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Grounding & Bonding Conductor Calculator

Size Equipment Grounding Conductors (EGC) per NEC Table 250.122 and Grounding Electrode Conductors (GEC) per NEC Table 250.66 with special electrode cap rules.

⚡ NEC 2023 Code Basis & Electrical Safety Disclaimer

Based on NEC 2023 (same as 2020 & 2017 Article 250). Estimates for planning only — electrical installations must comply with local code editions and be performed/verified by a licensed electrician. Not a substitute for engineered design or an AHJ ruling.

🔰 Grounding & Bonding System Schematic
Grounding System SchematicDiagram showing main service panel, neutral bus, main bonding jumper, EGC to equipment frame, and GEC to earth electrode.

Grounding Conductor Results

Required Grounding Wire Size
8 AWG Cu
NEC Table 250.122 Lookup
Conductor Application
EGC Equipment Ground
Branch/Feeder Fault Protection
Protection Basis / Service Size
100 A OCPD
Up to 100 Ampere Device
Special Code Provision / Cap
Full Table Standard
No Cap Applied

Worked Examples: Grounding Sizing (EGC & GEC)

Review two fundamental grounding sizing examples:

  • Example 1 (EGC for 100A & 200A Feeders):
    • For a 100 A feeder breaker, NEC Table 250.122 specifies a minimum 8 AWG Copper (or 6 AWG Aluminum) equipment grounding conductor.
    • For a 200 A feeder breaker, NEC Table 250.122 specifies a minimum 6 AWG Copper (or 4 AWG Aluminum) EGC.
  • Example 2 (GEC for 2/0 AWG Copper Service):
    • For a 200 A service entrance with 2/0 AWG copper ungrounded conductors, NEC Table 250.66 specifies a minimum 4 AWG Copper grounding electrode conductor (GEC).
    • If the GEC connects solely to a ground rod electrode, NEC 250.66(A) caps the required size at 6 AWG Copper.

Engineering Code & Reference Citations

  • NFPA 70 / NEC Table 250.122: Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment. nfpa.org
  • NFPA 70 / NEC Table 250.66: Grounding Electrode Conductor for Alternating-Current Systems. nfpa.org
  • NFPA 70 / NEC Section 250.66(A)-(C): Connections to Rod, Pipe, Plate, and Concrete-Encased Electrodes. nfpa.org

Frequently Asked Questions (FAQ)

What EGC copper wire size is required for a 100 Amp circuit?

Per NEC Table 250.122, an overcurrent protective device (OCPD) rated 100 Amperes requires a minimum Equipment Grounding Conductor (EGC) size of 8 AWG copper (or 6 AWG aluminum).

What EGC copper wire size is required for a 200 Amp circuit?

Per NEC Table 250.122, a 200 Ampere overcurrent device requires a minimum Equipment Grounding Conductor (EGC) size of 6 AWG copper (or 4 AWG aluminum).

What GEC size is required for a 2/0 AWG copper service entrance?

Per NEC Table 250.66, for a service with 2/0 AWG or 3/0 AWG copper ungrounded conductors, the Grounding Electrode Conductor (GEC) must be a minimum of 4 AWG copper (or 2 AWG aluminum).

What is the maximum required GEC size to a ground rod or pipe electrode?

Under NEC 250.66(A), where the grounding electrode conductor connects solely to a rod, pipe, or plate electrode, that portion of the conductor is not required to be larger than 6 AWG copper (or 4 AWG aluminum).

What is the maximum required GEC size to a concrete-encased (Ufer) electrode?

Under NEC 250.66(B), where the grounding electrode conductor connects solely to a concrete-encased electrode (Ufer ground), that portion of the conductor is not required to be larger than 4 AWG copper.

What is the difference between EGC and GEC in the NEC?

An Equipment Grounding Conductor (EGC) connects non-current-carrying metal parts of equipment back to the system grounded conductor at the panel to facilitate circuit breaker tripping during a ground fault (NEC Table 250.122). A Grounding Electrode Conductor (GEC) connects the grounded system conductor to earth via electrodes (rod, water pipe, Ufer) to limit voltage surges and stabilize system voltage (NEC Table 250.66).

How does upsizing ungrounded conductors for voltage drop affect EGC sizing?

Under NEC 250.122(B), if ungrounded circuit conductors are increased in size (e.g. for voltage drop compensation), the equipment grounding conductor must be increased in size proportionally according to the circular-mil area ratio of the ungrounded conductors.

What EGC copper wire size is required for a 60 Amp breaker?

Per NEC Table 250.122, a 60 Ampere overcurrent device requires a minimum 10 AWG copper (or 8 AWG aluminum) equipment grounding conductor.

What EGC copper wire size is required for a 400 Amp circuit?

Per NEC Table 250.122, a 400 Ampere overcurrent device requires a minimum 3 AWG copper (or 1 AWG aluminum) equipment grounding conductor.

What GEC size is required for a 400 kcmil copper service conductor?

Per NEC Table 250.66, for service conductors over 350 through 600 kcmil copper, the required GEC is 1/0 AWG copper (or 3/0 AWG aluminum).

Is aluminum allowed for grounding electrode conductors outdoor near earth?

Under NEC 250.64(A), aluminum or copper-clad aluminum GECs cannot be used where exposed to corrosive conditions or where in direct contact with earth or masonry within 18 inches (450 mm) of the earth.

Are NEC 250.66 and 250.122 grounding values identical across NEC 2017, 2020, and 2023?

Yes. The minimum sizing tables 250.66 and 250.122 have remained completely unchanged across the 2017, 2020, and 2023 editions of NFPA 70.