Preliminary numbers for estimating and for checking a quote or a plan. The NEC edition your local authority having jurisdiction adopted comes first. A licensed electrician sizes and installs the circuit.

Maintained by BuildSolver · Updated October 19, 2026

Calculator · Electrical

Equipment grounding conductor size calculator

A 200 A breaker takes a 6 AWG copper ground wire from Table 250.122, or 4 AWG aluminum. If the feeder wire is made larger for voltage drop, 3/0 AWG replaced by 250 kcmil, the ground wire grows with it by circular mil area, to 4 AWG copper (250.122(B)). This page reads the table for any breaker from 10 to 6,000 A and works that increase. It sizes the ground wire that runs with the circuit, not the grounding electrode conductor at the service, which is sized from the service wires. To see whether the circuit wire needs to go up in the first place, use the voltage drop calculator.

Enter the rating of the breaker or fuse ahead of the circuit, and pick copper or aluminum for the ground wire.
If the circuit wire was made larger, for voltage drop for example, pick the smallest size that carries the load and the size you are installing. Leave both as not entered if it was not.
The result shows the minimum from Table 250.122, the ratio of the increase, and the ground wire size to install, held to the circuit wire size where the code allows.

The wire-type equipment grounding conductor for one circuit or feeder, by the rating of the breaker or fuse ahead of it, from 10 to 6,000 A. Parallel sets, motor circuits and taps have their own rules. A licensed electrician installs the circuit.

Overcurrent device rating, A

The breaker or fuse ahead of the circuit: not the load and not the wire. For an adjustable-trip breaker, use the setting. A rating between two rows of the table takes the next row up.

Ground wire material

Table 250.122 has one column for copper and one for aluminum or copper-clad aluminum.

Circuit conductor material

The ground wire is held to the circuit wire size (250.122(A)) only when both are the same metal. It does not change the increase.

Smallest circuit conductor size that carries the load

For the increase of 250.122(B). The size you would use with no voltage drop upsizing, after any temperature or conductor-count correction. Leave as not entered if the circuit wire was not made larger.

Circuit conductor size installed

The size you are pulling, for example after upsizing for voltage drop. With it entered, a ground wire of the same metal is also held to this size (250.122(A)).

Example result for the default inputs

200 A overcurrent device, copper ground wire, 250 kcmil copper circuit conductors. NEC 250.122.

Table 250.122 minimum

6 AWG

Increase ratio

1.4899 x

Ground wire to install

4 AWG

Calculation details
Overcurrent device	200 A is a standard rating (Table 240.6(A)). It is a row of Table 250.122.
Table 250.122, 200 A row	6 AWG copper, 4 AWG aluminum or copper-clad aluminum. For copper: 6 AWG, 26,240 cmil.
Circuit conductors increased, 250.122(B)	250 kcmil / 3/0 AWG = 250,000 cmil / 167,800 cmil = 1.4899
Ground wire increased	26,240 cmil x 1.4899 = 39,094 cmil. The next size up in Chapter 9 Table 8 is 4 AWG, 41,740 cmil.
Ground wire	4 AWG copper, 41,740 cmil, as a minimum. A longer run or a high fault current can call for a larger wire (the note under Table 250.122, with 250.4(A)(5) and (B)(4)).

For estimation purposes only. Consult a licensed engineer for final designs.

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How the ground wire size is worked

The equipment grounding conductor (EGC) carries ground-fault current back to the source so the breaker opens. NEC Table 250.122 sizes it from the rating of the breaker or fuse ahead of the circuit, not from the load. If the circuit wires were made larger for a reason other than temperature or conductor-count corrections, usually voltage drop, a wire-type ground wire grows in the same proportion of circular mil area. The ground wire never has to be larger than the circuit wires.

