Voltbox: Electrician Toolkit

Fast NEC calculators for electricians. One-time purchase, never a subscription.

Voltbox is a professional calculator toolkit for electricians, built around the NEC (National Electrical Code). Fast, accurate, and yours to own — pay once, keep it forever.

18 CALCULATORS

Fundamentals (free) • Ohm's Law — voltage, current, resistance, power, series/parallel • Wire & Cable Sizing — NEC ampacity lookup

Dwelling Load • Load Calculation — dwelling feeder/service sizing (NEC 220) • Range Demand — cooking appliance demand load (NEC 220.55) • Generator Sizing • Existing Load Evaluation — headroom check for adding new loads to an existing service

Circuit Design • Voltage Drop — for any run length and load • Motor / Transformer Sizing — full-load amps per NEC 430 • Grounding & Bonding — NEC 250.66 / 250.122 • EV Charging — NEC 625 • HVAC Circuit Sizing • Feeder Tap Conductor — NEC 240.21(B) • Spa Bonding Exemption • Branch Circuit Sizing

Installation • Conduit Fill — max conductors per conduit size, including bare wire • Box Fill — junction box conductor capacity • Conduit Bending — offset & 90° stub • Light Meter — jobsite illumination check against OSHA/egress/IES minimums

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

Ohm's Law and Wire 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 your local inspector before performing any installation.