Ground Wire Size Chart — NEC Table 250.122 Complete Grounding Guide 2026
The equipment grounding conductor (EGC) must be sized per NEC Table 250.122 based on the overcurrent device (breaker) protecting the circuit. Common sizes: 15A circuit = 14 AWG, 20A = 12 AWG, 50A = 10 AWG, 100A = 8 AWG, 200A = 6 AWG. This guide covers both equipment grounding and grounding electrode conductors.
NEC Table 250.122 — Equipment Grounding Conductor
The equipment grounding conductor (EGC) provides a low-impedance path for fault current to trip the breaker quickly. NEC 250.122 sizes the EGC based on the rating of the overcurrent device (breaker or fuse) protecting the circuit, not the wire size of the circuit conductors. Key sizes for copper: 15A → 14 AWG. 20A → 12 AWG. 30A → 10 AWG. 40A → 10 AWG. 50A → 10 AWG. 60A → 10 AWG. 100A → 8 AWG. 200A → 6 AWG. 300A → 4 AWG. 400A → 3 AWG.
Equipment Ground vs Grounding Electrode Conductor
There are two different grounding conductors in an electrical system: Equipment Grounding Conductor (EGC): Sized per Table 250.122. Runs with the circuit conductors. Provides fault return path. This is the green or bare wire in NM-B cable. Grounding Electrode Conductor (GEC): Sized per NEC Table 250.66 based on the size of the service entrance conductors. Connects the system ground to the grounding electrode (ground rod, water pipe, Ufer ground). The GEC is typically larger: 4 AWG for a 200A service with 4/0 copper SEC.
Ground Wire in NM-B Cable
When using NM-B cable (Romex), the equipment ground is the bare copper wire included in the cable. NM-B cables are manufactured with the correct ground wire size for the cable rating: 14/2 NM-B: includes 14 AWG ground (for 15A circuits). 12/2 NM-B: includes 12 AWG ground (for 20A circuits). 10/2 NM-B: includes 10 AWG ground (for 30A circuits). 6/3 NM-B: includes 10 AWG ground (for 50A circuits). You do not need to size the ground separately when using NM-B cable — it is already correct.
Sub-Panel Grounding — The Separation Rule
NEC 250.32(B) requires that in a sub-panel, the neutral and ground must be separated (not bonded). The neutral bar is isolated from the enclosure, and a separate ground bar is installed and bonded to the enclosure. The equipment grounding conductor in the feeder cable connects to this separate ground bar. Additionally, NEC 250.32(A) requires a grounding electrode (ground rod) at the sub-panel location if it is in a separate building. This ensures the sub-panel has its own low-impedance ground reference.
| Breaker Size | Ground Wire (Cu) | Ground Wire (Al) | Common Circuit |
|---|---|---|---|
| 15A | 14 AWG | 12 AWG | General lighting |
| 20A | 12 AWG | 10 AWG | Kitchen, bath, laundry |
| 30A | 10 AWG | 8 AWG | Dryer, small AC |
| 40A | 10 AWG | 8 AWG | Range, EV charger |
| 50A | 10 AWG | 8 AWG | Range, sub-panel |
| 60A | 10 AWG | 8 AWG | EV charger, sub-panel |
| 100A | 8 AWG | 6 AWG | Sub-panel feeder |
| 200A | 6 AWG | 4 AWG | Main service |
| 400A | 3 AWG | 1 AWG | Large service |
Ground Rod Requirements
NEC 250.52 and 250.53 require grounding electrodes for the electrical system. The most common type is two 8-foot ground rods (copper-clad steel, 5/8" diameter) driven at least 6 feet apart, connected with 6 AWG copper wire for a 200A service. A single ground rod must have a resistance of 25 ohms or less (NEC 250.53(A)(2)). If resistance exceeds 25 ohms, a supplemental electrode is required — this is why most installations use two rods by default. The Ufer ground (concrete-encased electrode per NEC 250.52(A)(3)) is the most effective grounding method for new construction.
Disclaimer: For educational reference only. Consult a licensed professional.