Conductor Area Comparison
VisualBars show circular-mil area (NEC Chapter 9, Table 8). The minimum threshold is marked on your EGC bar.
Grounding Path Diagram
EGC vs GEC
DistinctionEGC — Equipment Grounding
- Effective ground-fault current return path
- Base size from Table 250.122 by OCPD, then adjusted
- Runs with the circuit conductors
- Helps the OCPD clear a fault
GEC — Grounding Electrode
- Connects system to the grounding electrode
- Sized per Table 250.66
- At service / separately derived system
- Normally not a load-current conductor
Why This Matters
FoundationThe EGC is part of the effective ground-fault current path. During a fault it must carry enough current to operate the OCPD quickly — before someone is hurt or equipment is damaged. An undersized or discontinuous EGC may not clear the fault fast enough, or at all.
The base wire-type EGC size is selected from Table 250.122 by the OCPD rating — not the load and not the phase-conductor size alone — then adjusted for applicable rules such as proportional upsizing, parallel installations, multiple circuits, motor circuits, and the effective ground-fault current path requirement.
Step-by-Step Calculation Trace
DeterministicEvery value below is derived from your inputs. Nothing is hidden.
Assumptions & Limits
Transparency- •Base wire-type EGC from NEC Table 250.122 using the smallest row ≥ the OCPD rating.
- •Circular-mil values are exact (NEC Chapter 9, Table 8). The 250.122(B) ratio is not rounded before selecting a standard size, and the selection ladder is restricted to real Chapter 9 Table 8 conductor sizes.
- •Exact mathematical sizing is conservative; AHJ / qualified-person interpretations may differ where rounding is considered. The 250.122(B) Exception (2020+) permits a qualified person to size for an effective ground-fault current path per 250.4(A)(5)/(B)(4) instead.
- •The 250.122(A) “need not exceed the circuit conductors” cap is applied only when EGC and phase materials match; otherwise it is left to engineering / AHJ review.
- •This tool does not verify circuit-conductor ampacity. It never checks the phase conductors against 240.4 / 310.16. A capped or “passing” result says nothing about whether the circuit conductors themselves are legally sized.
- •Wire-type EGCs only; raceway/armor continuity, terminations, and fault-current adequacy are not evaluated.
Sizing Result
—Comparison Table
| Parameter | Value |
|---|
Adequacy Gauge
VisualOCPD-to-EGC Mapping
Table 250.122The row used for your OCPD is highlighted.
| OCPD not exceeding (A) | Copper | Aluminum / Cu-clad Al |
|---|
Challenges use the same computeEGC() engine as the main calculator (NEC 2023 method, exact circular-mil sizing). Your score updates live from the current field values.
Size the EGC
A 100 A breaker protects a feeder with 1 AWG copper phase conductors. What is the minimum copper wire-type EGC?
Upsized Phase Conductor
A 60 A circuit requires minimum 6 AWG copper phase conductors, but you install 4 AWG for voltage drop. Using exact circular-mil sizing, what minimum copper wire-type EGC should you use?
Parallel Feeders (Separate Raceways)
A 400 A feeder uses 2 parallel sets of 3/0 AWG copper in separate raceways. How many wire-type EGCs do you need, and what size (copper)?
EGC or GEC?
Match the scenario to the correct conductor type:
Design a Complete EGC Installation
200 A feeder, aluminum phase conductors, 3 parallel sets in separate raceways, phase conductors upsized from 4/0 AWG to 250 kcmil for voltage drop. Size the wire-type EGC for each raceway.
Challenge Score
NEC Reference Panel
NEC 2023Article 250 — Grounding and Bonding
Article 250 governs grounding and bonding. Wire-type EGC sizing is in 250.122 / Table 250.122.
| Section | Topic | Paraphrased Logic |
|---|
Edition Notes
What Is an EGC?
An equipment grounding conductor connects non-current-carrying metal parts of equipment back to the system grounding point, forming part of the effective ground-fault current path. During normal operation it is normally not a load-current conductor. During a ground fault it must carry enough current to help operate the OCPD.
It is a safety path that exists for fault and abnormal conditions.
How EGC Sizing Actually Works
The base wire-type EGC size is selected from Table 250.122 by the OCPD rating. That base is then adjusted for applicable rules — proportional upsizing (250.122(B)), parallel installations (250.122(F)), multiple circuits (250.122(C)), motor circuits (250.122(D)), and the overriding requirement to maintain an effective ground-fault current path (250.4(A)(5)).
