When DIYers and apprentices search for an "NEC grounding chart," they are usually looking for one of two completely different tables in the National Electrical Code (NFPA 70). If you are running a feeder to a subpanel, wiring a hot tub, or installing an EV charger, you need NEC Table 250.122 for the Equipment Grounding Conductor (EGC). If you are connecting a main service panel to a ground rod or ufer ground, you need NEC Table 250.66 for the Grounding Electrode Conductor (GEC).
Mixing these up is a common jobsite error. The EGC provides a low-impedance fault-current path back to the source to trip the breaker. The GEC connects your electrical system to the earth to stabilize voltage and dissipate lightning strikes. Below are the complete, bookmark-friendly reference tables for both, based on the 2023/2026 NEC cycle.
How to Read the NEC Grounding Chart
Before jumping to the rows, you must understand how the NEC derives these numbers. Unlike the ampacity tables (NEC 310.16) which size your hot and neutral wires based on the wire's thermal limits, the grounding tables size your ground wire based on the overcurrent device's rating.
Which column applies to your installation?
Look at the rating of the breaker or fuse protecting the circuit, not the ampacity of the wire you pulled. For example, if you pulled 10 AWG THHN (rated 35A at 90°C) for a 20A branch circuit, you do not use the 35A row. You use the 20A row. The ground wire only needs to handle fault current long enough for the 20A breaker to trip, which dictates a 12 AWG copper EGC.
Temperature Ratings and Materials:
The EGC table does not use the 60°C, 75°C, or 90°C columns found in standard ampacity charts. You simply choose between the Copper or Aluminum column. However, if you are using NM-B (Romex) cable, the internal bare copper ground is pre-sized by the manufacturer to meet Table 250.122 for the cable's rated ampacity. When pulling individual THHN/THWN-2 conductors in conduit, you must pull a separate insulated (green) or bare copper EGC sized per the chart below.
NEC Table 250.122: Equipment Grounding Conductor (EGC) Sizes
This is the chart you need for branch circuits, feeders, subpanels, and hardwired appliances. Source: NFPA 70, NEC Table 250.122.
| Overcurrent Device Rating (Amps) | Copper EGC (AWG/kcmil) | Aluminum EGC (AWG/kcmil) | Common Application Notes |
|---|---|---|---|
| 15 | 14 | 12 | Standard 15A lighting/outlet circuits |
| 20 | 12 | 10 | Standard 20A kitchen/garage circuits |
| 30 | 10 | 8 | Dryers, water heaters, small AC |
| 40 | 10 | 8 | Electric ranges (older 40A setups) |
| 50 | 10 | 8 | EV Chargers (Level 2), Hot Tubs |
| 60 | 10 | 8 | 60A subpanels, large welders |
| 100 | 8 | 6 | Standard 100A detached garage subpanel |
| 110 | 8 | 6 | Specialty HVAC equipment |
| 200 | 6 | 4 | 200A main service feeders / large subpanels |
| 225 | 6 | 4 | Heavy commercial feeders |
| 300 | 4 | 2 | Large residential / light commercial mains |
| 400 | 3 | 1 | 400A residential split services |
| 500 | 2 | 1/0 | Commercial service feeders |
| 600 | 1 | 2/0 | Maximum standard molded-case breaker size |
NEC Table 250.66: Grounding Electrode Conductor (GEC) Sizes
Use this table only when sizing the wire that connects your service panel's neutral/ground busbar to the physical earth (ground rods, metal underground water pipe, or concrete-encased Ufer ground). Source: ECM Web / NEC Table 250.66.
| Service Entrance Conductor Size (Copper) | Service Entrance Conductor Size (Aluminum) | Required Copper GEC Size |
|---|---|---|
| 2 AWG or smaller | 1/0 AWG or smaller | 8 AWG |
| 1/0 AWG | 2/0 AWG | 8 AWG |
| 2/0 AWG to 3/0 AWG | 3/0 AWG to 4/0 AWG | 6 AWG |
| 4/0 AWG to 350 kcmil | 250 kcmil to 500 kcmil | 4 AWG |
| Over 350 kcmil to 600 kcmil | Over 500 kcmil to 900 kcmil | 2/0 AWG |
| Over 600 kcmil to 1100 kcmil | Over 900 kcmil to 1750 kcmil | 3/0 AWG |
Derating, Voltage Drop, and What the Table Cannot Tell You
The charts above provide the minimum baseline sizes. In real-world installations, three major factors force you to deviate from the base table values.
