There are two distinct types of ground wire size charts as governed by the National Electric Code. The first one is the Equipment Grounding Conductor (EGC) chart, based on NEC 250.122. This chart is used to size the ground wire that runs with branch circuits and feeders.

The second is the Grounding Electrode Conductor (GEC) chart, defined in NEC 250.66, which is used to size the wire that connects the electrical service or separately derived system to grounding electrodes, such as rods, rebar, or building steel. While both are technically "ground wires," they serve very different roles: one ensures breaker protection (EGC), and the other ensures earth bonding (GEC). You should use the EGC chart when sizing the ground wire for branch circuits or feeders, and the GEC chart when sizing the wire that connects the main service or transformer to a grounding electrode. Here are both NEC ground wire size charts for your reference:

Equipment Grounding Conductor (EGC) Ground Wire Size Chart

• EGC, or Equipment Grounding Conductor, is the green or bare copper wire that runs with your hot and neutral conductors, which carries fault current back to the breaker. The EGC size chart is based on breaker size, not load, because the ground wire must be thick enough to withstand a short-circuit surge without melting.

• If you increase the hot conductor size to reduce voltage drop, the EGC must be increased in the same proportion. For example, let's say a 100 A feeder normally uses 3 AWG copper with an 8 AWG EGC. If you upsize the feeder to 1 AWG for voltage drop, the EGC must also be upsized proportionally to 6 AWG.

• Metal raceways (EMT, IMC, RMC, rigid aluminium) may serve as the equipment grounding conductor if properly installed and bonded. However, PVC is never allowed to be used as an equipment grounding conductor. If conduit is used as EGC, the ECG table does not apply, as the raceway itself serves as the grounding conductor and performs the grounding function.

• Cables like NM-B, UF-B, MC, AC, and SER often contain grounding wires smaller than those permitted by Table 250.122, provided they are listed as an assembly.

• Aluminium or copper-clad aluminium EGCs can be used, but their applications are limited. They are never smaller than 8 AWG and cannot be used when exposed to corrosion. Copper is used almost everywhere at currents below 100 A.

• When you run phase conductors in parallel (e.g., two 1 AWG wires per phase in two raceways), you must also run an EGC in each raceway.

Grounding Electrode Conductor (GEC) Ground Wire Size Chart

• The GEC, or Grounding Electrode Conductor, is the wire that connects the grounded neutral in your electrical service panel to earth via ground rod, concrete-encased rebar (Ufer), or building steel. It stabilises voltage during lightning strikes and utility surges by bonding your electrical system to the earth.

• The GEC size is based on the largest ungrounded service conductor, not the breaker. For example, if you’re using 3/0 copper conductors for a 200 A service, you must size your GEC to that conductor, which means 2 AWG copper to a building steel electrode. But if you’re only connecting to ground rods, the NEC limits the required GEC size to 6 AWG copper, no matter how large the service is.

• Some grounding electrodes have fixed minimum or maximum requirements:

• For ground rods, pipe, or plate electrodes, you are never required to go larger than 6 AWG copper or 4 AWG aluminium.

• For concrete-encased electrodes (Ufer) and building steel, there is no upper limit; refer to the full 250.66 table.

• For ground rings, the GEC must be at least 2 AWG copper, even if the table suggests a smaller size.

• If you have parallel service conductors, their sizes must be combined to determine the appropriate GEC size. For instance, two parallel 2/0 copper conductors equal 4/0, so GEC must be sized accordingly.

• Rebar may qualify as a grounding electrode if it meets NEC 250.52(A)(3) (minimum 20 ft, ½″ diameter, in direct contact with concrete). If used, the GEC must run from the service to the rebar and follow the full sizing table unless it is a ground rod

• Aluminum GECs are permitted, but must be:

• At least 8 AWG

• Not installed in corrosive or damp locations

• Terminated using lugs rated for aluminum

At Nassau National Cable, you can buy NM-B, UF-B, SER, MC, and AC cables that come with a pre-installed equipment grounding conductor (EGC), as well as bare copper grounding wire for grounding electrode conductor (GEC) applications.

FAQ

What size ground wire do I need for 400 amps?

For a 400A breaker, you typically need a 3 AWG copper EGC or a 1 AWG copper GEC, depending on the application.

What size ground wire for 50 amps?

You’ll need a 10 AWG copper ground wire for a 50A circuit if it’s acting as an EGC. If used as a GEC, size depends on the service conductors.

Why aren’t ground wires insulated?

Ground wires are bare because insulation isn’t required in most dry locations.

Do ground wires need to be insulated?

Only in wet or corrosive environments.

Can aluminum be used as a ground wire?

Yes, aluminum ground wire is allowed by NEC as long as it is at least 8 AWG, protected from corrosion, and not installed in damp areas.

Is aluminum a good ground?

It’s effective when sized and installed properly, though copper is preferred for smaller circuits. You need to use terminals rated for aluminum and antioxidant paste.

Can rebar be used as a grounding rod?

Yes, if it meets NEC requirements for a concrete-encased electrode (≥20 ft long, ½″ diameter, in contact with concrete).

What can be used as a grounding rod?

Accepted options include copper or galvanized rods, steel pipe, rebar (Ufer), building steel, and ground rings.