NEC Ground Wire Size Chart: What Size Ground Wire Do You Need + Amps?

For every wire, you will need a ground wire. As you may know, the ground wire doesn’t have to be as big as the main wire. Example: 1 AWG copper wire doesn’t require a 1 AWG copper ground wire. It requires a 6 AWG copper ground wire. A ground wire size chart that follows will tell you exactly the size of the grounding conductor you need.

Now, it’s important to understand that you cannot go wrong with a bigger-than-required ground wire. A big ground wire is just overkill that will cost you more. That’s it.

what size ground wire do i need
With smaller wires (8 AWG or smaller), you can use the same size ground wire as the main (hot) wire.

To find the most optimum ground wire size, you have to consult the ‘NEC Grounding Conduction Size Chart’.

What section of the NEC covers grounding?

National Electrical Code (NEC) covers the sizes of ground wires in Article 250, Table 250.66 titled ‘Grounding Electrode Conductor For Alternativing Current Systems’. This 250.66 NEC table is also known as the equipment grounding conductor size chart.

Since it’s not all that easy to get hands on these new 2020 NEC guidelines, we are sharing this chart below. You will see two charts:

  • 1st chart covers the size of copper wires (from 8 AWG to 2000 kcmil) and their corresponding copper ground wires.
  • 2nd chart covers the size of aluminum wires (from 6 AWG to 2000 kcmil) and their corresponding aluminum ground wires.

To figure out what size ground wire you need, just consult these two charts. Below each chart, we also list some examples of ground wire sizing choices:

Copper Ground Wire Size Chart (Copper Grounding Conductor Size Chart)

Size Of Copper Wire (AWG or kcmil): Copper Grounding Electrode Conductor Size (AWG or kcmil): Amps:
8 AWG Copper Wire 8 AWG Copper Ground Wire 50 Amps
6 AWG Copper Wire 8 AWG Copper Ground Wire 65 Amps
4 AWG Copper Wire 8 AWG Copper Ground Wire 85 Amps
3 AWG Copper Wire 8 AWG Copper Ground Wire 100 Amps
2 AWG Copper Wire 8 AWG Copper Ground Wire 115 Amps
1 AWG Copper Wire 6 AWG Copper Ground Wire 130 Amps
0 (1/0) AWG Copper Wire 6 AWG Copper Ground Wire 150 Amps
00 (2/0) AWG Copper Wire 4 AWG Copper Ground Wire 175 Amps
000 (3/0) AWG Copper Wire 4 AWG Copper Ground Wire 200 Amps
0000 (4/0) AWG Copper Wire 2 AWG Copper Ground Wire 230 Amps
250 kcmil Copper Wire 2 AWG Copper Ground Wire 255 Amps
300 kcmil Copper Wire 2 AWG Copper Ground Wire 285 Amps
350 kcmil Copper Wire 2 AWG Copper Ground Wire 310 Amps
400 kcmil Copper Wire 0 (1/0) AWG Copper Ground Wire 335 Amps
500 kcmil Copper Wire 0 (1/0) AWG Copper Ground Wire 380 Amps
600 kcmil Copper Wire 0 (1/0) AWG Copper Ground Wire 420 Amps
700 kcmil Copper Wire 00 (2/0) AWG Copper Ground Wire 460 Amps
750 kcmil Copper Wire 00 (2/0) AWG Copper Ground Wire 475 Amps
800 kcmil Copper Wire 00 (2/0) AWG Copper Ground Wire 490 Amps
900 kcmil Copper Wire 00 (2/0) AWG Copper Ground Wire 520 Amps
1000 kcmil Copper Wire 00 (2/0) AWG Copper Ground Wire 545 Amps
1250 kcmil Copper Wire 000 (3/0) AWG Copper Ground Wire 590 Amps
1500 kcmil Copper Wire 000 (3/0) AWG Copper Ground Wire 625 Amps
1750 kcmil Copper Wire 000 (3/0) AWG Copper Ground Wire 650 Amps
2000 kcmil Copper Wire 000 (3/0) AWG Copper Ground Wire 665 Amps

Let’s look at two examples:

What size ground wire do I need for a 3 AWG wire?

3 AWG wire has an ampacity of 100A at a median 75°C (167°C) temperature. This is also why people confuse it with being a 100 amp wire. You can check what size wire you need for 100 amps here.

