The size of your Equipment Grounding Conductor (EGC) is dictated entirely by the rating of the overcurrent protective device (breaker or fuse) protecting the circuit, not by the actual load current. For a standard 20A residential branch circuit, you need a minimum 12 AWG copper EGC. For a 100A subpanel feeder, you need an 8 AWG copper EGC. If you are pulling aluminum, you must step up one or two sizes depending on the breaker rating.
This guide provides the complete equipment grounding chart derived from NFPA 70 (National Electrical Code) Table 250.122, along with the exact decision paths required when voltage drop calculations force you to upsize your ungrounded (hot) conductors.
How to Read the NEC Equipment Grounding Chart
Before pulling wire, you need to understand how the NEC structures grounding requirements. Unlike current-carrying conductors, EGCs do not carry current under normal operation. They only carry fault current long enough for the breaker to trip. Because of this, the sizing rules are fundamentally different.
When sizing hot and neutral wires, you must consult the 60°C, 75°C, or 90°C ampacity columns in NEC Table 310.16. Ignore those columns for EGCs. Equipment grounding conductor sizing is strictly tied to the breaker size via Table 250.122, regardless of whether you are using 60°C NM-B (Romex) or 90°C THHN in conduit.
The chart below features two primary material columns: Copper and Aluminum (or Copper-Clad Aluminum). Always default to the copper column unless you are explicitly pulling aluminum feeder cables (like SER or XHHW-2 AL). If your breaker size falls between two values on the chart (e.g., a 70A breaker), you must round up to the next highest listed breaker size (100A) to find your minimum wire gauge.
The Master Equipment Grounding Chart (NEC Table 250.122)
The following data is sourced directly from NFPA 70 (NEC) Table 250.122. Bookmark this section for quick jobsite lookups. The most commonly queried residential and light-commercial rows are highlighted.
| Overcurrent Device Rating (Amps) | Minimum Copper EGC (AWG/kcmil) | Minimum Aluminum EGC (AWG/kcmil) |
|---|---|---|
| 15A | 14 | 12 |
| 20A (Standard Receptacles) | 12 | 10 |
| 30A (Dryers/Water Heaters) | 10 | 8 |
| 40A (Ranges/Cooktops) | 10 | 8 |
| 50A (Hot Tubs/Welders) | 10 | 8 |
| 60A | 10 | 8 |
| 100A (Standard Subpanel) | 8 | 6 |
| 110A | 8 | 6 |
| 150A | 8 | 6 |
| 200A (Main Residential Service) | 6 | 4 |
| 300A | 4 | 2 |
| 400A | 3 | 1 |
| 500A | 2 | 1/0 |
| 600A | 1 | 2/0 |
| 800A | 1/0 | 3/0 |
| 1000A | 2/0 | 4/0 |
| 1200A | 3/0 | 250 kcmil |
Decision Path: Sizing Your EGC for Real-World Installations
Reading the base table is only step one. Real-world installations frequently require adjustments. Use this decision tree to determine your exact wire size.
| Installation Scenario | NEC Rule | Action Required | Final Concrete Pick |
|---|---|---|---|
| Standard Branch Circuit (Run under 100ft, no voltage drop calc needed) |
250.122(A) | Look up breaker size on the master chart. Pull standard NM-B or THHN. | For a 20A breaker: 12 AWG Copper. |
| Long-Run Feeder (Upsized ungrounded hots for voltage drop) |
250.122(B) | Calculate the circular mil ratio of the upsized hot wire vs. the base hot wire. Multiply the base EGC circular mils by this ratio. | See worked example below. |
| Metal Raceway Used as EGC (EMT, Rigid, or IMC conduit) |
250.118 & 250.122 | The metal conduit itself qualifies as the EGC. No wire pull required, but fittings must be wrench-tight to ensure continuity. | For 3/4" EMT on a 60A circuit: No wire needed (Conduit is the EGC). |
| Multi-Wire Branch Circuit (MWBC) (Shared neutral, multiple breakers) |
250.122(A) | Size the EGC based on the largest overcurrent device protecting any of the ungrounded conductors in the raceway. | For a 20A/15A MWBC: 12 AWG Copper (based on the 20A breaker). |
Worked Example: Proportional Upsizing (NEC 250.122(B))
Let’s say you are installing a 100A subpanel feeder 200 feet away. To keep voltage drop under 3%, your calculations show you must upsize your ungrounded (hot) conductors from the standard 3 AWG copper (rated for 100A at 75°C) to 1 AWG copper.
According to EC&M's analysis of NEC grounding rules, you cannot just use the 8 AWG EGC listed in Table 250.122. You must upsize the EGC proportionally based on the circular mil (cmil) area of the wires.
- Base Hot Wire (3 AWG): 52,620 cmil
- Upsized Hot Wire (1 AWG): 83,690 cmil
- Upsize Ratio: 83,690 / 52,620 = 1.59
- Base EGC (8 AWG): 16,510 cmil
- Required EGC cmil: 16,510 × 1.59 = 26,250 cmil
Looking at NEC Chapter 9, Table 8, a 6 AWG copper wire is 26,240 cmil (effectively identical), while a 4 AWG is 41,740 cmil. Your final concrete pick is a 6 AWG copper EGC. Never downsize this proportionally calculated wire back to the table minimum.
What This Chart Cannot Tell You
While Table 250.122 is the definitive guide for branch circuits and feeders, it has strict boundaries. Do not use this equipment grounding chart for the following scenarios:
- Grounding Electrode Conductors (GEC): The wire connecting your main service panel to the ground rods, ufer ground, or water pipe is a GEC, not an EGC. GEC sizing is governed by NEC Table 250.66, which is based on the size of the largest ungrounded service entrance conductor, not the breaker size.
- Parallel Conductor Installations: If you are pulling parallel sets of wire for a massive 800A feeder (per NEC 310.10(H)), you do not use one massive EGC. Under NEC 250.122(C), you must pull a separate EGC in each parallel raceway, and each EGC must be sized to the full breaker rating from Table 250.122, or you must use a single EGC sized to the total combined kcmil of all parallel hots.
- Flexible Cords and Fixture Wires: If you are wiring a pendant light or a flexible appliance cord, Table 250.122 does not apply. Flexible cords are governed by NEC 250.114 and 400.23, which tie the ground wire size directly to the gauge of the cord's current-carrying conductors.
Always de-energize the panel, lock out the main breaker, and verify zero voltage with a tested CAT III or CAT IV multimeter before terminating any EGC to a panel ground bar. Ensure the ground bar is isolated from the neutral bar in subpanels (bond screw removed). The NEC provides the baseline framework, but your local Authority Having Jurisdiction (AHJ) or municipal inspector always has the final say on code compliance and acceptable local amendments.
