When an electrician or DIYer searches for a 'ground ampacity chart,' they are almost always looking for NEC Table 250.122. This table dictates the minimum size for an Equipment Grounding Conductor (EGC) based on the rating of the overcurrent protective device (breaker or fuse) protecting the circuit. The direct answer for standard residential branch circuits is simple: a 15A breaker requires a 14 AWG copper ground, and a 20A breaker requires a 12 AWG copper ground. But as circuits scale up to subpanels, EV chargers, and heavy machinery, the sizing rules require strict adherence to the National Electrical Code (NEC).
Unlike current-carrying conductors, the EGC only carries current during a fault condition. Its job is to provide a low-impedance path back to the source to trip the breaker instantly. Sizing it incorrectly can result in a fire hazard or a breaker that fails to trip during a short circuit. Below is the complete reference chart, followed by the critical edge cases that catch most installers off guard.
The Complete Ground Ampacity Chart (NEC Table 250.122)
How to read this table: Unlike the ampacity charts for hot and neutral wires (NEC Table 310.16), the ground ampacity chart does not use temperature columns (60°C, 75°C, 90°C). Because the EGC only handles brief fault currents, its continuous thermal rating is irrelevant. You size the EGC strictly by the breaker/fuse rating and the conductor material (Copper or Aluminum). Bookmark the 60A, 100A, and 200A rows, as these are the most frequently queried sizes for residential subpanels, EV chargers, and heat pumps.
| Overcurrent Device Rating (Amps) | Minimum Copper EGC (AWG/kcmil) | Minimum Aluminum EGC (AWG/kcmil) |
|---|---|---|
| 15 | 14 | 12 |
| 20 | 12 | 10 |
| 30 | 10 | 8 |
| 40 | 10 | 8 |
| 50 | 10 | 8 |
| 60 | 10 | 8 |
| 100 | 8 | 6 |
| 110 | 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 kcmil |
Critical Rules: Upsizing, Derating, and What the Chart Misses
Pulling the correct row from the table above is only the first step. Real-world installations frequently trigger NEC rules that force you to deviate from the base chart values. According to EC&M's guide on sizing EGCs, ignoring these modifiers is one of the most common reasons for failed electrical inspections.
Voltage Drop Upsizing (NEC 250.122(B))
If you increase the size of your ungrounded (hot) conductors to compensate for voltage drop on a long run, you must proportionally increase the size of the EGC. The chart does not account for this.
Worked Example: You are wiring a 60A EV charger located 150 feet from the panel. To keep voltage drop under 3%, you upsize your copper hot wires from 6 AWG to 4 AWG (an increase of two AWG steps). The chart above says a 60A breaker requires a 10 AWG copper ground. However, because you upsized the hots by two steps, you must upsize the ground by two steps as well: from 10 AWG to 6 AWG. If you pull a 10 AWG ground with 4 AWG hots, you will fail inspection.
Do Derating Factors Apply to Grounds?
A common point of confusion is conduit fill and ambient temperature derating (NEC 310.15(C)(1)). These derating factors apply only to current-carrying conductors. Because an EGC carries zero current under normal operation, you do not apply ambient temperature or conduit fill ampacity derating to the ground wire. However, the EGC does count toward the physical cross-sectional area when calculating maximum conduit fill capacity (NEC Chapter 9, Table 1).
What the Chart Cannot Tell You (EGC vs. GEC)
NEC Table 250.122 sizes the Equipment Grounding Conductor (EGC)—the wire that runs alongside your hot wires to provide a fault path back to the panel. It does not size the Grounding Electrode Conductor (GEC). The GEC is the wire that connects your main service panel to the earth (ground rods, ufer ground, or metal water pipe). Sizing a GEC requires an entirely different chart: NEC Table 250.66, which bases the ground size on the cross-sectional area of your largest service entrance conductor, not the main breaker size.
Pro-Tip for Metal Conduit: If you are pulling wires through rigid metal conduit (RMC) or intermediate metal conduit (IMC), the metal raceway itself is recognized by the NEC as an effective EGC. However, most inspectors and best-practice guidelines still require you to pull a dedicated copper EGC wire inside the conduit to ensure a continuous, low-impedance fault path that isn't reliant on the mechanical tightness of conduit couplings.
Ground Ampacity Chart FAQ
Do I need to increase my ground wire size for voltage drop?
Yes. Under NEC 250.122(B), if you upsize your ungrounded (hot) conductors to mitigate voltage drop, the equipment grounding conductor must be increased in size proportionally. If your hot wires go up by two AWG sizes, your ground wire must also go up by two AWG sizes from the baseline specified in Table 250.122.
Does the 90°C column apply to equipment grounding conductors?
No. NEC Table 250.122 does not use temperature columns (60°C, 75°C, or 90°C). Because the EGC only carries current during a brief short-circuit fault event, its continuous thermal insulation rating is irrelevant for sizing purposes. You select the wire size based purely on the breaker rating and whether the material is copper or aluminum.
Can I use a smaller ground wire if my actual load is much lower than the breaker size?
No. The EGC is sized based on the rating of the overcurrent protective device (the breaker or fuse), not the actual calculated load of the appliance. For example, if you have a 40A breaker protecting a circuit that only draws 25A in practice, you must still use the ground wire size specified for a 40A breaker (10 AWG copper). The ground wire must be capable of safely clearing the maximum fault current the breaker will allow before tripping.
What is the difference between an EGC and a GEC?
An Equipment Grounding Conductor (EGC) runs with your circuit conductors to bond metal enclosures and appliance frames back to the panel, providing a path for fault current to trip the breaker (sized via Table 250.122). A Grounding Electrode Conductor (GEC) connects the main service panel's neutral bus bar to the physical earth (ground rods, concrete-encased electrodes) to stabilize voltage and protect against lightning strikes (sized via Table 250.66).
