper for a 6000 A device.
10 AWG copper or 8 AWG aluminum. Table 250.122 has no 50 A row, so you round up to the 60 A row, which specifies 10 AWG copper. This is why 6-3 cable for a 50 A circuit ships with a 10 AWG ground.
8 AWG copper or 6 AWG aluminum, per the 100 A row of Table 250.122. In a sub-panel the equipment grounding conductor must land on an isolated ground bar, with the neutral bar kept separate and unbonded.
Yes. NEC 250.122(B) requires the equipment grounding conductor to be increased in the same proportion by circular mil area whenever the ungrounded conductors are increased in size, such as when compensating for voltage drop on a long run.