The size of your equipment grounding conductor (EGC) is determined strictly by the rating of the overcurrent protective device (breaker or fuse), not the ampacity or gauge of your ungrounded (hot) conductors. If you are looking for a grounding conductor sizing chart, you need NEC Table 250.122. Find your breaker size in the left column below, and read across to your conductor material to get your minimum required AWG.
The Grounding Conductor Sizing Chart (NEC Table 250.122)
| Overcurrent Device Rating (Amps) | Copper (AWG/kcmil) | Aluminum (AWG/kcmil) |
|---|---|---|
| 15 | 14 | 12 |
| 20 | 12 | 10 |
| 30 | 10 | 8 |
| 40 | 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 kcmil |
Quick-Jump: Most Queried Residential Breaker Sizes
For standard residential branch circuits and feeders, bookmark these specific copper wire requirements:
- 15A Breaker (Lighting/Receptacles): 14 AWG Copper
- 20A Breaker (Kitchen/Bath/Laundry): 12 AWG Copper
- 30A Breaker (Dryer/Water Heater): 10 AWG Copper
- 40A Breaker (Range/Oven): 10 AWG Copper
- 50A Breaker (Hot Tub/EV Charger): 10 AWG Copper
- 60A Breaker (Subpanel/Heavy EV): 10 AWG Copper
- 100A Breaker (Subpanel Feeder): 8 AWG Copper
- 200A Breaker (Main Service/Feeder): 6 AWG Copper (Note: 4 AWG is often used in residential SER cable due to manufacturer standardization, but 6 AWG is the NEC minimum).
Which Column Applies to Your Installation?
The choice between the Copper and Aluminum columns is straightforward, but installers frequently confuse EGC rules with ungrounded conductor rules. Here is how to determine your column and application rules:
- Material Match: If your hot wires are copper, use the copper column. If your hot wires are aluminum (like SER cable for a subpanel), use the aluminum column. You are permitted to use a copper EGC with aluminum hot wires, but you cannot use an aluminum EGC with copper hot wires if it creates a dissimilar metal termination issue at the device.
- Insulation Requirements: The EGC can be bare, covered, or insulated. However, if it is insulated or covered, the outer finish must be green, or green with one or more yellow stripes (NEC 250.119).
- Temperature Ratings Do Not Apply: A common mistake is looking at the 75°C column for a 75°C rated breaker. Table 250.122 is entirely independent of the insulation temperature rating (THHN vs XHHW). A 60A breaker requires a 10 AWG copper EGC regardless of whether you pull 90°C THHN or 60°C NM-B.
The Voltage Drop Trap: How Upsizing Modifies the Base Value
This is where the table alone fails you. While standard ampacity derating (e.g., bundling four current-carrying conductors in a conduit) does not require you to upsize the EGC, upsizing your hot wires to mitigate voltage drop absolutely does.
Under NEC 250.122(B), if you increase the size of your ungrounded (hot) conductors to compensate for voltage drop, you must proportionately increase the size of the EGC based on the circular mil area of the conductors.
You are running a 60A circuit 150 feet to a subpanel. To keep voltage drop under 3%, you upsize your hot wires from the base 6 AWG (26,240 circular mils) to 4 AWG (41,740 circular mils).
1. Calculate the ratio: 41,740 / 26,240 = 1.59.
2. Find the base EGC for 60A: 10 AWG (10,380 circular mils).
3. Multiply by the ratio: 10,380 x 1.59 = 16,504 circular mils.
4. Select the new EGC: 8 AWG is 16,510 circular mils.
Result: You must pull an 8 AWG ground wire, not the 10 AWG listed in the base table.
Decision Tree: Sizing Your EGC in 4 Steps
Use this decision-tree-table to terminate your sizing process with one concrete wire pick.
| Step | Condition / Question | Action / Concrete Pick |
|---|---|---|
| 1. Identify OCPD | What is the breaker or fuse rating? | Note the exact amp rating (e.g., 50A). Do not use the wire's ampacity. |
| 2. Base Lookup | What does Table 250.122 say? | Find 50A -> Pick 10 AWG Copper (Base Pick). |
| 3. Voltage Drop Check | Did you upsize the hot wires for voltage drop? | If NO: Stop here. Buy 10 AWG Copper. If YES: Proceed to Step 4. |
| 4. Proportional Math | Calculate (Upsized Hot cmil / Base Hot cmil) x Base EGC cmil. | Match the result to the next largest standard AWG cmil in NEC Chapter 9, Table 8. Buy that specific gauge. |
What This Table Cannot Tell You
While NEC Table 250.122 covers 95% of standard residential and commercial branch circuits, it has strict boundaries. You must consult other code sections for the following edge cases:
- Parallel Raceways (NEC 250.122(F)): If you are running parallel conduits for a massive feeder (e.g., 800A service using two sets of 500 kcmil), you cannot divide the EGC. You must run a full-sized EGC in every single parallel raceway, and each one must be sized based on the total 800A OCPD rating (which would require a 1/0 AWG copper EGC in each conduit).
- Motor Circuits (NEC Article 430): Motors use inverse-time breakers that are often sized much larger than the conductor ampacity to handle inrush current. For motor circuits, the EGC is sized based on the motor branch-circuit short-circuit and ground-fault protective device rating, but it never needs to be larger than the circuit conductors themselves.
- Flexible Cords and Fixture Wires: Table 250.122 does not apply to the internal grounding wires inside manufactured flexible cords (like SJTW) or appliance fixture wires. Those are governed by UL listing standards and NEC 250.118.
- Local AHJ Overrides: Some local jurisdictions mandate a minimum 8 AWG or 6 AWG copper EGC for all residential subpanel feeders regardless of the breaker size to ensure mechanical durability and lower impedance fault paths. Always verify with your local inspector.
By anchoring your grounding strategy to the overcurrent device rating and applying the proportional math for voltage drop, you ensure a low-impedance fault path that will reliably trip the breaker during a short circuit, keeping your bench, tools, and home safe.
