Ground Wire Size Chart: EGC (250.122) & GEC (250.66)

NEC 250 · Grounding · Updated 2026-08-07

A ground wire size chart answers two different questions, and mixing them up is the most common grounding mistake in the field. The equipment grounding conductor (EGC) that runs with your circuit is sized from the breaker ahead of it under NEC 250.122: a 15 A breaker needs 14 AWG copper, 20 A needs 12 AWG, 30 to 60 A needs 10 AWG, 70 to 100 A needs 8 AWG, and 110 to 200 A needs 6 AWG.

The grounding electrode conductor (GEC) that ties your service to the ground rods or building steel follows a completely different rule, NEC 250.66, and is sized from the service entrance conductors instead of any breaker. This guide gives you the full copper EGC chart, explains how the GEC differs, works a voltage drop upsizing example under 250.122(B), and covers the conduit fill and box fill questions that follow the ground wire onto the job.

Copper Ground Wire Size Chart (NEC 250.122)

The table below is the chart most people searching for ground wire size actually need: the minimum copper equipment grounding conductor for a circuit, based on the rating of the breaker or fuse protecting that circuit. It comes straight from NEC 250.122. The EGC carries no load current in normal operation; its whole job is to give fault current a low impedance path back to the source so the breaker trips fast. That is why it is sized from the overcurrent device, not from the load or the wire.

Three notes on reading the chart. First, the EGC tracks the breaker, so a 40 A, a 50 A, and a 60 A circuit all use the same 10 AWG copper EGC even though their circuit conductors differ. Second, these are copper sizes; aluminum EGCs are larger for the same rating and come from the aluminum column of the same NEC table. Third, this chart is a minimum. A long run that gets upsized for voltage drop drags the EGC up with it, which is worked out below.

EGC, GEC, or Neutral: Know Which Wire You Are Sizing

Three different conductors get called the ground wire on job sites, and they follow three different rules. Sizing one of them from the other's chart is a red tag waiting to happen.

• Equipment grounding conductor (EGC): the bare or green wire that runs with the circuit conductors from the panel to every box, device, and enclosure. Sized from the breaker per NEC 250.122 using the chart above.
• Grounding electrode conductor (GEC): the wire from the service to the grounding electrode system, meaning ground rods, a concrete encased electrode, a metal water pipe, or building steel. Sized from the service entrance conductors per NEC 250.66.
• Grounded conductor (neutral): the white current carrying conductor. It is not a ground wire at all, even though it lands on the same bar as the grounds at the service. It is sized for load like any circuit conductor; the wire size chart covers that.

If your question is what size ground goes in the pipe with my circuit, you want the EGC chart above. If your question is what size wire goes to my ground rods, you want 250.66, covered next.

Sizing the GEC Under NEC 250.66

The GEC is sized from the largest ungrounded service entrance conductor, not from the main breaker. That distinction matters because services are often wired with conductors that do not line up neatly with the breaker handle, and 250.66 keys off the actual copper or aluminum conductor size feeding the service. Look the value up in Table 250.66 in the code book against your real service conductors rather than guessing from the main breaker rating.

Two practical points. First, 250.66 contains its own allowances for conductors that run only to certain electrode types, such as a ground rod or a concrete encased electrode, which is why you often see a smaller GEC landing on a rod than the base table would suggest. Read those provisions in the book before buying wire. Second, the GEC is a one time, service level conductor. Upsizing branch circuits for voltage drop, adding circuits, or derating conductors in a hot ceiling has no effect on the GEC; those adjustments act on circuit conductors and their EGCs instead.

EGC vs Circuit Conductor: When They Stop Matching

On small branch circuits the ground is the same size as the circuit conductors, which is why common cable assemblies feel natural: 14 AWG conductors with a 14 AWG ground on a 15 A breaker, 12 with 12 on a 20 A, 10 with 10 on a 30 A. Above 30 A the two curves split, and the EGC is allowed to be smaller than the conductors it protects. The table shows the split using the copper 75 C ampacities from NEC 310.16 and the small conductor caps in 240.4(D).

The gap keeps widening as circuits grow: a 100 A feeder needs only an 8 AWG copper EGC, and a 200 A feeder only a 6 AWG. That looks wrong to a lot of people the first time they see it, but the EGC only has to carry fault current for the fraction of a second it takes the breaker to open, not continuous load. Pick the circuit conductors from the wire size chart, apply any adjustment factors from the conduit derating guide, then read the EGC straight off 250.122.

Worked Example: Voltage Drop Upsizing and 250.122(B)

When you upsize circuit conductors for voltage drop, NEC 250.122(B) requires the EGC to grow in proportion to the circular mil increase. Here is the whole calculation for a realistic circuit, with every number shown.

