The size of your Equipment Grounding Conductor (EGC) is not determined by the expected continuous load current, but strictly by the rating of the Overcurrent Protective Device (OCPD)—the breaker or fuse—protecting the circuit. If you are looking for a grounding ground wire size chart, you need to reference NEC Table 250.122. For a standard 20A branch circuit, you must use a minimum of 12 AWG copper. For a 60A feeder, you need 10 AWG copper. For a 100A subpanel feeder, the minimum is 8 AWG copper.
Before pulling wire, it is critical to distinguish between the Equipment Grounding Conductor (EGC, which clears faults on branch circuits and feeders) and the Grounding Electrode Conductor (GEC, which connects your main panel to a ground rod or water pipe). The chart below covers the EGC (NEC 250.122), which applies to 95% of residential and commercial wiring projects. (For GEC sizing to ground rods, refer to NEC Table 250.66).
The NEC Table 250.122 Grounding Ground Wire Size Chart
How to read this table: Locate the rating of your breaker or fuse in the left column. Read across to the Copper or Aluminum column based on your conductor material. The values represent the minimum required AWG or kcmil size. You may always use a larger wire, but never smaller. This table assumes standard installation conditions; it does not account for voltage drop upsizing, which is covered in the next section.
• 15A / 20A (Standard Outlets/Lighting): 14 AWG / 12 AWG
• 30A (Dryers/Water Heaters): 10 AWG
• 60A (EV Chargers/Small Subpanels): 10 AWG
• 100A (Main Subpanel Feeders): 8 AWG
• 200A (Whole House Subpanel): 6 AWG
| OCPD Rating (Amps) | Copper EGC Size (AWG/kcmil) | Aluminum EGC Size (AWG/kcmil) |
|---|---|---|
| 15 | 14 | 12 |
| 20 | 12 | 10 |
| 30 | 10 | 8 |
| 40 | 10 | 8 |
| 50 | 10 | 8 |
| 60 | 10 | 8 |
| 100 | 8 | 6 |
| 110 | 6 | 4 |
| 200 | 6 | 4 |
| 250 | 4 | 2 |
| 300 | 4 | 2 |
| 400 | 3 | 1 |
| 500 | 2 | 1/0 |
| 600 | 1 | 1/0 |
Which Column Applies and the Voltage Drop Upsize Rule
For nearly all residential and light commercial branch circuits and feeders, the Copper column applies. NM-B (Romex), UF-B, and standard THHN/THWN-2 pulled in conduit utilize copper equipment grounding conductors. The Aluminum column is primarily used in heavy commercial or industrial feeders where the ungrounded (hot) conductors are also aluminum (e.g., XHHW-2 in a large trough or underground PVC). Never mix copper and aluminum conductors in the same cable assembly or raceway without approved anti-oxidant compound and specific terminal ratings.
The chart above only provides the minimum baseline. If you increase the size of your ungrounded (hot) conductors to compensate for voltage drop over a long distance, NEC 250.122(B) mandates that you must proportionally increase the size of your equipment grounding conductor.
Worked Example: The Voltage Drop Upsize
Imagine you are wiring a detached garage subpanel. You have a 60A breaker. According to the chart, the baseline ground wire is 10 AWG copper. However, the run is 180 feet long. To keep voltage drop under 3% at a 48A continuous load, you calculate that you need to upsize your hot wires from the baseline 4 AWG up to 2 AWG copper.
Because you jumped two AWG sizes on the hot wires (4 AWG → 3 AWG → 2 AWG), you must jump two AWG sizes on the ground wire. The ground wire must go from 10 AWG → 8 AWG → 6 AWG. If you pull 2 AWG hots but leave a 10 AWG ground in that conduit, your installation will fail inspection. The fault current path must have proportionally lower impedance to ensure the 60A breaker trips instantaneously during a dead short at the far end of the long run.
What the Table Cannot Tell You: Parallel Runs and Raceways
While Table 250.122 is the definitive baseline, it does not cover every physical installation scenario. Here are the edge cases where the chart alone will lead you astray:
1. Parallel Feeder Runs (NEC 250.122(F))
When wiring large services (typically 400A to 1200A), electricians run multiple parallel conduits rather than one massive cable. If you are running two parallel sets of 350 kcmil copper protected by a single 800A main breaker, you do not pull one giant ground wire in a single conduit. Instead, you must pull an equipment grounding conductor in every single parallel raceway. Furthermore, each individual ground wire must be sized based on the total 800A OCPD rating (which calls for 1/0 AWG copper per raceway), not the ampacity of the individual conductors inside that specific pipe. The code explicitly states parallel EGCs cannot be smaller than 1/0 AWG.
2. Metal Raceways as the EGC
The chart assumes you are pulling a dedicated wire. However, under NEC 250.118, certain metal raceways and cable armors are legally permitted to serve as the equipment grounding conductor themselves. Rigid Metal Conduit (RMC), Intermediate Metal Conduit (IMC), and properly coupled Electrical Metallic Tubing (EMT) can act as your ground path. If you are pulling THHN through properly installed EMT with set-screw or compression fittings, you technically do not need to pull a separate green or bare copper wire for a 20A circuit. (Note: Many local AHJs and commercial specs still require a dedicated "green wire" pulled alongside the EMT for redundant fault clearing, so always verify with your inspector).
3. Flexible Cords and Fixture Wires
Table 250.122 does not apply to flexible cords (like SOOW or SJOOW) used for portable tools or appliances. Flexible cords must contain an equipment grounding conductor sized according to NEC Table 400.12, which correlates to the cord's overall gauge and application, not just the breaker rating. Similarly, internal fixture wires inside lighting housings follow different rules based on the specific UL listing of the luminaire.
For further reading on the physics of fault current paths and the exact mathematical derivation of these tables, refer to the NFPA 70 National Electrical Code documentation and the Electrical Training Alliance curriculum on grounding and bonding principles.
