# GroundLoop: Earth Ground Test — NEC rod sizing & resistivity

> NEC rod sizing & resistivity (iPhone/iPad app by 毅 王.)

- Source: https://appshunter.io/ios/app/groundloop-earth-ground-test/id6779190914 (this page in markdown: same URL + `.md`)
- Developer: [毅 王](https://appshunter.io/developer/6774631380)
- Category: Productivity
- Price: Free with in-app purchases
- Age rating: 4+
- Requires: iOS 17.0 · 2 MB
- Languages: American English
- Released: 2026-06-16
- Data updated: 2026-07-17
- User reviews in markdown: https://appshunter.io/ios/app/groundloop-earth-ground-test/id6779190914/reviews.md

## What is GroundLoop?

GroundLoop is the grounding field companion for electrical engineers, contractors, and tower techs — fully offline, no account, no subscription.

SOIL RESISTIVITY
Enter Wenner four-pin or Schlumberger readings and get apparent resistivity per spacing instantly, with probe-depth correction, anomaly flags for layered soil, and a resistivity-vs-spacing curve you can read at the truck.

ELECTRODE ESTIMATES
Size a single rod, a multi-rod array, or a grid (Sverak screening formula) and compare against your target — 25 ohms (NEC 250.53), 5 ohms, or a custom spec. Every result shows the formula reference it came from.

FALL-OF-POTENTIAL TESTS
Enter your current-probe distance and GroundLoop lays out the 52/62/72% voltage-probe positions, then checks your three readings for a valid plateau — so a bad test gets caught in the field, not back at the office.

FIELD REPORTS
Export a clean PDF per site: resistivity tables, electrode estimates with formula references, fall-of-potential records, and date — ready for your project file.

FREE TO TRY
One site with every tool unlocked, reports watermarked. One-time purchase removes the watermark and the site limit. No subscription, ever.

GroundLoop is a field calculation and recording aid. It encodes textbook formulas with cited references (values pending professional-engineer review are labeled in-app); it is not a substitute for a licensed PE's design, the governing standard, or required field verification.

## Pricing and in-app purchases

Base price: Free.

**One-time purchases**

| Purchase | Price | Type |
| --- | --- | --- |
| GroundLoop Unlock | $19.99 | one-time |



## Version history (last 2 releases)

### 1.1 — 2026-06-27

• Refined the App Store listing and search keywords so the right pros can find the app
• Performance and stability improvements

### 1.0 — 2026-06-16

No release notes.

## More apps by 毅 王

- [Luthier Repair Card](https://appshunter.io/ios/app/luthier-repair-card/id6775381985)
- [GroomSpec: Dog Grooming Guide](https://appshunter.io/ios/app/groomspec-dog-grooming-guide/id6778254427)
- [HeatTreatBench: Knife Steels](https://appshunter.io/ios/app/heattreatbench-knife-steels/id6778304658)
- [Rocket Calculator: ApogeeField](https://appshunter.io/ios/app/rocket-calculator-apogeefield/id6778329350)
- [PourLog: Concrete Test Log](https://appshunter.io/ios/app/pourlog-concrete-test-log/id6778377971)

All apps by 毅 王: https://appshunter.io/developer/6774631380

## Related topics

[grounded labs](https://appshunter.io/ios/topics/grounded-labs)

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-07-17.*