Voltbox: PV Installer Toolkit

Fast NEC 690/705 calculators for PV installers. One-time purchase, never a subscription.

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.