The NEC grounding conductor table (officially NEC Table 250.122) dictates the minimum size for an Equipment Grounding Conductor (EGC). The golden rule of grounding is often misunderstood: EGC size is determined strictly by the ampere rating of the overcurrent protective device (breaker or fuse), NOT the load current or the size of the ungrounded (hot) wires. If you are running a 60A breaker, your minimum copper EGC is 10 AWG, regardless of whether your hot wires are 6 AWG, 4 AWG, or 3 AWG. This table ensures the ground wire can survive the thermal and magnetic forces of a short circuit long enough for the breaker to trip.
How to Read the NEC Table 250.122 (EGC Sizing)
Before pulling wire, you need to understand how the columns in NEC 70 (National Electrical Code) Table 250.122 are structured. Unlike standard wire ampacity tables (like NEC 310.16), this table does not use 60°C or 75°C temperature columns. The sizing is based purely on the physical cross-sectional area required to handle fault current without melting.
Column Breakdown:
- Column 1 (OCPD Rating): The ampere rating of the circuit breaker or fuse protecting the circuit.
- Column 2 (Copper): The minimum AWG or kcmil size if you are using copper wire (the standard for almost all residential and light commercial branch circuits).
- Column 3 (Aluminum): The minimum size if using aluminum or copper-clad aluminum (common in heavy feeders).
The Complete NEC Grounding Conductor Table
Below is the complete reference chart for standard residential and commercial breaker sizes. Use the quick-jump links to bookmark your most common installations.
- Jump to 20A (Standard Receptacles)
- Jump to 30A (Dryers / RV Outlets)
- Jump to 50A (Ranges / EV Chargers)
- Jump to 100A (Subpanels)
- Jump to 200A (Main Service)
| OCPD Rating (Amps) | Copper EGC (AWG/kcmil) | Aluminum EGC (AWG/kcmil) |
|---|---|---|
| 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 |
Source: NEC Table 250.122 (2020/2023 Editions). For breakers rated over 400A, refer to the kcmil values in the full NEC text.
Decision Path: Sizing Your Equipment Grounding Conductor
Use this decision tree to lock in your exact wire pick without second-guessing the code. This framework terminates in a concrete material and size selection.
| Condition / Scenario | Action / Rule | Concrete Pick (Example) |
|---|---|---|
| Standard branch circuit, no voltage drop issues. | Use Table 250.122 base value for Copper. | 50A Breaker → 10 AWG Copper |
| Long run requiring ungrounded wire upsizing for voltage drop. | Apply Table 250.122(B) proportional increase (see math below). | 60A Breaker, 6 AWG upsized to 4 AWG → 8 AWG Copper |
| Parallel conductor installation (multiple raceways). | Size EGC in EACH raceway based on the OCPD rating, not the split load. | 400A Breaker, 2 parallel runs → 3 AWG Copper in EACH conduit |
| Using NM-B (Romex) cable instead of THHN in conduit. | The bare wire inside NM-B is pre-sized to meet 250.122 for the cable's rated ampacity. | 12/2 NM-B (20A capable) → Bare 12 AWG included in jacket |
When Derating Modifies the Base Value (Table 250.122(B))
The most common mistake on the jobsite is forgetting to upsize the ground wire when the hot wires are upsized for voltage drop. NEC 250.122(B) states that if ungrounded conductors are increased in size, the EGC must be increased proportionately based on the circular mil (cmil) area.
Worked Numeric Example:
You are installing a 60A EV charger 150 feet from the panel. To keep voltage drop under 3%, you upsize your ungrounded (hot) wires from the standard 6 AWG to 4 AWG copper.
- Find the base cmil: 6 AWG = 26,240 cmil. Standard 60A EGC is 10 AWG = 10,380 cmil.
- Find the new cmil: 4 AWG = 41,740 cmil.
- Calculate the ratio: 41,740 / 26,240 = 1.59.
- Apply ratio to EGC: 10,380 cmil × 1.59 = 16,504 cmil.
- Select new EGC: Look at NEC Chapter 9, Table 8. 8 AWG is 16,510 cmil. Therefore, your new minimum EGC is 8 AWG Copper.
If you had simply pulled a 10 AWG ground with those 4 AWG hots, you would fail inspection and risk the ground wire burning open during a fault before the 60A breaker trips.
What This Table Cannot Tell You (And Where to Look)
Table 250.122 is exclusively for the Equipment Grounding Conductor (the green or bare wire running alongside your circuit conductors to ground the metal enclosures and appliances). It is frequently confused with other grounding tables in NEC Article 250. Here is what this table does not cover:
- Grounding Electrode Conductor (GEC): If you are running the wire from your main service panel to the ground rod, metal water pipe, or ufer ground, you do NOT use Table 250.122. You must use NEC Table 250.66, which sizes the GEC based on the size of the largest ungrounded service entrance conductor.
- Main Bonding Jumper: The wire or busbar connecting the neutral bar to the ground bar inside the main service disconnect is sized via NEC Table 250.102(C)(1).
- Equipment Bonding Jumpers: Short jumpers used to bond metal conduit fittings or flexible metal conduit to the EGC are sized via NEC Table 250.102(C)(1), not 250.122.
When in doubt, trace the fault current path. If the wire is carrying fault current back to the breaker to trip it (EGC), use Table 250.122. If the wire is connecting the electrical system to the physical earth (GEC), use Table 250.66. Always verify your final design against your local Authority Having Jurisdiction (AHJ), as local amendments can supersede baseline NEC tables.
