Ground Wire Size Calculator (NEC 250.122 Standard)

Table of Contents

Ground wire size calculator based on NEC 250.122 Standard

Does this calculator work for service entrance? Of course not. This is for equipment grounding (EGC) based on breaker size (Table NEC 250.122), not for service grounding (Table 250.66).

⏚ Grounding Size Calculator

Based on NEC Table 250.122 (Safety Standards)

1. Overcurrent Device Rating (Breaker/Fuse): *Enter the Ampere rating of the Circuit Breaker protecting the equipment.

2. Conductor Material:

Minimum Grounding Wire Size: … …

Compliance Note:
Based on NEC 250.122 for Copper.
*Metric (mm²) values are approximate conversions for reference.

What is grounding in electrical?

Grounding or earthing in the engineering is the connection of an electrical system to the soil (earth).

It creates a direct and low resistance path for excess electricity to dissipate safely into the ground, rather than passing through a person or sensitive equipment. This can prevent the electric shock to harm people and damaging equipment. All building needs to have a grounding system, if not, it will be very dangerous for people who lived or stay or unlucky inside the building.

What is ground wire size chart?

Ground wire size refers to the physical thickness of the minimum cable size for safety that connect electrical equipment to the earth (ground). This ground wire usually have the color yellow & green.

Ground wire size table base on NEC

There is no formula in determining the ground wire size. We should look at the NEC table and NEC chart as the base on determining the ground wire size.

NEC Table 250.122 Cheat Sheet

Minimum Size of Equipment Grounding Conductors

Breaker Rating (Overcurrent Device)	Copper Wire (Most Common)	Aluminum Wire (Aluminum/CCA)
15 Amps	14 AWG	12 AWG
20 Amps	12 AWG	10 AWG
30 - 60 Amps	10 AWG	8 AWG
100 Amps	8 AWG	6 AWG
200 Amps	6 AWG	4 AWG
300 Amps	4 AWG	2 AWG
400 Amps	3 AWG	1 AWG
500 Amps	2 AWG	1/0 AWG
600 Amps	1 AWG	2/0 AWG
800 Amps	1/0 AWG	3/0 AWG
1000 Amps	2/0 AWG	4/0 AWG
1200 Amps	3/0 AWG	250 kcmil
1600 Amps	4/0 AWG	350 kcmil
2000 Amps	250 kcmil	400 kcmil

Note: Data is based on NFPA 70 National Electrical Code (NEC). If the breaker size falls between standard ratings (e.g., 70A), use the wire size for the next higher rating (e.g., use the 100A row).

AWG to Metric Conversion Table (mm2)

Wire Size Conversion: AWG to Metric (mm²)

Cross-Reference for NEC Standards to International Metric Sizes

AWG Size (NEC Standard)	Actual Area (mm² Equivalent)	Recommended Metric (Standard mm²)
14 AWG	2.08 mm²	2.5 mm²
12 AWG	3.31 mm²	4 mm²
10 AWG	5.26 mm²	6 mm²
8 AWG	8.37 mm²	10 mm²
6 AWG	13.3 mm²	16 mm²
4 AWG	21.2 mm²	25 mm²
2 AWG	33.6 mm²	35 mm²
1 AWG	42.4 mm²	50 mm²
1/0 AWG	53.5 mm²	70 mm²
2/0 AWG	67.4 mm²	70 mm²
3/0 AWG	85.0 mm²	95 mm²
4/0 AWG	107 mm²	120 mm²

Technical Note: Since AWG and Metric sizes do not match exactly, this table recommends the next larger metric size (Upsizing). This ensures the conductor maintains a lower resistance than the minimum required by NEC/NFPA standards.

Understanding NEC 250.122

We talked much about NEC. What is it? In the world of electrical engineering, determining the size of the equipment grounding conductor (EGC) correctly is a MUST. It is very critical for safety.

The contractors / installers / applicators must ensure that if a fault occurs, the breaker must immediately trip, otherwise it will be very dangerous and causes electric shock.

Now, engpocket friends already know how to determine the ground wire size, we are wonder, do you eager to use our watts to amps calculator and converting 3 phase and single phase on this link? Check it out