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.

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WHAT'S INSIDE

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⚡ 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.

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WHY VOLTBOX

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• 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.

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FREE & PRO

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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.

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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]