If you are looking for the direct answer: for standard residential branch circuits, a 15A or 20A breaker requires a 14 AWG or 12 AWG copper ground wire, respectively. A 30A to 60A breaker requires a 10 AWG copper ground, and a 100A feeder requires an 8 AWG copper ground. However, blindly following these baseline numbers without understanding the National Electrical Code (NEC) rules for voltage drop upsizing and parallel runs is how inspectors fail rough-ins and how fault currents melt undersized conductors.

This guide provides the complete ground wire chart based on NEC Table 250.122, decodes the specific columns you need, and explains the critical proportional upsizing math that most online guides completely ignore.

Bookmark These: The 5 Most Common Residential Sizes (Copper)
  • 15A / 20A Branch Circuits: 14 AWG / 12 AWG (Matches the hot wire size)
  • 30A Dryer / 40A Range / 50A Hot Tub: 10 AWG
  • 60A Subpanel Feeder: 10 AWG
  • 100A Subpanel Feeder: 8 AWG
  • 200A Main Service Feeder: 6 AWG

The Master Ground Wire Chart (NEC Table 250.122)

The following 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. This data is sourced directly from NFPA 70 (National Electrical Code), specifically Table 250.122.

Overcurrent Device Rating (Amps) Copper Wire Size (AWG/kcmil) Aluminum Wire Size (AWG/kcmil)
151412
201210
30108
40108
50108
60108
10086
11086
12586
15064
17564
20064
22564
25042
30042
35031
40031

How to Read the Chart and Pick Your Column

Reading a ground wire chart correctly requires understanding three foundational rules that dictate which row and column apply to your specific installation.

1. Match the Breaker, Not the Load: The left column is labeled "Overcurrent Device Rating." You must size the ground wire based on the breaker protecting the circuit, not the actual continuous load of the appliance. If you have a 45A continuous load on a 60A breaker, you look at the 60A row, not a hypothetical 45A row.

2. Copper vs. Aluminum: Always use the Copper column for standard NM-B (Romex) and THHN in residential branch circuits. Use the Aluminum column only when pulling heavy feeder cables (like 4-4-4-6 Dyke or XHHW-2) into subpanels where aluminum is used for cost savings on the ungrounded (hot) and neutral conductors.

3. The "Next Size Up" Rule: If your breaker size falls between the rows listed (for example, a 70A breaker), the NEC requires you to move down to the next highest listed rating. For a 70A breaker, you would use the 100A row, requiring an 8 AWG copper ground.

Safety Caveat: The EGC must never be smaller than the required ungrounded (hot) conductor. On a 20A circuit using 12 AWG copper hots, the chart says 12 AWG ground. You cannot use 14 AWG ground just because a 15A breaker would theoretically allow it if you swapped the breaker later. The ground must match the physical wire size of the circuit conductors if the chart dictates a smaller wire than what is in the cable.

The Upsizing Rule: When the Chart Fails You

This is where amateur electricians fail inspections and where the ground wire chart alone is insufficient. There is a massive difference between ampacity derating and voltage drop upsizing.

Derating Does NOT Modify the Ground: If you have more than three current-carrying conductors in a single conduit, NEC 310.15 requires you to derate the ampacity of the hot and neutral wires. Because the equipment grounding conductor only carries current during a fault, it is not considered a current-carrying conductor. Therefore, heat derating does not force you to upsize the ground wire.

Voltage Drop DOES Modify the Ground: If your circuit run is exceptionally long (typically over 100 feet), you must upsize the hot wires to prevent voltage drop. Under NEC 250.122(B), if you increase the size of the ungrounded conductors for voltage drop, you must proportionally increase the size of the equipment grounding conductor based on circular mil area.

Worked Numeric Example: 50A Hot Tub at 150 Feet

  • Base Requirement: 50A breaker. Chart dictates 6 AWG THHN hots and 10 AWG copper ground.
  • Voltage Drop Fix: At 150 feet, 6 AWG copper yields a 4.1% voltage drop (exceeding the 3% recommended limit). You must upsize the hots to 4 AWG.
  • Circular Mil Math: 6 AWG = 26,240 cmil. 4 AWG = 41,740 cmil. The ratio is 41,740 / 26,240 = 1.59.
  • Ground Upsize: Base 10 AWG ground = 10,380 cmil. Multiply by 1.59 = 16,504 cmil.
  • Final Pick: Looking at NEC Chapter 9, Table 8, an 8 AWG wire is 16,510 cmil. Therefore, your ground wire must be upsized from 10 AWG to 8 AWG.

Decision Path: Sizing Your EGC in 4 Steps

Use this decision-tree to terminate your sizing process with a single, concrete wire pick. For deeper code interpretations, reference the grounding resources at Mike Holt Enterprises.

Scenario Condition If True... Concrete Action / Pick
Standard run under 100 ft Use baseline chart. Pick the exact AWG from Table 250.122 matching your breaker.
Run exceeds 100 ft (Voltage Drop) Calculate cmil ratio of upsized hots. Multiply base ground cmil by ratio; pick next largest AWG from Ch.9 Table 8.
Using metal conduit (EMT/Rigid) as EGC Conduit is approved as EGC per 250.118. No wire required inside conduit (unless local AHJ mandates a pull wire for redundant grounding).
Parallel conductor runs (e.g., 400A service) Multiple raceways used per 310.10(H). Run a separate ground wire in EACH raceway, sized to the breaker per Table 250.122 (NEC 250.122(F)).

What This Chart Cannot Tell You

While the ground wire chart (Table 250.122) is the ultimate authority for branch circuits and feeders, it is frequently confused with other grounding tables. Do not use this chart for the following scenarios:

  1. Grounding Electrode Conductor (GEC): The wire connecting your main panel's neutral bar to the physical earth (ground rods, ufer ground, or metal water pipe) is not sized by Table 250.122. It is sized by NEC Table 250.66, which bases the wire size on the circular mil area of the largest ungrounded service entrance conductor, not the main breaker rating.
  2. Main Bonding Jumper: The internal connection between the neutral bus and the panel enclosure at the service disconnect is sized per NEC 250.28(D), which uses a completely different calculation table.
  3. Communications and Low Voltage: The grounding requirements for coaxial cables, ethernet, and telephone lines fall under Article 800, which typically mandates a minimum 14 AWG copper grounding conductor regardless of the main panel size.

Always verify with your local Authority Having Jurisdiction (AHJ). While the NEC provides the baseline mathematical framework, local inspectors in areas with high soil resistivity or specific municipal amendments may require upsized grounding conductors across the board. For comprehensive code updates and local amendments, consult Electrical Contractor Magazine's code section to stay current on the latest NEC adoption cycles.