What size ground wire for a 200 amp service?

That depends on which ground you mean. The grounding electrode conductor to the rods or Ufer is sized from the service conductors under Table 250.66: a 200 A dwelling service on 2/0 copper or 4/0 aluminum needs 4 AWG copper. If the only electrodes are ground rods, the conductor to the rods never has to exceed 6 AWG copper (NEC 250.66(A)). A 200 A feeder to a subpanel instead needs a 6 AWG copper equipment ground (Table 250.122).

Why is the ground wire smaller than the hot wires?

The equipment ground only carries current for the fraction of a second it takes a fault to trip the breaker, so it is sized to survive that fault, not to carry the load all day. That is why Table 250.122 keys off the breaker rating rather than the load, and why a 50 A circuit on 6 AWG hots can use a 10 AWG copper ground.

What size ground wire for a 50 amp circuit?

10 AWG copper or 8 AWG aluminum. A 50 A breaker falls in Table 250.122's 60 A row, which covers everything from 21 A to 60 A. The same 10 AWG copper ground serves 30 A, 40 A, 50 A and 60 A circuits.

Ground wire size chart

Two different NEC tables answer “what size ground wire”: the ground that runs with a circuit is sized by its breaker, and the ground to the rods is sized by the service conductors. Both are below, copper and aluminum.

Ground wire for common circuits

Equipment grounding conductor (the bare or green wire) by breaker size, from NEC Table 250.122.

Breaker	Copper ground	Aluminum ground	Typical use
15 A	14 AWG	12 AWG	Lighting, general outlets
20 A	12 AWG	10 AWG	Kitchen, bath, garage outlets
30 A	10 AWG	8 AWG	Dryer, water heater
40 A	10 AWG	8 AWG	Range, 32 A EV charger
50 A	10 AWG	8 AWG	Range, NEMA 14-50, 40 A EV charger
60 A	10 AWG	8 AWG	48 A EV charger, subpanel
70 A	8 AWG	6 AWG	Subpanel, heat pump
100 A	8 AWG	6 AWG	Subpanel feeder
125 A	6 AWG	4 AWG	Large subpanel feeder
200 A	6 AWG	4 AWG	200 A feeder

Equipment grounding conductor (NEC Table 250.122)

Find the first row at or above your breaker or fuse rating — a 30 A breaker uses the 60 A row.

Breaker or fuse, not exceeding	Copper	Aluminum or copper-clad Al
15 A	14 AWG	12 AWG
20 A	12 AWG	10 AWG
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
500 A	2 AWG	1/0 AWG
600 A	1 AWG	2/0 AWG
800 A	1/0 AWG	3/0 AWG
1,000 A	2/0 AWG	4/0 AWG
1,200 A	3/0 AWG	250 kcmil
1,600 A	4/0 AWG	350 kcmil
2,000 A	250 kcmil	400 kcmil
2,500 A	350 kcmil	600 kcmil
3,000 A	400 kcmil	600 kcmil

Shown to 3,000 A; the code table continues to 6,000 A for large commercial and industrial services.

Upsized the hots for voltage drop? Upsize the ground too

NEC 250.122(B): when the hot conductors are made larger than the minimum to cut voltage drop on a long run, the equipment ground must grow by the same ratio of circular-mil area. Most charts skip this rule, and it is the one that catches long subpanel and detached-garage feeders.

Example: a 50 A feeder would normally use 8 AWG copper hots (16,510 circular mils) with a 10 AWG copper ground (10,380 cmil). Over a long run you step the hots up to 6 AWG (26,240 cmil), a factor of 1.59. The ground must then be at least 10,380 × 1.59 = 16,500 cmil, which is 8 AWG copper, not 10.

The ground never has to be larger than the circuit's own hot conductors (NEC 250.122(A)). Circular-mil areas are from NEC Chapter 9, Table 8. Check a run with the voltage drop calculator.

Grounding electrode conductor (NEC Table 250.66)

The wire from the service equipment to the ground rods, concrete-encased (Ufer) electrode or water pipe. Sized by the largest hot service-entrance conductor, not the breaker.

Service conductor, copper	Service conductor, aluminum	Copper GEC	Aluminum GEC
2 AWG or smaller	1/0 AWG or smaller	8 AWG	6 AWG
1 or 1/0 AWG	2/0 or 3/0 AWG	6 AWG	4 AWG
2/0 or 3/0 AWG	4/0 AWG or 250 kcmil	4 AWG	2 AWG
Over 3/0 AWG – 350 kcmil	Over 250 – 500 kcmil	2 AWG	1/0 AWG
Over 350 – 600 kcmil	Over 500 – 900 kcmil	1/0 AWG	3/0 AWG
Over 600 – 1100 kcmil	Over 900 – 1750 kcmil	2/0 AWG	4/0 AWG
Over 1100 kcmil	Over 1750 kcmil	3/0 AWG	250 kcmil

A typical 200 A dwelling service on 2/0 copper or 4/0 aluminum needs a 4 AWG copper grounding electrode conductor.
To ground rods, pipe or plate electrodes alone, the conductor never has to be larger than 6 AWG copper or 4 AWG aluminum (NEC 250.66(A)).
To a concrete-encased (Ufer) electrode alone, it never has to be larger than 4 AWG copper (NEC 250.66(B)).

Notes

Values are code minimums from the 2023 NEC. Your jurisdiction may have adopted an earlier edition or local amendments.
Table 250.122 is a floor: the ground must also be large enough to clear a fault quickly (NEC 250.4), which can call for a larger conductor on very long runs.
Grounding and bonding errors are a shock and fire hazard. Have a licensed electrician do the work and pull the permit, and confirm with your local authority having jurisdiction (AHJ).

Frequently asked questions

8 AWG copper or 6 AWG aluminum. NEC Table 250.122 sizes the equipment grounding conductor by the breaker protecting the feeder, and the 100 A row calls for 8 AWG copper. If the feeder conductors were upsized for voltage drop on a long run, the ground has to be upsized in proportion (NEC 250.122(B)).