Equipment Grounding Conductor Sizing

Size the equipment grounding conductor (EGC) per NEC §250.122 based on circuit breaker/fuse rating. Includes parallel conductor rules (§250.122(F)) and voltage drop upsizing (§250.122(B)).

NEC edition

Inputs

sets

For parallel conductors: EGC sized from full OCPD rating, then one per set

§250.122(B): if phase conductors are upsized for voltage drop, EGC must be proportionally upsized

Original minimum phase conductor before upsizing

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⚡ Test your knowledge
NEC Article 220 was renumbered in the 2026 code cycle. What is the new article number?
  • A. Art. 100
  • B. Art. 120
  • C. Art. 200
  • D. Art. 230
💡 NEC 2026 renumbered Article 220 (Branch-Circuit, Feeder, and Service Calculations) to Article 120.
Energy Management Systems were moved from Article 750 to which article in NEC 2026?
  • A. Art. 100
  • B. Art. 125
  • C. Art. 130
  • D. Art. 150
💡 NEC 2026 moved Energy Management Systems from Article 750 to Article 130.
Which NEC standard size overcurrent device comes after 90A?
  • A. 95A
  • B. 100A
  • C. 110A
  • D. 105A
💡 Per NEC §240.6(A), the standard sizes are …90, 100, 110, 125… There is no 95A standard size.

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How it works & the NEC rules behind it

An Equipment Grounding Conductor (EGC) provides a low-impedance ground-fault return path to trip the upstream circuit breaker or fuse quickly during a short circuit or ground fault, preventing dangerous electrical shock and fire hazards.

Critical Code Rules for EGC Sizing (§250.122):

  • Sized from Overcurrent Device: Unlike phase conductors (which are sized from calculated load), the EGC is strictly sized from the rating of the upstream fuse or circuit breaker protecting the circuit per Table 250.122.
  • Proportional Upsizing for Voltage Drop (§250.122(B)): If the ungrounded (phase) conductors are increased in size for voltage drop or distance, the EGC must be increased in size proportionally according to the circular mil area increase!
  • Parallel Conductor Runs (§250.122(F)): When conductors are run in parallel in separate raceways or cables, a full-sized EGC based on the total circuit OCPD rating must be installed in each parallel raceway.

Formulas & equations

Base EGC Size = Lookup in NEC Table 250.122 based on OCPD (Amps) Proportional Upsize Area = Base EGC Area (kcmil) × (Installed Phase kcmil / Minimum Phase kcmil)
Where:
• Installed Phase kcmil: Cross-sectional area of upsized wire.
• Minimum Phase kcmil: Minimum wire size required solely for ampacity prior to upsizing.

NEC reference table

Rating of Overcurrent Device (OCPD) Minimum Copper EGC Size Minimum Aluminum EGC Size
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 AWG250 kcmil

*Source: NEC Table 250.122 (Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment).

Worked example, step by step

Example Calculation: EGC for a 100A Subpanel with Upsized Phase Conductors

Scenario: A 100A subpanel is fed 250 feet away. Due to voltage drop, the phase conductors were upsized from the minimum required #4 AWG Cu (41.74 kcmil) to #1 AWG Cu (83.69 kcmil).

  • Step 1 (Base EGC): For a 100A breaker, Table 250.122 requires a base size of #8 AWG Copper (16.51 kcmil).
  • Step 2 (Upsize Ratio): Ratio = 83.69 kcmil / 41.74 kcmil = 2.005 (200.5%).
  • Step 3 (Proportional EGC Area): 16.51 kcmil × 2.005 = 33.10 kcmil.
  • Step 4 (Select Conductor): Looking at Chapter 9 Table 8, #6 AWG Cu is 26.24 kcmil (too small); #4 AWG Cu is 41.74 kcmil (sufficient).
  • Result: Install #4 AWG Copper EGC per §250.122(B).

Frequently asked questions

Yes. In fact, for circuits 30A and larger, the equipment grounding conductor from Table 250.122 is almost always significantly smaller than the phase conductors because it is designed to carry fault current only momentarily until the breaker trips.

Yes, under NEC §250.118, rigid metal conduit (RMC), intermediate metal conduit (IMC), and electrical metallic tubing (EMT) with approved fittings are recognized as equipment grounding conductors without requiring a separate internal green wire (unless specified by project engineers or local healthcare/hazardous code rules).

An **EGC (Equipment Grounding Conductor)** bonds non-current-carrying metal parts of equipment back to the electrical panel to trip the circuit breaker during a ground fault. A **GEC (Grounding Electrode Conductor)** connects the electrical service neutral/grounding bar to the earth via ground rods, water pipes, or concrete-encased Ufer electrodes per §250.66.

The equipment grounding conductor is sized from Table 250.122 by the rating of the circuit breaker or fuse protecting the circuit — not by the ampacity of the phase conductors. A 20A circuit needs at least a #12 AWG copper EGC, a 100A circuit needs #8 AWG, and a 200A service needs #4 AWG. Enter your OCPD rating above for the exact minimum, including parallel-run and upsizing adjustments.

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