Equipment Grounding Conductor (EGC) Sizing Calculator

The equipment grounding conductor is the safety conductor that carries fault current from equipment enclosures back to the source neutral bond point — and sizing it correctly under NEC Section 250.122 is more nuanced than a simple table lookup when phase conductors are derated, feeders run in parallel, or the raceway serves as the EGC path. This calculator handles the full 250.122 logic tree: select the OCPD rating (15 A through 6000 A) and the tool returns the minimum EGC size from NEC Table 250.122. If the phase conductor was upsized beyond what ampacity alone requires (for voltage drop or other reasons), Section 250.122(B) requires the EGC to be upsized proportionally — this is modeled explicitly. For parallel feeders under 250.122(F), EGC requirements differ depending on whether conductors run in the same raceway, multiple separate raceways, or multiconductor cables — all three configurations are supported. Metal raceway and cable armor serving as the EGC path is also evaluable. The Results tab shows the sized EGC with an Adequacy Gauge and OCPD-to-EGC mapping table. The visual Grounding Path Diagram illustrates the EGC current flow from equipment back to source. A Conductor Area Comparison chart shows EGC vs. phase conductor cross-section. The Learn tab includes an EGC vs. GEC explainer — a critical distinction that is routinely confused — and covers all four special cases: upsizing 250.122(B), parallel 250.122(F), raceway/cable path, and material-mismatch cap. A Design Challenge tab and a Self-Test tab (deterministic calculation harness) are included. Supports NEC 2017, 2020, and 2026.

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A live look at the app you'll launch — every control on the left drives the visualizations on the right in real time.

Example data — not a real field report

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• 01Look up the minimum EGC size from NEC Table 250.122 given a known OCPD rating and explain why EGC sizing is based on OCPD rather than load current
• 02Apply the NEC 250.122(B) proportional upsizing rule when a phase conductor has been increased beyond minimum ampacity and calculate the required EGC adjustment
• 03Determine the EGC requirement for a parallel feeder under 250.122(F) for each of the three parallel configurations: same raceway, separate raceways, and multiconductor cables
• 04Evaluate whether a metal raceway or cable armor qualifies as the EGC path and identify when a supplemental wire EGC is also required
• 05Explain the difference between an EGC (250.122) and a GEC (250.66) — what each connects, what NEC section governs each, and why they serve different safety functions
• 06Identify the material-mismatch cap condition and explain what happens when a copper OCPD protects an aluminum EGC at certain sizes

• —Not a design document, stamped calculation, or approval record.
• —Not a substitute for engineering analysis by a licensed professional.
• —Not a reproduction of NEC tables — values are computed and cited, and you must verify against the code edition enforced in your jurisdiction.
• —Not connected to live equipment and not a safety device.