1. Voltage Drop Upsizing (NEC 250.122(B))
This is the most frequently missed code violation on long feeder runs. Standard ampacity derating (bundling wires in a hot attic, for instance) does not directly change the ground wire size. However, if you upsize your ungrounded (hot) conductors to mitigate voltage drop on a long run, you must proportionally upsize the EGC.
Worked Example: You are wiring a 60A subpanel 150 feet away. To keep voltage drop under 3%, you upsize your hot wires from the standard 6 AWG copper to 4 AWG copper. The area of 4 AWG is roughly 1.6 times larger than 6 AWG. Therefore, your ground wire must also increase in area by that ratio. The baseline 60A ground is 10 AWG. Upsizing it proportionally means you must pull an 8 AWG ground, not a 10 AWG.
2. Parallel Conductors
If your service or feeder is so large that you are running parallel sets of conductors (e.g., two sets of 500 kcmil per phase), you cannot just run one massive ground wire. NEC 300.3(B) and 250.122(F) require that an EGC must be run in each raceway or cable assembly, and each individual EGC must be sized per Table 250.122 based on the rating of the single overcurrent device protecting the entire parallel set.
3. What the Table Cannot Tell You
- Physical Protection: If you are running an exposed ground wire along a masonry wall or in an area subject to physical damage, the NEC requires it to be protected by conduit or armor, regardless of the AWG size.
- Busbar Sizing: The table tells you the wire size, but it does not tell you how to size the grounding busbar inside a subpanel. The busbar must have a cross-sectional area equal to or greater than the largest EGC connected to it.
- Insulation Color: While bare copper is universally accepted, if you use an insulated ground wire in a conduit, it must be green, or green with one or more yellow stripes (NEC 250.119). You cannot use white or black THHN and wrap it in green tape at the terminals for a permanent installation.
Frequently Asked Questions
What size ground wire for 100 amp service NEC?
It depends on which part of the 100A service you are wiring. If you are pulling a feeder from the main panel to a 100A subpanel, you are sizing an Equipment Grounding Conductor (EGC) per Table 250.122, which requires an 8 AWG copper or 6 AWG aluminum wire. If you are wiring the main 100A service disconnect to a ground rod (Grounding Electrode Conductor), Table 250.66 requires an 8 AWG copper wire (assuming your service entrance conductors are 2 AWG copper or 1/0 AWG aluminum).
Do I need to upsize my ground wire for a long run?
Yes, but only if you upsize your hot wires first. The NEC does not mandate voltage drop corrections, but if you choose to upsize your ungrounded (hot) conductors to compensate for voltage drop on a long run, NEC 250.122(B) legally requires you to upsize the equipment grounding conductor in the exact same proportion. If your hot wires go up two AWG sizes to fight voltage drop, your ground wire must also go up two AWG sizes to maintain the same impedance ratio and ensure the breaker trips fast enough during a fault at the far end of the run.
Can I use the metal conduit as my ground wire instead of pulling a separate EGC?
Technically, rigid metal conduit (RMC) and intermediate metal conduit (IMC) are recognized by the NEC as an acceptable Equipment Grounding Conductor if all fittings are listed for grounding and properly tightened. However, most modern electricians and local AHJs strongly prefer (or outright mandate) pulling a separate, dedicated copper EGC wire inside the conduit. Standard EMT (Electrical Metallic Tubing) is also listed as an EGC, but its setscrew couplings can loosen over time or fail to provide a reliable low-impedance path under heavy fault currents. Pulling a dedicated wire guarantees a reliable fault path and saves you from failed inspections.
What is the difference between Table 250.122 and 250.66?
Table 250.122 sizes the Equipment Grounding Conductor (EGC), which is the bare or green wire that runs alongside your hot and neutral wires to provide a fault-current path back to the breaker panel. It is sized based on the breaker rating. Table 250.66 sizes the Grounding Electrode Conductor (GEC), which is the wire that connects your main electrical panel to the physical earth (like a ground rod or ufer). It is sized based on the physical size of your main service entrance cables, not the breaker rating.