Table minimum: first row of Table 250.122 with a rating at or above the device ratingThe table reads "not exceeding", so a rating between two rows takes the next row up. A 225 A breaker is not on the table; it takes the 300 A row, 4 AWG copper or 2 AWG aluminum. A 60 A breaker takes 10 AWG copper or 8 AWG aluminum, and so do 30, 40 and 50 A.
Ratio of increase: ratio = installed circuit wire area / smallest size that carries the loadAreas are in circular mils from Chapter 9 Table 8, and a kcmil size is the number x 1,000. 3/0 AWG replaced by 250 kcmil is 250,000 cmil / 167,800 cmil = 1.4899.
Increased ground wire: table size area x ratio, then the next standard size upFor the 200 A feeder, 6 AWG is 26,240 cmil, x 1.4899 = 39,094 cmil. No standard size has exactly that area, and the next one up in Table 8 is 4 AWG, 41,740 cmil.
Limit: ground wire no larger than the circuit wires, 250.122(A)The ground wire is not required to be larger than the circuit conductors. A 30 A breaker takes 10 AWG from the table, but on 14 AWG circuit wire the ground wire is 14 AWG, the answer Mike Holt gives for a 14 AWG motor circuit.
When the increase applies: circuit wire increased for any reason other than 310.15(B) or 310.15(C)The 2020 text of 250.122(B). Making the circuit wire larger for voltage drop, short-circuit rating or future capacity counts. Making it larger only to carry the load after a temperature correction or an adjustment for more than three current-carrying conductors does not. Enter the size after those corrections as the smallest size that carries the load.

Eight circuits through the same formula

The first three rows are the worked examples of IAEI Magazine, Mike Holt and EEPower, and the page gives the same sizes. The next four read the table with the circuit wire unchanged, and the last one is Mike Holt's motor circuit, where the ground wire is held to the size of the circuit wire.

Table 250.122 row, table sizes and the ground wire to install for eight circuits
Circuit	Table row, A	Table copper	Table aluminum	Copper ground wire to install
200 A feeder, 3/0 AWG to 250 kcmil copper (IAEI)	200	6 AWG	4 AWG	4 AWG
40 A circuit, 8 AWG to 6 AWG copper (Mike Holt)	60	10 AWG	8 AWG	8 AWG
250 A device, 250 to 350 kcmil copper (EEPower)	300	4 AWG	2 AWG	2 AWG
60 A circuit, wire not increased	60	10 AWG	8 AWG	10 AWG
100 A circuit, wire not increased	100	8 AWG	6 AWG	8 AWG
200 A feeder, wire not increased	200	6 AWG	4 AWG	6 AWG
400 A feeder, wire not increased	400	3 AWG	1 AWG	3 AWG
30 A breaker on 14 AWG circuit wire (Mike Holt)	60	10 AWG	8 AWG	14 AWG

On the 200 A feeder the circuit wire grows by 1.4899 and the 6 AWG ground wire becomes 4 AWG. On a 20 A circuit, 12 AWG circuit wire moved to 10 AWG takes the ground wire from 12 AWG to 10 AWG. Aluminum ground wire is one or more sizes larger on every row.

Standards and data sources

NEC 2023, 250.122, Table 250.122, Table 240.6(A) and Chapter 9 Table 8 - the table of minimum equipment grounding conductors by overcurrent device rating, the increase for larger circuit conductors, the limit that the ground wire need not exceed the circuit conductors, the standard device ratings and the circular mil areas. The NEC text was read as others print it, not in NFPA's viewer.
L. Keith Lofland in IAEI Magazine, Sizing of Conductors Related to Grounding & Bonding (2021) - the 2020 wording of 250.122(B), the 225 A breaker that takes the 300 A row, the note under Table 250.122, and the 200 A feeder with 250 kcmil copper in place of 3/0 AWG that this page opens on.
Mike Holt Enterprises, Understanding 2020 NEC Requirements for Bonding and Grounding, 250.122 - the copper column of Table 250.122, the 40 A circuit with phase conductors moved from 8 AWG to 6 AWG for voltage drop (10 AWG ground wire becomes 8 AWG), and the 14 AWG motor circuit on a 30 A breaker.
Lorenzo Mari in EEPower, NEC 2023 Basics: Sizing Equipment Grounding Conductors (2023) - the 250 A breaker that takes the 300 A row, the 60 A, 400 A and 2,000 A rows, the 350 kcmil circuit that takes 4 AWG up to 2 AWG, and the statement that temperature and conductor-count corrections do not trigger the increase.
Electrical License Renewal and JADE Learning on the 2020 changes to 250.122 - the 2011, 2014 and 2020 wording of 250.122(B), and the 2020 change that raised the aluminum size on the 5,000 A and 6,000 A rows from 1200 to 1250 kcmil.

