Equipment Grounding Conductor Chart: NEC Table 250.122 Sizing Guide

The size of your equipment grounding conductor (EGC) is determined strictly by the rating of the overcurrent protective device (breaker or fuse) protecting the circuit, not by the ampacity of the circuit conductors themselves. Sizing this wire correctly ensures that during a ground fault, enough current flows to trip the breaker instantly, clearing the fault before a fire or shock hazard occurs.

The definitive source for this sizing is the National Electrical Code (NEC) Table 250.122. Below is the complete reference chart, followed by the critical modification rules for voltage drop and the common trapdoors that fail inspections.

The Master Equipment Grounding Conductor Chart (NEC Table 250.122)

How to read this table: Look at the rating of the breaker or fuse protecting the circuit in the first column. Follow that row to the right to find the minimum required wire size for Copper or Aluminum. Note that unlike ampacity tables (NEC 310.16), temperature ratings (60°C vs. 75°C) do not dictate the base EGC size; the breaker size is the sole determining factor for the base value. Which column applies to your installation? Use the Copper column for standard NM-B, THHN, or UF-B home wiring. Use the Aluminum column only if your ungrounded (hot) circuit conductors are aluminum, which is typically reserved for large feeders (e.g., 2-2-2-4 MHF) or heavy commercial runs.

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These are the most queried values for residential and light-commercial DIY projects:

• 15A & 20A Receptacles: 14 AWG Cu / 12 AWG Cu. (Note: While 14 AWG is legal for a 15A EGC, standard 12/2 NM-B includes a 12 AWG ground, which is perfectly fine and exceeds the minimum).
• 30A Dryer / RV Outlet: 10 AWG Cu. Matches the 10 AWG hot conductors in standard 10/3 NM-B.
• 50A Range / EVSE: 10 AWG Cu. Common trap: Many builders assume a 50A breaker requires an 8 AWG ground. The table explicitly allows 10 AWG Cu up to 60A.
• 100A Subpanel Feeder: 8 AWG Cu. If using 2-2-2-4 Aluminum SER cable, the included 4 AWG Al ground exceeds the 6 AWG Al minimum.
• 200A Main Service / Subpanel: 6 AWG Cu or 4 AWG Al.

When the Base Chart Fails: Upsizing for Voltage Drop

A frequent point of confusion is how 'derating rows' modify the base value. Unlike ampacity tables, Table 250.122 does not contain derating rows for ambient temperature or conduit fill. The EGC does not carry continuous load current, so it does not heat up under normal operation. However, the base table values are modified by a mandatory proportional upsizing rule found in OSHA and NEC Section 250.122(B).

If you must increase the size of your ungrounded (hot) conductors to compensate for voltage drop on long runs, you must proportionally increase the size of the equipment grounding conductor. You cannot use the base table value if the hot wires have been upsized.

Worked Numeric Example: 50A EV Charger at 150 Feet

You are wiring a 50A Level 2 EV charger. The base table requires 6 AWG Cu hots and a 10 AWG Cu EGC. However, at 150 feet, a 6 AWG wire will suffer excessive voltage drop. You calculate that you need to upsize the hot conductors to 4 AWG Cu to keep voltage drop under 3%.

• Base Hot (6 AWG): 26,240 circular mils (cmil)
• Upsized Hot (4 AWG): 41,740 cmil
• Base EGC (10 AWG): 10,380 cmil

The Math: 10,380 × (41,740 ÷ 26,240) = 10,380 × 1.59 = 16,504 cmil.

Looking at standard wire area charts, 8 AWG is 16,510 cmil. Therefore, your minimum EGC is now 8 AWG Cu, not the 10 AWG listed in the base chart. If you pull 4 AWG hots with a 10 AWG ground, you will fail inspection.

What This Table Cannot Tell You (Common Trapdoors)

Table 250.122 is highly specific, but it is not a universal grounding cheat sheet. Relying on it for the wrong application is the leading cause of grounding-related inspection failures.

EGC vs. GEC: The Ultimate Confusion

This chart is exclusively for the Equipment Grounding Conductor (EGC)—the wire that runs from the panel to the outlet, appliance, or subpanel to provide a low-impedance fault current path back to the source. It does not apply to the Grounding Electrode Conductor (GEC). The GEC is the wire that connects your main service panel to the physical earth (ground rods, ufer grounds, or metallic water pipes). Sizing the GEC requires an entirely different chart: NEC Table 250.66, which bases the wire size on the physical size of the largest service entrance conductor, not the breaker rating.

Parallel Conductor Runs

If you are running parallel sets of conductors (e.g., two sets of 500 kcmil per phase for a 800A feeder), Table 250.122 cannot be used by simply looking at the main breaker size. Under NEC 250.122(C), each parallel raceway or cable must contain its own EGC, and that individual EGC must be sized based on the overcurrent device rating, but it must also be run in parallel with the phase conductors in each specific conduit. You cannot run a single massive ground wire outside the parallel conduits.

The 'Next Size Up' Rule for Breakers

What if your calculated load is 45A, so you install a 50A breaker, but you use 6 AWG wire (rated 65A at 75°C)? You still use the 50A row in the table (10 AWG Cu). The table is tied to the overcurrent device rating, not the wire ampacity or the actual load. Conversely, if a specific motor circuit allows a breaker to be sized at 250% of the motor FLA (e.g., a 20A motor on a 50A breaker), NEC 250.122 Exception 1 allows you to size the EGC based on the motor's full-load current rather than the oversized breaker, provided the EGC is not smaller than the circuit conductors. Always verify if your specific load type (motor, capacitor, welder) has an exception that overrides the main chart.