If you are sizing an equipment grounding conductor (EGC) for a standard branch circuit or feeder, the direct answer depends entirely on the rating of your overcurrent protective device (breaker or fuse). For standard copper wire: a 15A or 20A breaker requires 14 AWG or 12 AWG respectively; 30A through 60A breakers require 10 AWG; a 100A breaker requires 8 AWG; and a 200A breaker requires 6 AWG.
This guide provides the complete, code-compliant lookup chart so you can pull the right wire without a second trip to the supply house.
The NEC Ground Wire Size Table (NEC 250.122)
How to read this table: This data is sourced directly from NFPA 70 (National Electrical Code) Table 250.122. Unlike ungrounded (hot) conductors, equipment grounding conductors are not sized using the 60°C, 75°C, or 90°C ampacity columns. The EGC is sized strictly based on the ampere rating of the overcurrent device protecting the circuit. The values below represent the minimum circular mil area required to safely clear a fault current without melting. Always read across from your breaker size to find your minimum wire gauge.
| Breaker / Fuse Rating (Amps) | Minimum Copper EGC (AWG/kcmil) | Minimum Aluminum EGC (AWG/kcmil) |
|---|---|---|
| 15 | 14 | 12 |
| 20 | 12 | 10 |
| 30 | 10 | 8 |
| 40 | 10 | 8 |
| 60 | 10 | 8 |
| 100 | 8 | 6 |
| 110 | 6 | 4 |
| 200 | 6 | 4 |
| 300 | 4 | 2 |
| 400 | 3 | 1 |
Quick-Jump: Most Queried Residential & Workshop Values
For the most common DIY, residential, and light-commercial installations, bookmark these specific rows. Note that these assume standard copper conductors.
- 20A (Standard Receptacles & Lighting): 12 AWG Copper. (Even if you use 14 AWG for a 15A breaker, 12 AWG is the standard for 20A circuits).
- 30A (Dryers, RV Plugs, Small Compressors): 10 AWG Copper.
- 50A (Ranges, Welders, EV Chargers): 10 AWG Copper. Many DIYers mistakenly pull 8 AWG or 6 AWG ground for a 50A welder plug; 10 AWG is the legal minimum per 250.122.
- 100A (Subpanels, Detached Garages): 8 AWG Copper.
- 200A (Main Residential Service): 6 AWG Copper.
Decision Path: Which Column and Material Applies to You?
Use this decision tree to lock in your exact material and column choice. Do not mix materials on the same termination without approved bi-metallic lugs and anti-oxidant paste.
| Your Installation Scenario | Action | Concrete Pick |
|---|---|---|
| Pulling NM-B (Romex) inside walls | Use Copper column. The bare wire inside NM-B is pre-sized to code. | Bare Copper (Included in cable) |
| Pulling THHN/THWN-2 in PVC/EMT conduit | Use Copper column. Buy a spool of bare or green THHN. | Bare or Green Copper THHN |
| Running direct-burial URD or MHF feeder to a detached shop | Use Aluminum column to match your aluminum hot/neutral feeders. | Bare Aluminum (often pre-stripped from 4-wire URD) |
| Uncertain or mixing short conduit runs | Default to Copper. It terminates easier and resists corrosion better at standard lugs. | Copper Column (Default) |
When Derating and Upsizing Modify the Base Value
The most common error on the jobsite is assuming that because you had to derate or upsize your hot wires, you must do the same to the ground wire. This is only half true. According to Copper Development Association guidelines and NEC 250.122(B), the rules are highly specific:
1. Voltage Drop Upsizing (Triggers Ground Upsize)
If your circuit is long and you upsize the ungrounded (hot) conductors to mitigate voltage drop, you must proportionally upsize the EGC.
Worked Example: You are wiring a 50A EV charger 150 feet away. To keep voltage drop under 3%, you upsize the hots from 6 AWG to 4 AWG. Because the circular mil area of the hot wire increased by one standard size, you must increase the ground wire from the baseline 10 AWG to 8 AWG.
2. Conduit Fill / Ambient Temperature Derating (Does NOT Trigger Ground Upsize)
If you have 5 current-carrying conductors in a single conduit and must derate the ampacity of your hots by 80% (forcing you to use a larger hot wire), you do not need to upsize the ground. The EGC only carries current during a fault event, not during continuous operation, so ambient heat and conduit fill derating factors do not apply to its baseline sizing.
What This Table Cannot Tell You (Site-Specific Limits)
While NEC Table 250.122 covers 95% of residential and light-commercial wiring, it has blind spots. If your project falls into these categories, the table alone is insufficient:
- Available Fault Current (AFC): If your utility transformer is massive and located right outside your building, the available fault current might exceed 22,000 amps. Under OSHA and NEC 110.10 requirements, the equipment grounding conductor must be robust enough to withstand the magnetic and thermal forces of that specific fault current until the breaker trips. In high-AFC industrial settings, engineers often specify grounds two or three sizes larger than the 250.122 minimum.
- Parallel Conductor Runs: If you are feeding a 400A commercial panel using two parallel sets of 3/0 AWG wire in separate PVC pipes, you do not look at the 400A row and run a single 3 AWG ground. Per NEC 250.122(F), you must run a full-sized equipment grounding conductor in each parallel raceway, and each must be sized based on the rating of the single overcurrent device (meaning you would pull a 3 AWG ground in pipe A, and another 3 AWG ground in pipe B).
- Local AHJ Amendments: Some municipalities strictly mandate a minimum 10 AWG ground for all branch circuits, regardless of whether the breaker is 15A, to provide better physical durability and fault-clearing reliability. Always verify with your local inspector.
By anchoring your wire pulls to the breaker rating and applying the proportional increase rule only when voltage drop dictates, you will pass inspection and ensure your fault-current path is mechanically and electrically sound.