Limitations of this calculator

This page gives preliminary numbers for estimating and for checking a quote or a plan. A licensed electrician sizes and installs the circuit under the permit and the inspection of the local authority having jurisdiction (AHJ). Nothing here is an approval of an installation.
Table 250.122 gives the minimum. The note under it says the ground wire might need to be larger to meet 250.4(A)(5) or 250.4(B)(4), for a long run or a high fault current. The 2020 text lets a qualified person size the ground wire by calculation for an effective ground-fault path instead of using the proportional increase. This page does neither.
The NEC text was read as IAEI Magazine, Mike Holt, EEPower, Electrical License Renewal and JADE Learning print it, not in NFPA's own viewer. The wording of 250.122(B) quoted here is the 2020 text. The 2023 text itself was not read; EEPower's 2023 article gives the same rule and the same exclusions. Check the edition your AHJ adopted.
The table values are the 2020 and later ones. In the 2017 edition the aluminum size on the 5,000 A and 6,000 A rows was 1200 kcmil, and 250.122(B) was worded differently. Several chart sites still print the old 1200 kcmil.
Only the wire-type ground wire is sized. A metal raceway, cable armor and the other paths listed in 250.118 can serve as the ground path and are not sized here. Aluminum and copper-clad aluminum ground wire has installation limits of its own in 250.120(B).
Parallel circuit conductors (250.122(F)), several circuits in one raceway (250.122(C)), motor circuits (250.122(D)), flexible cord (250.122(E)) and feeder taps (250.122(G)) have their own rules. In several circuits in one raceway a single ground wire is sized for the largest device; enter that device's rating. Parallel sets in separate raceways take a full-size ground wire in each. The page does not check these arrangements.
The page takes the two circuit conductor sizes as you enter them and does not check ampacity, terminal ratings or that the breaker protects the wire. Use the AC wire size calculator for the wire and the voltage drop calculator for the run.
The device rating runs from 10 to 6,000 A, the extent of Table 250.122. The page does not size the grounding electrode conductor (Table 250.66), the main bonding jumper or other bonding jumpers.

Common mistakes with ground wire size

Sizing the ground wire from the circuit wire. Table 250.122 is entered with the breaker rating. A 50 A breaker on 6 AWG circuit wire, where 6 AWG is the smallest size that carries the load, takes the 60 A row, 10 AWG copper, the row that also covers 30 A and 40 A breakers. A ground wire as large as the circuit wire is allowed but not required. When the circuit wire was increased, 250.122(B) raises the ground wire in proportion to the area, which on this page takes the 200 A feeder from 6 AWG to 4 AWG, not to the 250 kcmil of the circuit.
Reading the nearest row instead of the next one up. A 225 A breaker sits between the 200 A and 300 A rows. The table says "not exceeding", so it takes the 300 A row, 4 AWG copper, not the 6 AWG of the 200 A row. An 80 A breaker takes the 100 A row, 8 AWG copper.
Leaving the ground wire alone after a voltage drop upsize. A 20 A circuit on 12 AWG copper moved to 10 AWG for voltage drop has a 12 AWG ground wire in the table. The circuit wire grew by 1.5896, so the ground wire grows the same way: 6,530 cmil x 1.5896 = 10,380 cmil, which is 10 AWG. A 12 AWG ground wire with 10 AWG circuit wire fails 250.122(B).
Rounding the increased ground wire down. The 200 A feeder example works out to 39,094 cmil. 6 AWG is 26,240 cmil, too small, and the next size is 4 AWG at 41,740 cmil. The result is the next standard size at or above the area, never below it. The 40 A example from Mike Holt lands just under a size, 16,497 cmil against 16,510 cmil for 8 AWG, and 8 AWG covers it.
Treating a derating increase as a trigger. If the circuit wire was made larger only to carry the load after a temperature correction or an adjustment for more than three current-carrying conductors (310.15(B) and 310.15(C)), the 2020 text of 250.122(B) does not call for a larger ground wire. Enter the size that the corrected load needs as the smallest size, and the page shows no increase. Making it larger for voltage drop on top of that does count.
Using the wrong column. The table has a copper column and an aluminum or copper-clad aluminum column, and aluminum is larger. A 100 A breaker takes 8 AWG copper but 6 AWG aluminum; a 400 A feeder takes 3 AWG copper and 1 AWG aluminum. Pick the material of the ground wire, not of the circuit wire.

