NEC Table 250.122: ground wire size by breaker rating
The equipment grounding conductor (EGC) is the bare, green or green-with-yellow wire that carries fault current back to the panel so the breaker trips. NEC 250.122 sizes it from the rating of the breaker or fuse protecting the circuit, not from the load. Find the first row whose rating is not smaller than your breaker.
| Breaker or fuse up to | Copper ground | Aluminum ground |
|---|---|---|
| 15 A | 14 AWG | 12 AWG |
| 20 A | 12 AWG | 10 AWG |
| 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 |
| 500 A | 2 AWG | 1/0 AWG |
| 600 A | 1 AWG | 2/0 AWG |
| 800 A | 1/0 AWG | 3/0 AWG |
| 1,000 A | 2/0 AWG | 4/0 AWG |
| 1,200 A | 3/0 AWG | 250 kcmil |
| 1,600 A | 4/0 AWG | 350 kcmil |
| 2,000 A | 250 kcmil | 400 kcmil |
Table 250.122 continues above 2,000 A. A 30 A or 40 A or 50 A breaker uses the 60 A row, so the ground is 10 AWG copper. A 70 A to 100 A breaker uses 8 AWG copper.
Example
A 50 A electric range circuit with 6 AWG hot wires needs a 10 AWG copper ground, because 50 A falls in the 60 A row. A 20 A kitchen circuit needs 12 AWG, which is why 12/2 NM cable has a 12 AWG bare ground. The ground is never required to be larger than the hot conductors (250.122(A)).
Upsizing the ground when you upsize the hot wires
If you increase the hot conductors for any reason other than ambient temperature or bundling, 250.122(B) says the ground must grow in proportion. Long runs sized for voltage drop are the usual case. The calculator multiplies the Table 250.122 circular-mil area by the ratio of the installed hot wire to the standard hot wire, then rounds up to the next size.
Example: a 20 A circuit normally uses 12 AWG (6,530 circular mils). Running 8 AWG (16,510 circular mils) for distance gives a ratio of 2.53, so the ground becomes 8 AWG copper too. Use the voltage drop calculator to decide whether you need the larger hot wire at all.
Service grounding electrode conductor (NEC Table 250.66)
A different table sizes the wire that runs from the main panel to the ground rod, water pipe or concrete-encased electrode. It depends on the size of the service-entrance conductors, not the breaker:
| Largest copper service conductor | Copper electrode wire | Aluminum electrode wire |
|---|---|---|
| 2 AWG or smaller | 8 AWG | 6 AWG |
| 1 AWG or 1/0 | 6 AWG | 4 AWG |
| 2/0 or 3/0 | 4 AWG | 2 AWG |
| Over 3/0 through 350 kcmil | 2 AWG | 1/0 AWG |
| Over 350 through 600 kcmil | 1/0 AWG | 3/0 AWG |
A typical 200 A dwelling service uses 2/0 copper (or 4/0 aluminum) conductors, so the electrode wire is 4 AWG copper. If the wire goes only to a ground rod, 250.66(A) does not require more than 6 AWG copper, and to a concrete-encased electrode it need not exceed 4 AWG copper. See the 200 amp service wire size guide for the full set.
Frequently asked questions
What size ground wire for a 20 amp circuit?
12 AWG copper, or 10 AWG aluminum. That is the Table 250.122 row for breakers up to 20 A.
What size ground wire for a 50 amp breaker?
10 AWG copper or 8 AWG aluminum, because 50 A falls in the 60 A row of the table.
What size ground wire for a 100 amp panel?
For a 100 A feeder breaker the equipment ground is 8 AWG copper or 6 AWG aluminum. The grounding electrode conductor at a 100 A service depends on the service wire size: usually 8 AWG copper.
Can the ground wire be smaller than the hot wires?
Yes, in the normal case. The 250.122 table gives smaller sizes than the circuit conductors above 15 A. The ground is not required to be larger than the hot wires, and must be increased only if the hot wires are upsized.
Sources
Reference charts
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