Larger OCPD generally means more available fault energy and a larger base EGC — but the OCPD row is the starting point, not the whole story.
Motor Circuits · 250.122(D)
For motor circuits the EGC is sized from Table 250.122 using the rating of the branch-circuit short-circuit and ground-fault protective device (selected per 430.52), which is often much larger than the conductor ampacity would suggest. This tool does not model 430.52 device selection.
Multiple Circuits · 250.122(C)
Where several circuits share one raceway, cable, trench, or cable tray, a single EGC sized for the largest OCPD among them is permitted to serve them all. This is a permissive allowance — it never requires a smaller conductor than 250.122 would otherwise demand.
Upsizing & EGC
250.122(B)When phase conductors are increased in size (often for voltage drop), a wire-type EGC that is installed must be increased proportionally by circular-mil area. In the 2020 and later editions this does not apply where the increase is only to satisfy the ampacity adjustment/correction factors of 310.15(B)/(C).
This tool selects the smallest standard Chapter 9 Table 8 conductor whose area is ≥ the exact required cmil (it does not round the ratio down). Exact sizing is conservative; some AHJs accept documented rounding methods.
Exception (2020+)
A qualified person is permitted to size the EGC to provide an effective ground-fault current path in accordance with 250.4(A)(5)/(B)(4) instead of the strict circular-mil method. This tool always applies the strict circular-mil method.
Parallel Conductors
250.122(F)Where conductors run in separate raceways or cables, a wire-type EGC is installed in each raceway/cable, each sized per Table 250.122 from the feeder/branch-circuit OCPD — not divided among the sets (250.122(F)(1)(b)).
Where parallel conductors share a single raceway, auxiliary gutter, or cable tray, a single wire-type EGC sized by the OCPD is permitted (250.122(F)(1)(a)). Where a wire EGC is installed in a cable tray it must also meet the minimum in 392.10(B)(1)(c), per 250.122(F)(1)(c). A qualifying metal raceway may itself serve as the EGC under 250.122(F)(1)(d) and 250.118.
Multiconductor cable assemblies each contain their own EGC sized per 250.122 (250.122(F)(2)). Where paralleled multiconductor cables share one raceway, auxiliary gutter, or cable tray, a single combined EGC is permitted per 250.122(F)(2)(c). The 250.122(A) sectioned-EGC allowance also permits an EGC to be run in sections where the wiring method allows.
Common Mistakes
AvoidSizing by load current instead of OCPD
A 20 A breaker on a 12 A load still bases the EGC on the 20 A OCPD row.
Confusing EGC with GEC
Different conductors, different tables (250.122 vs 250.66), different purposes.
Wrong material column
Table 250.122 has separate copper and aluminum/Cu-clad-Al columns. Using the wrong one undersizes the EGC.
Rounding the 250.122(B) ratio down
A result just above a standard size (e.g. 16,511 cmil vs 16,510 for 8 AWG) requires the next size up under exact sizing.
Splitting one EGC among separate raceways
Each separate raceway gets its own full-size EGC per 250.122(F).
Reading the 250.122(A) cap as a pass on the circuit conductors
“The EGC need not be larger than the circuit conductors” assumes those conductors are themselves legally sized for the OCPD under 240.4 / 310.16. Capping an EGC to an illegally small phase conductor is not compliance.
EGC vs GEC — Detail
| Attribute | EGC | GEC |
|---|---|---|
| Full Name | Equipment Grounding Conductor | Grounding Electrode Conductor |
| Sizing Table | Table 250.122 (base, then adjusted) | Table 250.66 |
| Sized By | OCPD rating (base) | Largest ungrounded service/derived conductor |
| Location | With circuit conductors | Service / separately derived system |
| Purpose | Effective ground-fault current path; helps clear faults | Connects system to earth electrode(s) |
| Current | Normally none; carries fault current during ground faults | Normally not a load-current conductor; may carry current under lightning, surge, ground-fault, or abnormal conditions |
Equipment grounding conductors are sized by code logic and the effective-path requirement — not by wishful symmetry.
In-File Test Harness
DeterministicThese assertions run against the same computeEGC() engine used by the calculator and challenges. They run on load; use the buttons to re-run. Results also print to the browser console.
| # | Test | Expected | Actual | Result |
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