Common questions about ground wire size

What size ground wire for a 60 amp breaker?

10 AWG copper or 8 AWG aluminum or copper-clad aluminum, from the 60 A row of Table 250.122. The same row covers breakers above 20 A up to 60 A, so a 30, 40 or 50 A breaker takes it too. The table is entered with the breaker rating, not the load or the size of the circuit wire.

What size ground wire for a 100 amp breaker?

8 AWG copper or 6 AWG aluminum or copper-clad aluminum, from the 100 A row. Breakers above 60 A up to 100 A use it. An 80 A breaker is not on the table, so it takes the 100 A row: 8 AWG copper or 6 AWG aluminum. This is the minimum; a long run or an upsized circuit wire can call for more.

What size ground wire for a 200 amp breaker?

6 AWG copper or 4 AWG aluminum or copper-clad aluminum, from the 200 A row. That covers breakers above 100 A up to 200 A. A 225 A or 250 A breaker takes the 300 A row, 4 AWG copper or 2 AWG aluminum. If the feeder wire was made larger for voltage drop, the ground wire grows too.

Do I upsize the ground wire when I upsize the wire for voltage drop?

Yes. 250.122(B) says that if the ungrounded conductors are increased in size for any reason other than 310.15(B) or 310.15(C), a wire-type ground wire is increased in proportion to circular mil area. On a 20 A circuit, 12 AWG circuit wire moved to 10 AWG is a ratio of 1.5896, and the 12 AWG ground wire becomes 10 AWG. On a 200 A feeder, 3/0 AWG moved to 250 kcmil is 1.4899, and the 6 AWG ground wire becomes 4 AWG copper, or 2 AWG in aluminum.

What is the ground wire for a 100 amp feeder run in larger wire for distance?

A 100 A feeder on 3 AWG copper moved up to 1/0 AWG is 105,600 cmil / 52,620 cmil = 2.0068. The table ground wire is 8 AWG, 16,510 cmil, and x 2.0068 is 33,133 cmil, so the ground wire is 4 AWG copper. The voltage drop calculator tells you whether the circuit wire needs to go up in the first place.

Does the ground wire go up when the circuit wire is derated for heat or for more than three conductors?

Not under the 2020 text. 250.122(B) excludes an increase required by 310.15(B), the temperature correction, and by 310.15(C), the adjustment for more than three current-carrying conductors. EEPower's 2023 article gives the same exclusions. An increase for voltage drop does count. Check the edition your AHJ adopted.

Can the ground wire be larger than the circuit wires?

It does not have to be. 250.122(A) says the ground wire is not required to be larger than the circuit conductors. A 30 A breaker takes 10 AWG from the table, but a 14 AWG motor circuit on it needs only 14 AWG, the answer in Mike Holt's textbook.

What if several circuits share one conduit?

One ground wire can serve them all, sized for the largest breaker. IAEI's example is 20, 30, 50 and 60 A circuits in one raceway, which take one ground wire for the 60 A breaker: 10 AWG copper. Enter the largest rating in the calculator.

How is this different from the grounding electrode conductor?

The equipment grounding conductor runs with the circuit conductors and carries fault current back so the breaker opens; it is sized from the breaker rating in Table 250.122. The grounding electrode conductor connects the service to the ground rod or other electrode and is sized from the service conductors in Table 250.66. They are different wires with different tables.

Does this replace an electrician?

No. This page is for estimating and for checking numbers on a quote or a plan. A licensed electrician sizes and installs the circuit under a permit, and the local authority having jurisdiction inspects it.