Voltbox: PV Installer Toolkit

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.