Ground Wire Size Calculator
Enter the circuit breaker or overcurrent protection rating to estimate a common copper grounding conductor size in AWG or kcmil.
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Recommended Ground Wire
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Enter the breaker or fuse rating and select the conductor material to calculate a recommended grounding conductor size.
What Is a Ground Wire Size Calculator?
A ground wire size calculator helps estimate the equipment grounding conductor size associated with an electrical circuit. Instead of sizing the conductor from normal load current alone, the grounding conductor is commonly related to the rating of the circuit's overcurrent protection device.
Enter the circuit breaker or fuse rating and choose the conductor material. The calculator then selects a corresponding AWG or kcmil grounding conductor size from its reference table.
How to Use the Ground Wire Size Calculator
Enter Breaker Size
Enter the ampere rating of the circuit breaker or fuse protecting the circuit.
Select Material
Choose copper or aluminum / copper-clad aluminum for the grounding conductor.
Get Wire Size
The calculator displays the corresponding grounding conductor size from the reference table.
Ground Wire Size Calculation
Ground wire sizing is different from simply calculating the load conductor size. For an equipment grounding conductor, the size is typically selected according to the rating of the circuit's overcurrent protective device.
Ground Wire Size = Size corresponding to breaker or fuse rating
For example, when a circuit has a 100 amp overcurrent device, the calculator checks the 100 amp row and returns the associated grounding conductor size for the selected conductor material.
Common Ground Wire Size Reference
The following values are included in this calculator as a practical grounding conductor reference. Local electrical regulations and project conditions should always be checked before installation.
| Breaker / Fuse Rating | Copper Ground Wire | Aluminum Ground Wire |
|---|---|---|
| 15 A | 14 AWG | 12 AWG |
| 20 A | 12 AWG | 10 AWG |
| 30 A | 10 AWG | 8 AWG |
| 40–60 A | 10 AWG | 8 AWG |
| 100 A | 8 AWG | 6 AWG |
| 200 A | 6 AWG | 4 AWG |
| 300 A | 4 AWG | 2 AWG |
| 400 A | 3 AWG | 1 AWG |
| 600 A | 1 AWG | 2/0 AWG |
| 800 A | 1/0 AWG | 3/0 AWG |
Why Proper Ground Wire Sizing Matters
The grounding conductor provides a low-impedance path for fault current so protective devices can operate when an electrical fault occurs. An undersized grounding conductor may not perform as intended under fault conditions.
Grounding design should also consider conductor material, connection methods, equipment requirements, available fault current and the electrical regulations that apply to the installation.
Ground Wire Size Calculator FAQs
Enter the rating of the circuit breaker or fuse. The calculator compares that value with its grounding conductor reference table and returns the corresponding wire size.
Equipment grounding conductor sizing is commonly related to the rating of the overcurrent protective device rather than simply the normal load current.
In many installations the equipment grounding conductor may be smaller than the current-carrying conductors, but its permitted size depends on applicable electrical rules and the circuit protection rating.
Not necessarily. Copper and aluminum conductors can require different sizes, which is why the calculator includes a material selector.
This calculator is intended primarily as an equipment grounding conductor reference. Grounding electrode conductors and service grounding may use different sizing rules.