The correct size for a branch circuit equipment grounding conductor (EGC) is determined strictly by the rating of the overcurrent protective device (OCPD)—the breaker or fuse—not the ungrounded wire size or the actual load current. If you are installing a 50A continuous load on a 70A breaker, you size the EGC for 70A. This grounding chart and decision framework will get you the exact AWG or kcmil requirement, handle voltage-drop upsizing, and keep you out of the inspector's crosshairs.

The NEC Table 250.122 Grounding Chart (Copper & Aluminum)

This table is sourced directly from NFPA 70 (National Electrical Code) Table 250.122.

How to read this table: Look at the first column to find the rating of your breaker or fuse (OCPD). Move right to select either the Copper or Aluminum column. The temperature rating of the conductor insulation (e.g., THHN at 90°C vs. THW at 75°C) does not change the minimum EGC size; the chart is strictly tied to the OCPD rating.

Bookmark Quick-Jumps: The most queried residential and light-commercial values are 20A (12 AWG Cu), 60A (10 AWG Cu), 100A (8 AWG Cu), and 200A (6 AWG Cu).

NEC Table 250.122 Minimum Size Equipment Grounding Conductors
OCPD Rating (Amps) Copper (AWG/kcmil) Aluminum (AWG/kcmil)
151412
201210
30108
40108
60108
10086
20064
30042
40031
50021/0
60012/0
8001/03/0
10002/04/0
12003/0250 kcmil

Decision Path: Sizing Your Equipment Grounding Conductor

Use this decision tree to terminate your sizing process with a single, concrete part pick. Never guess; follow the logic path based on your specific installation parameters.

Installation Condition Required Action Concrete Result / Pick
Standard residential branch circuit (e.g., 20A receptacle circuit, <100 ft run). Read base chart for OCPD rating. Pick: 12 AWG Bare Copper.
Heavy continuous load requiring OCPD upsizing (e.g., 40A EV charger requires 125% sizing = 50A breaker). Use the *breaker* rating (50A), not the load rating (40A). Chart jumps from 40A to 60A row. Pick: 10 AWG Bare Copper (Sized for the 60A breaker).
Long feeder run where ungrounded conductors are upsized strictly to mitigate voltage drop. Apply NEC 250.122(B) proportional upsizing math (see next section). Pick: Calculated upsized AWG (e.g., 8 AWG instead of 10 AWG).
Parallel conductor installation (e.g., two sets of 500 kcmil per phase on a 800A service). Size a full EGC for the main OCPD, then run one in *each* parallel raceway. Do not split the EGC. Pick: Two separate 1/0 AWG Copper wires (One per conduit).

The Voltage Drop Catch: Proportional Upsizing (NEC 250.122(B))

The most common way DIYers and junior electricians fail an inspection is by ignoring NEC 250.122(B). If you increase the size of your ungrounded (hot) conductors to compensate for voltage drop over a long distance, you must proportionally increase the size of your EGC.

The math relies on circular mils (cmil). Here is a worked bench example:

  1. The Base Setup: You have a 100A breaker feeding a subpanel 200 feet away. Table 250.122 dictates an 8 AWG Copper EGC. Standard ungrounded wire for 100A is 3 AWG Copper.
  2. The Upsize: To keep voltage drop under 3%, you upsize the ungrounded conductors from 3 AWG to 1 AWG Copper.
  3. The Ratio: According to Copper Development Association wire data, 1 AWG is 83,690 cmil. 3 AWG is 52,620 cmil. The ratio is 83,690 / 52,620 = 1.59.
  4. The EGC Adjustment: Base 8 AWG EGC is 16,510 cmil. Multiply by the ratio: 16,510 × 1.59 = 26,250 cmil.
  5. The Final Pick: The next standard wire size up that meets or exceeds 26,250 cmil is 6 AWG (26,240 cmil is slightly under, so we must jump to 4 AWG which is 41,740 cmil, or accept 6 AWG if local AHJ allows the 0.03% variance. To be strictly code-compliant without arguments, jump to 4 AWG Copper).
Bench Tip: Don't rely on mental math for cmil ratios on the jobsite. Use a dedicated NEC voltage drop calculator app that includes a 250.122(B) EGC output field. It saves you from buying a 500ft spool of the wrong ground wire.

What This Grounding Chart Cannot Tell You

Table 250.122 is exclusively for Equipment Grounding Conductors (EGCs)—the wires that clear faults on branch circuits and feeders by tripping the breaker. It does not cover the following, which require entirely different tables and physics:

  • Grounding Electrode Conductors (GEC): The wire connecting your main panel to the ground rods or ufer ground. This is sized via NEC Table 250.66, based on the size of the largest ungrounded service entrance conductor, not the breaker.
  • Main System Bonding Jumpers: The connection between the grounded neutral and the equipment ground at the main disconnect. Sized via NEC 250.28.
  • Equipotential Bonding: Pool shells, hot tubs, and agricultural buildings require specific bonding grids (NEC Article 680 and 547) that rely on structural steel and buried wire loops, not standard EGC charts.
  • Conduit as EGC: While rigid metal conduit (RMC) and EMT can legally serve as the EGC in many commercial applications (NEC 250.118), residential best practice and many local AHJs mandate a dedicated wire EGC pulled inside the raceway to ensure fault-clearing continuity if a coupling vibrates loose over time.

Field Verification and Termination Specs

Sizing the wire correctly is only half the battle; terminating it correctly ensures it actually clears a fault before the wire melts. When terminating your EGC at the panel or subpanel:

  1. Strip Length: Strip exactly 3/4 inch of insulation (if using THHN/THWN) or leave bare wire as-is. Do not nick the copper strands; a nicked 10 AWG ground can snap under the thermal stress of a 60A fault current.
  2. Torque: Use a calibrated torque screwdriver. For standard 10-14 AWG grounds on a residential ground bar, the typical torque spec is 20 to 25 in-lbs (always verify the stamp on the specific panel label, e.g., Square D QO or Siemens EQ).
  3. One Wire, One Lug: NEC 110.14(A) and panel listings dictate that you cannot land two EGCs under a single screw terminal unless the lug is explicitly rated for two wires. Buy a $15 ground bar extension kit if you run out of holes; do not double-lug grounds.
  4. Pigtailing: If you are extending an existing circuit and need to splice an EGC in a junction box, use a properly sized wire nut (e.g., a red Ideal WireNut for up to three 10 AWG solids) or a Wago 221-613 lever nut. Never leave a ground wire floating or capped off alone in a box.

By anchoring your EGC sizing strictly to the OCPD rating and applying proportional math only when voltage drop demands it, you will pull the exact right wire every time. Keep Table 250.122 bookmarked, verify your terminations with a torque driver, and let the physics do the work.