What Size Ground Wire Do You Need?

The two ground wires (EGC vs GEC)

Almost every "what size ground wire" argument online is really two questions wearing one coat. There are two different ground wires, sized from two different tables:

Equipment grounding conductor (EGC) — the ground that runs with your circuit and bonds the metal so a fault trips the breaker. Sized by the breaker (NEC Table 250.122).
Grounding electrode conductor (GEC) — the wire from your panel out to the ground rods or metal water pipe. Sized by the service (NEC Table 250.66).

Get the right table for the job and the confusion disappears. The rest of this guide is a full ground wire size chart for each one, plus the rule that surprises everyone — the ground-rod wire barely grows.

Equipment ground size chart (NEC 250.122)

This is the ground inside your branch circuits and feeders — the green or bare wire. It's sized by the breaker rating, not by the wire's length:

Breaker / OCPD	Copper	Aluminum
15 A	14 AWG	12 AWG
20 A	12 AWG	10 AWG
30–60 A	10 AWG	8 AWG
100 A	8 AWG	6 AWG
200 A	6 AWG	4 AWG
300 A	4 AWG	2 AWG
400 A	3 AWG	1 AWG

One thing worth noticing: 30, 40, 50, and 60 amp circuits all share a 10 AWG copper ground — which is why every dryer, range, and small feeder in the 30–60 amp range uses the same ground wire. And in NM-B "Romex" cable the equipment ground is already inside, sized correctly, so you rarely add one on a branch circuit.

Grounding-electrode conductor chart (NEC 250.66)

This is the separate wire that connects your panel to the grounding electrodes — the driven ground rods and the metal water pipe. It's sized by your service conductor size, not the breaker:

Largest service conductor (copper)	GEC (copper)
2 AWG or smaller	8 AWG
1 or 1/0 AWG	6 AWG
2/0 or 3/0 AWG	4 AWG
Over 3/0 to 350 kcmil	2 AWG
Over 350 to 600 kcmil	1/0 AWG

So a typical 100 amp service lands on an 8 AWG electrode conductor, and a 200 amp service (around 2/0 copper) on a 4 AWG — except when it runs only to ground rods, which is where the next rule kicks in. Aluminum is allowed for the electrode conductor too, sized from the aluminum column of the same table.

Why the ground-rod wire is only 6 AWG

Here's the fact that trips people up. A grounding-electrode conductor that runs only to a ground rod or pipe electrode never has to be bigger than 6 AWG copper — even on a 200 amp service (NEC 250.66(A)). A driven rod simply can't dissipate more current than that, so a heavier wire buys nothing.

The rod-wire caps

To a ground rod / pipe electrode → never larger than 6 AWG copper (250.66(A)).
To a concrete-encased "Ufer" electrode → never larger than 4 AWG copper (250.66(B)).
That's why a big 200 amp service still runs just 6 AWG out to the rods, even though the same service would take 4 AWG to a metal water pipe.

When you have to upsize the ground

If you bump your circuit conductors up a size to fight voltage drop on a long run, the code makes you upsize the equipment ground proportionally too, by cross-sectional area (NEC 250.122(B)). It's a common miss on long feeders: people upsize the hots and leave the ground at the table value. The Voltage Drop Calculator tells you when a run needs the bump in the first place.

Copper vs aluminum grounds

Every row of the 250.122 chart has both columns, and aluminum grounds are one to two sizes larger than copper — a 200 amp circuit is 6 AWG copper or 4 AWG aluminum. Aluminum needs the usual termination care (rated lugs, anti-oxidant where required). Most branch-circuit grounds are copper; aluminum shows up mainly on larger feeders. Our AWG ampacity chart has the conductor side of this.

Do I even need to run a separate ground?

For most branch circuits, no — NM-B cable already includes a correctly-sized bare equipment ground. You pull a separate ground mainly when you wire in conduit (run a green or bare EGC with the circuit) and for the GEC to your electrodes at the service. Quick color check: green or bare = ground, white = neutral. They do different jobs — the ground normally carries no current and only comes alive during a fault.

Common grounding mistakes

The classic is sizing the ground by wire length instead of the breaker — the EGC comes straight off the OCPD rating. Close behind: using the wrong table (250.122 for the equipment ground vs 250.66 for the electrode conductor). Others: oversizing the rod wire past 6 AWG for no reason, or undersizing it; forgetting to upsize the EGC when you upsize conductors for voltage drop; and bonding neutral and ground downstream of the main (they're only bonded at the service, never in a subpanel). Grounding is inspected work, so confirm with your AHJ.

Ground wire size by common circuit

The equipment ground for the circuits people ask about most, with the full guides:

20 amp circuit → 12 AWG copper. See 20 amp wire size.
30–60 amp circuit → 10 AWG copper. See 50 amp and 60 amp wire size.
100 amp service → 8 AWG copper. See 100 amp service wire size.
200 amp service → 6 AWG copper (and 6 AWG to the rods). See 200 amp service wire size.

Frequently asked questions

Code & SafetyWhat size ground wire do I need?

It depends which ground. The equipment ground in a circuit is sized by the breaker (NEC Table 250.122) — 14 AWG for 15A, 12 AWG for 20A, 10 AWG for 30–60A, 8 AWG for 100A, 6 AWG for 200A. The wire to your ground rods is sized by the service (Table 250.66) but caps at 6 AWG copper.

⚡ Wire Size calculator →

Code & SafetyWhat size equipment ground for a 20 amp circuit?

12 AWG copper (or 10 AWG aluminum) per NEC Table 250.122. In NM-B cable this ground is already included and sized correctly.

Code & SafetyWhat size ground wire for a 100 amp service?

The equipment ground for a 100 amp feeder is 8 AWG copper (250.122). The grounding-electrode conductor to the rods or water pipe is also 8 AWG copper for a typical 100 amp service (250.66).

Code & SafetyWhat size ground wire for a 200 amp service?

The equipment ground for a 200 amp feeder is 6 AWG copper (250.122). The electrode conductor is 4 AWG copper to a water pipe, but only 6 AWG copper to ground rods, because 250.66(A) caps the rod wire at 6 AWG.

Code & SafetyWhat size wire to a ground rod?

6 AWG copper is the most you ever need to a driven ground rod, because NEC 250.66(A) says the rod conductor need not be larger than 6 AWG — even on a 200 amp service.

Code & SafetyIs the ground wire the same size as the hot wire?

Usually no. The equipment ground is sized from the breaker rating in Table 250.122 and is typically smaller than the hot conductors — for example a 50 amp circuit uses 6 AWG hots but only a 10 AWG ground.

Wire & CircuitDo I need a separate ground wire?

Not with NM-B cable — the bare equipment ground is already inside and sized correctly. You run a separate ground when wiring in conduit, and for the grounding-electrode conductor to the rods at the service.

Code & SafetyDo I upsize the ground when I upsize for voltage drop?

Yes. If you increase the circuit conductors for voltage drop, NEC 250.122(B) requires you to increase the equipment grounding conductor proportionally by cross-sectional area.

Dr. Artie Vance

Technical reviewer · Ph.D. in Physics, MIT · 14 years' experience · Cross-checked against NEC 2026 & 2026

This guide is for general information based on the National Electrical Code. Grounding and bonding rules vary by NEC edition and your local authority having jurisdiction (AHJ), and are inspected work. Electrical work can be dangerous, so when in doubt, hire a licensed electrician.