The size of your equipment grounding conductor (EGC) is dictated strictly by the rating or setting of the overcurrent protective device (OCPD) ahead of the equipment, not by the ampacity of the circuit conductors. Per the National Electrical Code (NFPA 70), you must use NEC Table 250.122 to find the minimum allowable size. For a standard 20-amp residential branch circuit, the minimum EGC is 12 AWG copper. For a 60-amp subpanel feeder, it is 10 AWG copper.
The NEC Equipment Grounding Conductor Table (Table 250.122)
Before pulling wire, you need to know how to read this specific table. Unlike the ampacity tables in NEC 310.16, temperature ratings (60°C, 75°C, 90°C) do not apply to the EGC table. The EGC does not carry continuous load current under normal operation; it only carries fault current. Therefore, you ignore the insulation temperature column entirely. You look solely at the rating of the breaker or fuse protecting the circuit, then move across to the Copper or Aluminum column based on the wire material you are pulling.
| OCPD Rating or Setting (Amperes) | Size (AWG or kcmil) - Copper | Size (AWG or kcmil) - Aluminum / Copper-Clad Al |
|---|---|---|
| 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 |
| 250 | 4 | 2 |
| 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 |
| 1600 | 4/0 | 350 |
| 2000 | 250 | 400 |
| 2500 | 350 | 600 |
| 3000 | 400 | 600 |
| 4000 | 500 | 800 |
| 5000 | 700 | 1200 |
| 6000 | 800 | 1200 |
Quick-Jump Reference: Most Common Residential & Commercial Sizes
For field electricians and DIYers bookmarking this page, here are the most frequently queried rows for standard residential panels, subpanels, and heavy appliance circuits. Keep in mind these are minimums; you can always pull a larger ground wire, but never a smaller one.
- 15A / 20A Receptacle Circuits: 14 AWG / 12 AWG Copper (Typically pulled as part of standard 14/2 or 12/2 NM-B Romex).
- 30A Dryer / RV Receptacle: 10 AWG Copper (Included in 10/3 NM-B).
- 50A Range / Welder Outlet: 10 AWG Copper. (Note: Many 50A appliances use 6 AWG ungrounded conductors, but the ground only needs to be 10 AWG per the table).
- 60A Subpanel Feeder: 10 AWG Copper (Often paired with 6 AWG THHN ungrounded conductors).
- 100A Subpanel Feeder: 8 AWG Copper (Paired with 3 AWG or 2 AWG THHN/Aluminum).
- 200A Main Service / Subpanel: 6 AWG Copper or 4 AWG Aluminum.
Decision Path: Sizing Your EGC in the Field
Use this decision tree to terminate your sizing process with a concrete pick. Do not guess; follow the logic path based on your specific installation parameters.
| Installation Scenario | Condition | Concrete Action / Pick |
|---|---|---|
| Standard Branch Circuit or Feeder | Wire size matches standard ampacity requirements; no voltage drop upsizing. | Pick the exact AWG from Table 250.122 based on the breaker size. |
| Long Feeder / Voltage Drop Mitigation | Ungrounded conductors were upsized (e.g., bumped from 6 AWG to 4 AWG to prevent voltage drop over a long run). | You MUST proportionally increase the EGC per NEC 250.122(B). Calculate the circular mil ratio and apply it to the base EGC. (See math example below). |
| Using Metal Conduit (EMT, RMC, IMC) | The raceway is continuous, properly bonded, and terminates in listed fittings. | The metal raceway itself qualifies as the EGC per NEC 250.118. You do not need to pull a separate wire, though pulling a wire is considered best practice for high-reliability circuits. |
| Motor Circuits | The circuit is protected by a specific motor overload relay rather than a standard thermal-magnetic breaker. | Size the EGC based on the motor branch-circuit short-circuit and ground-fault protective device rating, not the overload relay setting (NEC Article 430). |
How Conductor Upsizing Modifies the Base EGC Value
A common point of confusion among apprentices and DIYers is how derating and adjustment factors affect the equipment ground. Here is the definitive rule: Ambient temperature correction and conduit fill derating (NEC 310.15) do not require you to increase the EGC size. The EGC table has no derating rows because the ground wire does not carry operational load current and therefore does not contribute to conduit heat buildup.
However, voltage drop upsizing absolutely does modify the base EGC value. Under NEC 250.122(B), if you increase the size of your ungrounded (hot) conductors to compensate for voltage drop, the equipment grounding conductor must be increased proportionally according to the circular mil area of the wires.
1. Calculate the ratio: 41,740 / 26,240 = 1.59.
2. Find the base EGC for 60A in Table 250.122: 10 AWG (10,380 circular mils).
3. Multiply the base EGC by the ratio: 10,380 x 1.59 = 16,504 circular mils.
4. Select the next standard wire size that meets or exceeds 16,504 cmil: 8 AWG (16,510 cmil).
Your final pull is two 4 AWG hots, one 4 AWG neutral, and one 8 AWG equipment ground.
What This Table Cannot Tell You (And Where to Look Instead)
While Table 250.122 is the bible for equipment grounding, it is strictly limited to fault-current paths back to the source. It will not give you the correct wire size for the following scenarios. If you are working on these systems, you must reference different articles to ensure your installation passes inspection and remains safe.
- Grounding Electrode Conductors (GEC): If you are bonding your panel to a ground rod, metal water pipe, or concrete-encased electrode (Ufer), you are not pulling an EGC; you are pulling a GEC. Table 250.122 does not apply here. You must use NEC Table 250.66, which sizes the GEC based on the size of the largest ungrounded service entrance conductor, not the breaker size.
- Equipment Bonding Jumpers: If you are bonding a metal outlet box to a metal conduit using a wire jumper rather than a locknut/bushing, the sizing rules shift slightly. While often matching the EGC, specific bonding jumper requirements are detailed in NEC 250.102, particularly for service-side bonding where fault currents are vastly higher than branch-circuit levels.
- Paralleled Feeders: If you are running multiple sets of conductors in parallel (e.g., two sets of 500 kcmil for an 800A service), you cannot simply look up 800A on the table and pull one massive ground wire. Per NEC 250.122(F), you must run a separate EGC in each parallel raceway, and each individual EGC must be sized based on the OCPD rating (meaning each raceway gets the full 1/0 AWG copper ground required for an 800A breaker).
For deeper code analysis and real-world inspection scenarios, resources like EC&M's National Electrical Code hub provide excellent visual breakdowns of how local Authorities Having Jurisdiction (AHJ) interpret these specific grounding and bonding tables in the field. Always verify your final wire picks against your local municipal amendments, as some jurisdictions mandate a full-size ground wire (matching the hot conductors) for all feeders regardless of what Table 250.122 permits.