To figure out the size of the ground wire, you consult the copper grounding conductor size chart, and you see that you need an 8 AWG copper ground wire for 3 AWG copper wire (for 100 amps, you can use 8 AWG copper ground wire). Now, there is nothing wrong if you use a 6 AWG or even 4 AWG ground wire; it will do the same job, it will just cost more.

What size ground wire do I need for 250 kcmil wire?

250 kcmil copper wire has a 255A ampacity at a median conductor temperature. If you apply the NEC 80% rule, 250 kcmil wire can handle up to 204 amps. That’s why it is considered a 200 amp wire. Basically, we are trying to answer what ground wire do you need for 200 amp service.

If you consult the copper ground wire size chart above, you can see that you will need a 2 AWG copper ground wire to adequately ground a 250 kcmil wire. Basically, you need a 2 AWG copper ground wire for a 200 amp service.

Let’s look at the NEC recommendations for aluminum wires as well:

Aluminum Ground Wire Size Chart (Aluminum Grounding Conductor Size Chart)

Size Of Aluminum Wire (AWG or kcmil): Aluminum Grounding Electrode Conductor Size (AWG or kcmil): Amps:
6 AWG Aluminum Wire 6 AWG Aluminum Ground Wire 60 Amps
4 AWG Aluminum Wire 6 AWG Aluminum Ground Wire 75 Amps
3 AWG Aluminum Wire 6 AWG Aluminum Ground Wire 85 Amps
2 AWG Aluminum Wire 6 AWG Aluminum Ground Wire 100 Amps
1 AWG Aluminum Wire 4 AWG Aluminum Ground Wire 115 Amps
0 (1/0) AWG Aluminum Wire 4 AWG Aluminum Ground Wire 135 Amps
00 (2/0) AWG Aluminum Wire 2 AWG Aluminum Ground Wire 150 Amps
000 (3/0) AWG Aluminum Wire 2 AWG Aluminum Ground Wire 175 Amps
0000 (4/0) AWG Aluminum Wire 0 (1/0) AWG Aluminum Ground Wire 205 Amps
250 kcmil Aluminum Wire 0 (1/0) AWG Aluminum Ground Wire 230 Amps
300 kcmil Aluminum Wire 0 (1/0) AWG Aluminum Ground Wire 255 Amps
350 kcmil Aluminum Wire 0 (1/0) AWG Aluminum Ground Wire 280 Amps
400 kcmil Aluminum Wire 000 (3/0) AWG Aluminum Ground Wire 305 Amps
500 kcmil Aluminum Wire 000 (3/0) AWG Aluminum Ground Wire 350 Amps
600 kcmil Aluminum Wire 000 (3/0) AWG Aluminum Ground Wire 385 Amps
700 kcmil Aluminum Wire 0000 (4/0) AWG Aluminum Ground Wire 420 Amps
750 kcmil Aluminum Wire 0000 (4/0) AWG Aluminum Ground Wire 435 Amps
800 kcmil Aluminum Wire 0000 (4/0) AWG Aluminum Ground Wire 450 Amps
900 kcmil Aluminum Wire 0000 (4/0) AWG Aluminum Ground Wire 480 Amps
1000 kcmil Aluminum Wire 0000 (4/0) AWG Aluminum Ground Wire 500 Amps
1250 kcmil Aluminum Wire 250 kcmil Aluminum Ground Wire 545 Amps
1500 kcmil Aluminum Wire 250 kcmil Aluminum Ground Wire 585 Amps
1750 kcmil Aluminum Wire 250 kcmil Aluminum Ground Wire 615 Amps
2000 kcmil Aluminum Wire 250 kcmil Aluminum Ground Wire 630 Amps

Compared to copper wires, aluminum wires have about 39% lower conductivity. That’s why you have to use different grounding wires for aluminum wires.

Let’s look at two examples of aluminum ground wires:

How big aluminum ground wire do you need for a 00 AWG aluminum wire?

Just check the aluminum ground wire size table above and you will see that you need a 2 AWG aluminum ground wire for 00 AWG aluminum wire grounding.

What size ground wire do I need for 500 kcmil aluminum wire?

Same thing. Check the NEC equipment grounding conductor chart for aluminum wires above, and you will see that you need a 000 AWG aluminum ground wire for adequately grounding a 500 kcmil aluminum wire.

With these two charts, you can pretty much figure out how big equipment grounding conductors you need. If you have any questions, just use the comments below and we’ll try to help you out.

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