NEC 250.122 · Equipment grounding
Minimum copper and aluminum EGC size by overcurrent-device rating, per NEC Table 250.122 — the ground-wire lookup you use sizing branch circuits and feeders.
| OCPD rating not exceeding (A) | Copper (AWG/kcmil) | Aluminum (AWG/kcmil) |
|---|---|---|
| 15 | 14 | 12 |
| 20 | 12 | 10 |
| 60 | 10 | 8 |
| 100 | 8 | 6 |
| 200 | 6 | 4 |
| 300 | 4 | 2 |
| 400 | 3 | 1 |
| 500 | 2 | 1/0 |
| 600 | 1 | 2/0 |
| 800 | 1/0 | 3/0 |
| 1000 | 2/0 | 4/0 |
| 1200 | 3/0 | 250 |
NEC Table 250.122 (sized by the rating of the overcurrent device ahead of the equipment). Table continues above 1200A (1600A → 4/0 Cu, 2000A → 250 kcmil Cu, etc.). Use the row whose OCPD rating is not exceeded by your device. Always verify against your adopted NEC edition.
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The equipment grounding conductor (EGC) is the conductor that bonds metal enclosures, raceways, and equipment back to the source so a fault clears the breaker. NEC Table 250.122 sizes it by the rating of the overcurrent device ahead of the equipment — not by the ungrounded conductor size. Find the row whose OCPD rating your breaker does not exceed, and read the copper or aluminum size.
Two rules ride along with the table. 250.122(A): the EGC never has to be larger than the circuit conductors. 250.122(B): if you upsize the phase conductors (for voltage drop, for example), you must upsize the EGC by the same area ratio — a frequent field miss.
Need the conductor ampacity to size those phase conductors? See the NEC 310.16 wire ampacity chart, and check long runs with the voltage drop calculator. Field PM keeps your panel schedules, equipment lists, and inspection records together on the job.
Per NEC Table 250.122, the minimum equipment grounding conductor for a 100 A overcurrent device is 8 AWG copper (or 6 AWG aluminum). For a 200 A device it is 6 AWG copper / 4 AWG aluminum; for a 60 A device, 10 AWG copper / 8 AWG aluminum.
By the rating of the overcurrent protective device (breaker or fuse) ahead of the equipment, using NEC Table 250.122 — not by the ungrounded conductor size. The one exception: per 250.122(A), the EGC never needs to be larger than the circuit conductors supplying the equipment.
Yes. NEC 250.122(B) requires that when ungrounded conductors are increased in size (for voltage drop or any reason), the equipment grounding conductor is increased proportionally by the same area ratio. A common field miss — the EGC has to grow with the phase conductors.
The equipment grounding conductor (EGC, Table 250.122) bonds equipment back to the source and is sized by the OCPD rating. The grounding electrode conductor (GEC, Table 250.66) connects the system to earth (ground rods, Ufer, water pipe) and is sized by the service/derived-system conductors. They are different conductors with different tables.
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