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Aluminum Equipment Grounding Conductor Size Calculator (NEC Table 250.122, Aluminum Column)

Size an aluminum EGC.

Inputs

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ℹ️The equipment grounding conductor's own material — not necessarily the same as the circuit's ungrounded conductors. Table 250.122 uses genuinely different size boundaries for copper and aluminum — aluminum EGCs run one to two sizes larger than the equivalent copper size.

A

ℹ️The rating or setting of the automatic overcurrent device (breaker or fuse) protecting the circuit ahead of the equipment — not the ampacity of the circuit conductors themselves. Common standard sizes: 15, 20, 30, 40, 60, 100, 150, 200, 400A, up to 6000A for large services — an adjustable-trip breaker's actual setting (e.g. 201A) works too, since Table 250.122 keys off the OCPD's "rating or setting," not just standard sizes.

Ungrounded Conductors Upsized?

Increased for Voltage Drop or Another Reason?

Cost

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Required Equipment Grounding Conductor: 4 AWG (Aluminum)

Sized directly from NEC Table 250.122, no proportional increase applies

NEC Table 250.122 Lookup

OCPD (breaker/fuse) rating: 200 A

Table row: Over 100 through 200 A

Table-derived EGC size: 4 AWG

250.122(B) Upsize Check

Not checked — enable the upsize toggle if ungrounded conductors were increased for voltage drop or another reason

Assumptions Used

NEC Table 250.122 (minimum size equipment grounding conductors), NEC 250.122(B) proportional increase where ungrounded conductors are upsized. Assumes a single, homogeneous conductor material for both the ungrounded conductors and the EGC, and a single (non-parallel) raceway or cable run. This is a reference estimate — confirm against the code edition adopted in your jurisdiction and a licensed electrician before final installation.

Want the full walkthrough on Table 250.122, the 250.122(B) upsize rule, and how this differs from grounding electrode conductor sizing? Equipment Grounding Conductor Sizing Guide →

Equipment Grounding ConductorPanel200 AUngrounded conductor (OCPD-protected)4 AWGEquipmentFault current returns via the EGC — not through earthDiagram simplified for clarity (not to scale)

Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete Equipment Grounding Conductor Size Calculator.

Aluminum equipment grounding conductor sizing

Table 250.122 provides a full aluminum/copper-clad aluminum column, generally running one to two AWG sizes larger than the equivalent copper size at the same OCPD rating.

This page defaults to aluminum at a 200A OCPD rating — edit the inputs above to match your actual circuit.

  • Aluminum EGC sizing uses a separate table column, not a simple multiple of the copper sizes.
  • Unlike the grounding electrode conductor, there's no direct-earth-contact restriction specific to the equipment grounding conductor itself.
  • General conductor installation rules — terminal temperature ratings, listed connectors, corrosion protection at connections — still apply to aluminum EGCs.

Equipment Grounding Conductor Formula: How Is the Size Determined?

Two steps: a direct NEC Table 250.122 lookup from the OCPD rating, then a 250.122(B) proportional-increase check.

Step 1 — Table 250.122 Lookup

Find the Table 250.122 row whose OCPD-rating range contains the circuit's breaker/fuse rating

Table EGC Size = that row's EGC size, for the selected material (Cu or Al)

Table 250.122 has 19 rows, each covering a range of overcurrent device ratings, with separate copper and aluminum/copper-clad aluminum columns — sized from the OCPD rating, not the ampacity of the circuit conductors themselves.

Step 2 — 250.122(B) Proportional Increase

If ungrounded conductors were increased for voltage drop (or another reason besides temperature/conductor-count derating):

Ratio = Actual Installed Ungrounded Conductor CM ÷ Minimum Required Ungrounded Conductor CM

Final EGC = next standard size ≥ (Table EGC Size CM × Ratio), never larger than the ungrounded conductor itself

A 2020+ NEC exception also permits a qualified person to determine an alternative EGC size using engineering judgment instead of the strict circular-mil proportion — that professional-judgment path isn't modeled here, since it depends on site-specific analysis this calculator can't perform.

Worked Example

This example walks through your current inputs above, using the same steps as the Formula section.

Input Values Used

InputValueWhy it is used
OCPD rating200 ASets the Table 250.122 row
EGC materialAluminumSets the Table 250.122 column
Ungrounded conductors upsized?NoDetermines whether the 250.122(B) proportional increase applies

Step 1 — Table 250.122 Lookup

CalculationResult
Table rowOver 100 through 200 A
Table-derived EGC size4 AWG

Step 2 — 250.122(B) Upsize Check

CalculationResult
Upsize checkNot checked — ungrounded conductors not marked as upsized
Final recommended size4 AWG (aluminum)

Therefore, for a 200 A circuit, you need approximately 4 AWG aluminum for the equipment grounding conductor.

Related Calculators

Grounding Electrode Conductor Size CalculatorWire Size Calculator

Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.

FAQ

Yes — Table 250.122 provides a full aluminum/copper-clad aluminum column for EGC sizing, generally one to two AWG sizes larger than the equivalent copper size at the same OCPD rating.
No — that restriction (NEC 250.64(A)) is specific to grounding electrode conductors connecting to earth/masonry. It doesn't directly apply to equipment grounding conductors, which typically stay within equipment, raceways, and panels rather than connecting to earth.
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