# Voltbox: PV Installer Toolkit — NEC 690/705 PV Calculators

> NEC 690/705 PV Calculators (iPhone/iPad app by GABRIELE CHESI.)

- Source: https://appshunter.io/ios/app/voltbox-pv-installer-toolkit/id6798591811 (this page in markdown: same URL + `.md`)
- Developer: [GABRIELE CHESI](https://appshunter.io/developer/6793043905)
- Category: Utilities
- Price: Free with in-app purchases
- Age rating: 4+
- Requires: iOS 15.0 · 20 MB
- Languages: American English
- Released: 2026-08-18
- Data updated: 2026-09-19
- User reviews in markdown: https://appshunter.io/ios/app/voltbox-pv-installer-toolkit/id6798591811/reviews.md

## What is Voltbox?

Voltbox: PV Installer Toolkit is a professional calculator toolkit for solar/PV installers, built around NEC Articles 690 and 705. Fast, accurate, and yours to own — pay once, keep it forever.

12 CALCULATORS

Array & String Design (free)
• String Sizing — max modules per string, temperature-corrected (NEC 690.7)
• PV Circuit Sizing — conductor & OCPD sizing for source circuits (NEC 690.8/690.9)

Interconnection & Safety
• 120% Rule — backfeed breaker vs. busbar interconnection check (NEC 705.12)
• Rapid Shutdown — array boundary & voltage/time limits reference (NEC 690.12)
• DC Arc-Fault Protection — whether 690.11 AFCI protection applies to your install

Circuit Installation
• Voltage Drop — DC array-to-inverter run (NEC Ch. 9 Table 8)
• Conduit Fill — DC source/output conductors in conduit (NEC Ch. 9 Table 1)
• Grounding & Bonding — GEC (690.47) and EGC (690.43/250.122) sizing
• AC Output Sizing — inverter output circuit conductor & OCPD (NEC 690.8)
• Rooftop Temp Adder — ambient temperature correction for rooftop conduit (NEC 310.15(B)(3)(c))

Storage & Estimates
• Battery Sizing — ESS backup capacity from critical load & duration
• Production Estimate — quick annual output ballpark from peak sun hours

WHY VOLTBOX
• One-time purchase for Pro — never a subscription, never a recurring fee
• Save and organize calculations by project
• Built for the job site: fast, no clutter, no login screens, works with no signal
• No account required — open the app and start calculating

String Sizing and PV Circuit Sizing are free. Unlock Pro once to get every other calculator.

Voltbox is a reference tool based on the NEC. Always verify results against the current code edition adopted in your area and confirm compliance with a licensed electrician or installer before performing any installation.

## Pricing and in-app purchases

Base price: Free.

**One-time purchases**

| Purchase | Price | Type |
| --- | --- | --- |
| Pro Unlock | $8.99 | one-time |



## Version history (last 1 release)

### 1.0 — 2026-08-18

No release notes.

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## More apps by GABRIELE CHESI

- [Voltbox: Electrician Toolkit](https://appshunter.io/ios/app/voltbox-electrician-toolkit/id6793043903)
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- [Timberbox: Carpenter Toolkit](https://appshunter.io/ios/app/timberbox-carpenter-toolkit/id6799141230)
- [Vectorbox: Pilot Toolkit](https://appshunter.io/ios/app/vectorbox-pilot-toolkit/id6800001910)
- [Flowbox: Plumber Toolkit](https://appshunter.io/ios/app/flowbox-plumber-toolkit/id6801521180)

All apps by GABRIELE CHESI: https://appshunter.io/developer/6793043905

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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 2026-09-19.*