Ground Wire Size Chart (NEC 250.122 & 250.66)
Ground wire sizes for every circuit and service: equipment grounding conductors by breaker rating per NEC Table 250.122, and grounding electrode conductors by service size per NEC Table 250.66, in both copper and aluminum.
Two Different Ground Wires, Two Different Tables
“What size ground wire?” has two answers, because the NEC defines two different grounding conductors sized from two different tables. Using the wrong table is one of the most common grounding mistakes.
The equipment grounding conductor (EGC) is the ground wire that runs with the circuit conductors to receptacles, appliances, and equipment enclosures. Its job is to carry fault current back to the source so the breaker trips quickly. It is sized from Table 250.122based on the rating of the breaker or fuse protecting the circuit — not on the size of the hot wires.
The grounding electrode conductor (GEC) connects the service neutral (and enclosure) to the grounding electrode system — ground rods, a concrete-encased (Ufer) electrode, or a metal water pipe. Its job is to dissipate lightning and surges to earth. It is sized from Table 250.66 based on the size of the largest ungrounded service-entrance conductor.
Quick rule:Ground wire inside a circuit or feeder → Table 250.122 (by breaker size). Ground wire from the service panel to ground rods or a Ufer → Table 250.66 (by service conductor size).
Equipment Grounding Conductor Sizes — NEC Table 250.122
Minimum EGC size based on the rating of the overcurrent device (breaker or fuse) ahead of the circuit
| Breaker / Fuse Rating | Copper EGC | Aluminum EGC |
|---|---|---|
| 15A | #14 | #12 |
| 20A | #12 | #10 |
| 60A | #10 | #8 |
| 100A | #8 | #6 |
| 200A | #6 | #4 |
| 300A | #4 | #2 |
| 400A | #3 | #1 |
| 500A | #2 | 1/0 |
| 600A | #1 | 2/0 |
| 800A | 1/0 | 3/0 |
How to read it: Use the row matching (or the next row above) your breaker rating. A 30, 40, or 50-amp breaker falls under the 60A row: #10 copper. Per NEC 250.122(A), the EGC is never required to be larger than the circuit conductors. Aluminum column also applies to copper-clad aluminum.
Grounding Electrode Conductor Sizes — NEC Table 250.66
Minimum GEC size based on the largest ungrounded service-entrance conductor (copper sizes shown)
| Largest Copper Service-Entrance Conductor | Copper GEC | Aluminum GEC |
|---|---|---|
| #2 or smaller | #8 | #6 |
| #1 or 1/0 | #6 | #4 |
| 2/0 or 3/0 | #4 | #2 |
| Over 3/0 through 350 kcmil | #2 | 1/0 |
| Over 350 through 600 kcmil | 1/0 | 3/0 |
250.66(A) — Rod, pipe, and plate electrodes: Where the GEC runs only to ground rods, pipe, or plate electrodes, it is never required to be larger than #6 copper (or #4 aluminum), regardless of service size.
250.66(B) — Concrete-encased (Ufer) electrodes: Where the GEC runs only to a concrete-encased electrode, it is never required to be larger than #4 copper.
When to Upsize the Ground Wire
If you upsize the circuit conductors, you must upsize the equipment grounding conductor too. Per NEC 250.122(B), when ungrounded (hot) conductors are increased in size — most commonly to compensate for voltage dropon a long run — the EGC must be increased proportionally, based on the ratio of the circular-mil areas of the new and original conductors.
Example:A 20-amp circuit normally uses #12 copper hots (6,530 circular mils) with a #12 copper EGC. If the run is long and you upsize the hots to #8 copper (16,510 circular mils), the ratio is 16,510 ÷ 6,530 = 2.53. The EGC must be at least 6,530 × 2.53 = 16,510 circular mils — so the ground wire also becomes #8 copper.
This rule prevents a situation where a long, upsized circuit has a proportionally undersized fault-current path, which would raise ground-fault impedance and slow breaker tripping. The GEC, by contrast, is never upsized for voltage drop — only Table 250.66 and the electrode-type caps of 250.66(A) and (B) apply.
Frequently Asked Questions
What size ground wire for a 200 amp service?
For a 200-amp breaker or feeder, NEC Table 250.122 requires a #6 copper (or #4 aluminum) equipment grounding conductor. For the grounding electrode conductor at a 200-amp service (typically 2/0 or 3/0 copper service-entrance conductors), NEC Table 250.66 requires #4 copper — but if the GEC runs only to ground rods, NEC 250.66(A) says it never needs to be larger than #6 copper, and if it runs only to a concrete-encased electrode (Ufer), #4 copper is sufficient per 250.66(B).
What size ground wire for a 100 amp subpanel?
A 100-amp subpanel feeder requires a #8 copper (or #6 aluminum) equipment grounding conductor per NEC Table 250.122. The EGC runs with the feeder conductors from the main panel to the subpanel. Remember that in a subpanel, neutrals and grounds must be kept separate — the ground bar bonds to the enclosure, while the neutral bar floats.
Can a ground wire be smaller than the hot wire?
Yes. Equipment grounding conductors are sized from Table 250.122 based on the breaker rating, not the circuit conductors, and above 60 amps the EGC is smaller than the hot wires. For example, a 200-amp feeder uses 3/0 copper hots but only a #6 copper EGC. The ground wire only carries current during a fault, and only long enough to trip the breaker, so it doesn't need the same continuous ampacity. It can never be smaller than Table 250.122 requires, and per 250.122(A) it never needs to be larger than the circuit conductors.
What is the difference between an equipment grounding conductor and a grounding electrode conductor?
The equipment grounding conductor (EGC) is the ground wire that runs with circuit conductors to metal parts of equipment — it carries fault current back to the source to trip the breaker, and is sized by breaker rating per Table 250.122. The grounding electrode conductor (GEC) connects the service neutral to the grounding electrode system (ground rods, Ufer, water pipe) — it handles lightning and surge events, and is sized by the service-entrance conductor size per Table 250.66.
What size ground wire for a 60 amp circuit?
A 60-amp circuit requires a #10 copper (or #8 aluminum) equipment grounding conductor per NEC Table 250.122. This applies to 60-amp subpanel feeders, tankless water heaters, and similar circuits. Note that #10 is smaller than the #6 copper hot conductors typically used on a 60-amp circuit — that's normal and code-compliant.
Related Electrical Calculators
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