1. Start with the base circuit: A 20 A, 120 V branch circuit runs 100 ft one way to a 12 A load. The base wire is 12 AWG copper (6530 circular mils) with a 12 AWG copper EGC per 250.122.
2. Check voltage drop on 12 AWG: Single phase voltage drop is VD = (2 x K x I x L) / CM, with K = 12.9 for copper. VD = (2 x 12.9 x 12 x 100) / 6530 = 30,960 / 6530 = 4.74 V. That is 4.74 / 120 = 3.95 percent, over the 3 percent recommendation, so the run gets upsized. The formula is broken down fully in the voltage drop guide.
3. Recheck on 10 AWG: 10 AWG copper is 10,380 circular mils. VD = 30,960 / 10,380 = 2.98 V, which works out to 2.49 percent of 120 V. That is under 3 percent, so 10 AWG works for the circuit conductors.
4. Upsize the EGC to match: The circuit conductors grew from 6530 to 10,380 circular mils. Under 250.122(B) the EGC must grow by the same ratio: 6530 x (10,380 / 6530) = 10,380 circular mils, which is exactly 10 AWG. The finished pull is a 10 AWG hot, a 10 AWG neutral, and a 10 AWG ground, not 10 AWG conductors over a 12 AWG ground.

The shortcut worth memorizing: on small branch circuits, where the EGC starts out equal to the circuit conductors, a one size bump in the hots lands the EGC on that same new size, because the proportion carries straight through. On larger feeders, where the EGC starts smaller than the phase conductors, run the circular mil ratio for real instead of guessing.

Can Metal Conduit Be the Ground?

Yes, where the raceway is installed as a complete system. EMT, IMC, and rigid metal conduit are recognized as equipment grounding conductors when every coupling, connector, and locknut in the run is made up tight, so a compliant metal raceway can provide the fault path without a wire EGC. In practice, many job specs and many electricians pull a wire EGC anyway: set screw fittings loosen, raceways get separated during remodels, and a green wire removes the argument entirely. If you do rely on the raceway, the rest of the raceway rules still apply, including the 360 degree limit on total bends between pull points; see how to bend EMT for the field side of that.

Ground Wires in Conduit Fill and Box Fill

A wire EGC is a real conductor with real cross section, and it counts toward raceway fill exactly like the hots and the neutral. NEC Chapter 9, Table 1 limits three or more conductors to 40 percent of the conduit's internal area, and the ground eats into that area even though it carries no load; check your counts against the conduit fill chart before committing to a pipe size. The one place the EGC gives you a break is derating: it is not a current carrying conductor, so it does not count toward the conductor count that triggers the 80, 70, and 50 percent adjustment factors of 310.15(C)(1).

Box fill treats grounds with a special rule under NEC 314.16: all the equipment grounding conductors in a box together count as one volume allowance, taken at the largest EGC present. A box with four 12 AWG grounds spliced together adds a single 2.25 cu in allowance, not four. The full counting method, with worked boxes, is in the box fill guide.

Common Ground Wire Mistakes

• Sizing the EGC from the wire instead of the breaker. A 60 A circuit wired in 6 AWG copper still needs only a 10 AWG copper EGC, because 250.122 keys off the overcurrent device.
• Using the EGC chart for the ground rods. The conductor to the electrode system is a GEC under 250.66 and is sized from the service entrance conductors, not from any breaker rating.
• Forgetting 250.122(B) after a voltage drop upsize. If the hots grew for voltage drop, the ground grows proportionally with them. Inspectors look for this on long runs.
• Bonding neutrals and grounds together in a subpanel. Downstream of the service, grounds and neutrals stay separate. The size chart is only half the job; where the wire lands matters just as much.
• Ignoring the ground in fill math. The EGC takes up conduit area and a box fill allowance, and skipping it is how a compliant looking pull ends up over the 40 percent limit.

Ground sizing on your phone, in the field. Conduit Fill & Bending Calc by Panda Taps puts the 250.122 EGC table, conduit fill for every common raceway and conductor, box fill allowances, voltage drop, and ampacity with derating in one iPhone and iPad app. It works offline with no account, so the numbers are there in the mechanical room where the question actually comes up. Download Conduit Fill & Bending Calc on the App Store.

Frequently asked questions

What size ground wire do I need for a 100 amp breaker?

A circuit or feeder protected at 100 A needs an 8 AWG copper equipment grounding conductor per NEC 250.122. If you mean the wire to the ground rods for a 100 A service, that is a grounding electrode conductor sized from the service entrance conductors under NEC 250.66 instead.

What size ground wire does a 20 amp circuit need?

A 20 A breaker requires a 12 AWG copper equipment grounding conductor. That matches the 12 AWG circuit conductors, which is why 20 A cable assemblies include a 12 AWG ground.

Is the ground wire always the same size as the hot wire?

Only on circuits up to 30 A. Above that the EGC may be smaller than the circuit conductors, so a 60 A circuit in 6 AWG copper needs only a 10 AWG ground, and a 200 A feeder needs only a 6 AWG copper ground.

Does EMT count as a ground wire?

Metal conduit such as EMT can serve as the equipment grounding conductor when it is installed as a complete system with every fitting made up tight. Many jobs still pull a wire EGC for reliability, and some specifications require one in every raceway.

Keep reading

• Wire Size & Ampacity Chart (NEC 310.16)
• Voltage Drop: the Formula, the 3% Rule, and Worked Examples
• Box Fill Calculation Explained (NEC 314.16)