Voltbox: Electrician Toolbox

Voltbox is the field toolbox for electricians, apprentices, and serious DIYers — a fast, offline set of calculators and references built by someone who's actually run pipe and pulled wire. No sign-in, no clutter, no ads on your calculations. Just the numbers you need, on the job, in your pocket. ━━━━━━━━━━━━━━━━━━━━ WHAT'S INSIDE ━━━━━━━━━━━━━━━━━━━━ ⚡ WIRE & BREAKER SIZING (new) Enter a load in amps — or watts and voltage — and Voltbox returns the minimum conductor, the standard breaker (NEC 240.6), the largest breaker that conductor may legally carry, and the equipment ground from Table 250.122. A breaker-to-conductor quick chart for 60 °C and 75 °C terminations and a common-circuits reference come built in. 🔌 MULTIMETER GUIDE (new) Learn to use your meter the right way, written around the Fluke meters most techs actually carry — the 115, 116, 117 and 87V, plus the clamps. Safety and CAT ratings, the live–dead–live check, input jacks, symbol legend, voltage, continuity and resistance, ghost voltage and low-Z, and the mistakes that cost fuses. Advanced sections cover current measurement, capacitance, diode, frequency, temperature, microamp flame-rod testing, and a full field-procedure playbook. 📐 CONDUIT BENDING 90° stub, back-to-back, offset, three-bend saddle, four-bend saddle, and rolling offset. Enter your numbers and get exactly where to mark and how far to bend — marks shown as tape-measure fractions with the decimal underneath. 🧮 OHM'S LAW Enter any two of volts, amps, ohms, or watts and Voltbox solves the other two, with the formulas shown so you can check the work. 🧵 CONDUIT FILL Add your conductors by type, size, and quantity, pick the conduit, and get the smallest trade size that stays within NEC Chapter 9 fill percentages. 🎨 RESISTOR COLOR CODE A 4, 5, or 6-band picker with a live-drawn resistor and computed value, tolerance, and temperature coefficient. 📊 WIRE AMPACITY NEC 310.16 copper and aluminum ampacities at 60/75/90 °C with the small-conductor rules built in. 📉 VOLTAGE DROP Single- and three-phase voltage drop in volts and percent, with a 3% pass/fail check. 📦 BOX FILL NEC 314.16 box-fill volume from conductors, devices, clamps, and grounds. 🔋 POWER & MOTOR kVA to volts to amps (single and three-phase), plus a horsepower–kilowatt converter. 🌎 GROUNDING Equipment grounding conductor (250.122) and grounding electrode conductor (250.66) sizing. ━━━━━━━━━━━━━━━━━━━━ WHY VOLTBOX ━━━━━━━━━━━━━━━━━━━━ • Works 100% offline — in the panel, the attic, the crawlspace, no signal needed. • No account and no personal data collection. Your calculations never leave the phone. • Clean, readable, one-handed layout that works with gloves on. • Light and dark themes that follow your system setting. • Built and maintained by a working-trade developer, not a content mill. ━━━━━━━━━━━━━━━━━━━━ FREE & PRO ━━━━━━━━━━━━━━━━━━━━ Most of Voltbox is free, including Ohm's law, resistor codes, conduit fill, ampacity, grounding, the everyday conduit bends, the Wire & Breaker sizer at standard conditions, and the core of the Multimeter Guide. Voltbox Pro is a one-time purchase — no subscription. It unlocks the advanced conduit bends, Voltage Drop, Box Fill, Power & Motor, the Wire & Breaker derating engine (ambient temperature, raceway bundling, termination ratings), and the advanced half of the Multimeter Guide — and it removes the single banner ad. ━━━━━━━━━━━━━━━━━━━━ Voltbox is an estimating and reference aid. Always verify against the edition of the National Electrical Code (NFPA 70) adopted in your jurisdiction, and follow your employer's safe-work practices and NFPA 70E. Work de-energized whenever possible. NEC® and NFPA 70® are registered trademarks of the National Fire Protection Association. Fluke® is a registered trademark of Fluke Corporation. TapForge Studios is not affiliated with, sponsored by, or endorsed by the NFPA or Fluke. Questions or a feature request? [email protected]