Ground Wire Size Chart: NEC Grounding Conductor Size Chart

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.

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)

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. 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)

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.