Grounding Conductor Size Calculator

Size equipment grounding conductor per NEC Table 250.66 and NEC Table 250.122 for grounding electrode and equipment grounding conductors.

Related Calculators

How to Size Grounding Conductors per NEC

GEC vs EGC — What Is the Difference?

The Grounding Electrode Conductor (GEC) connects the grounding electrode (ground rod, water pipe, concrete-encased rebar, etc.) to the grounding terminal of the service disconnect. It is sized per NEC Table 250.66 based on the largest service-entrance conductor. The Equipment Grounding Conductor (EGC) provides a fault-current path from equipment to the source and is sized per NEC Table 250.122 based on the overcurrent protection device rating.

NEC Table 250.66 — GEC Sizing

Rule: GEC size depends on the largest service-entrance conductor and the type of grounding electrode.

For ground rod, pipe, or plate electrodes: GEC need not exceed 6 AWG copper per NEC 250.66(A). For concrete-encased or ground ring electrodes: use the full Table 250.66 lookup.

NEC Table 250.122 — EGC Sizing

The EGC is sized based on the rating of the overcurrent protective device ahead of the equipment. For a main service, this is typically the main breaker rating. Common sizes: 100A → 8 AWG, 200A → 6 AWG, 400A → 3 AWG.

Worked Examples

Scenario 1: 200A service with a ground rod electrode.

Electrode type: Ground rod → NEC 250.66(A) caps GEC at 6 AWG Copper
EGC from Table 250.122 at 200A OCPD → 6 AWG Copper

Scenario 2: 200A service with a concrete-encased electrode.

Estimated service conductor: 2/0 AWG (for 101-200A)
NEC 250.66 table: 2/0 or 3/0 AWG conductor → 4 AWG Copper GEC

Practical Tips

Ground rod/pipe/plate electrodes have a hard cap of 6 AWG copper — you never need a larger GEC for these electrode types, regardless of service size.
Concrete-encased (ufer) and ground ring electrodes require larger GECs for higher service sizes, as they follow the full Table 250.66.
The GEC minimum is 8 AWG copper per NEC 250.66 — but this only applies to non-rod electrodes.
When multiple grounding electrodes are present, the GEC is sized to the largest electrode's requirement.

Code References

NEC 250.66, NEC 250.122, NEC 250.54

Frequently Asked Questions

What is the difference between GEC and EGC?

The Grounding Electrode Conductor (GEC) connects the grounding electrode (rod, pipe, ring) to the service grounding terminal. The Equipment Grounding Conductor (EGC) bonds non-current-carrying metal parts of equipment to the source. They serve different purposes and are sized by different NEC tables.

Why is the GEC limited to 6 AWG for ground rods?

NEC 250.66(A) recognizes that a single ground rod has high impedance regardless of conductor size. Using a conductor larger than 6 AWG copper to a single rod provides negligible improvement in fault current capability, so the code limits it to avoid waste.

Does aluminum wire qualify for grounding conductors?

Yes, but aluminum GECs must be at least 6 AWG per NEC 250.66(B). Aluminum is not permitted for equipment grounding conductors smaller than 8 AWG per NEC 250.120. This calculator assumes copper conductors.

When should I use the concrete-encased (ufer) electrode type?

Concrete-encased electrodes (also called ufer grounds) use reinforcing steel or a copper conductor embedded in the building foundation concrete. They are found at the footing or foundation of new construction. This type is very effective due to the large surface area contact with earth.