Grounding Conductor Size Chart

Minimum equipment grounding conductor sizes by the rating of the overcurrent device ahead of the equipment, in copper and aluminium.

Page last changed 2026-10-19 · based on NEC 2023 (NFPA 70-2023)

Minimum Equipment Grounding Conductor (NEC Table 250.122)

The equipment grounding conductor is sized from the overcurrent device rating, not from the phase conductors. That is deliberate: its job is to carry fault current long enough for the overcurrent device to open, and that current is set by the device, not by the conductor ampacity.

The consequence is counter-intuitive — the grounding conductor can be much smaller than the phase conductors, and it does not need to be increased just because the phases were upsized for voltage drop.

That last point has a real exception. Where the phase conductors are increased in size to limit voltage drop, the grounding conductor must be increased proportionally. It is an easy requirement to miss, and it is why a long feeder with upsized phases may need a larger equipment ground than the table shows.

Why It Can Be Smaller Than the Phase Conductors

The phase conductors must carry the load current continuously without overheating. The grounding conductor carries current only during a fault, and only for as long as it takes the overcurrent device to open — milliseconds to a few seconds.

Its sizing therefore comes from a different question: can it carry the available fault current for that duration without being destroyed, and is its impedance low enough that the fault current actually trips the device? Both are satisfied by a conductor much smaller than the phases.

The proportional-increase rule exists because that second condition can fail. A long feeder has enough impedance to limit fault current, and if the phases are upsized for voltage drop the ground path may be left relatively too small — so the Code requires the ground to grow with them.

Frequently Asked Questions

How do I size an equipment grounding conductor?

From the rating of the overcurrent device ahead of the equipment, using NEC Table 250.122. A 100 A device needs a #8 copper equipment ground, a 400 A device a #3, and a 2000 A device a 250 kcmil. The phase conductor size is not used for this.

Can the grounding conductor be smaller than the phase conductors?

Usually yes, and often much smaller. It carries current only during a fault, so it is sized to survive the fault and to trip the device rather than to carry load continuously. The exception is when the phase conductors are upsized for voltage drop — then the ground must be increased proportionally.

What is the minimum size grounding conductor?

For a 15 A circuit it is #14 copper, for 20 A it is #12, and for 30 A through 60 A it is #10. It does not go below #14 copper in the table, and a larger circuit cannot be given a smaller ground than its device rating calls for.

Does the grounding conductor have to be in the same raceway?

It must be run with the circuit conductors, in the same raceway, cable or trench. Separating it creates a loop with a different impedance and can cause circulating currents and unpredictable fault paths.

What is the difference between grounding and bonding?

Grounding connects the system to earth; bonding connects conductive parts to each other so they stay at the same potential. The equipment grounding conductor does both jobs — it bonds the equipment enclosure to the system and provides the fault path that trips the breaker.

Related

• Breaker Sizes Chart
• Wire Ampacity Chart
• Cable Sizes
• Motor Full-Load Current
• Voltage Drop Calculator

Value Sources

References and calculation methods used for this page are listed below. Numbered markers connect table columns where present. A reference listing does not itself establish that every value has been independently checked.

Data Sources

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No page-specific independent source review is recorded here. The listed references and formulas explain the basis of the compilation; automated consistency checks do not verify the original sources or establish product conformity.

Sizes are the minimum permitted. Where phase conductors are increased for voltage drop, the equipment grounding conductor must be increased proportionally. The requirements for specific equipment — swimming pools, agricultural buildings, separately derived systems — modify the general table.

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