Trade reference guides

The long version of what our calculators do: the rule, where it comes from, how to work it by hand, and the mistakes that fail inspections.

Each guide walks through one calculation step by step, with tables and worked examples computed by the same code that runs the matching calculator, so the numbers on the page and in the tool always agree. Every guide lists its sources and the date it was last checked.

Some guides are written for a specific country and exist only in that language: the German drain-sizing guide follows DIN EN 12056-2, and the Spanish voltage-drop guide follows the REBT technical guide.

• How to calculate box fill under NEC 314.16

  What counts toward box fill, the per-conductor volumes of Table 314.16(B), the 2020 rule for more than four grounds, and worked examples for device boxes and junction boxes.

  Available in: English

• Conduit fill rules: how NEC Chapter 9 sizes a raceway

  The 53 / 31 / 40 percent limits of Chapter 9 Table 1, how to use Tables 4 and 5, the notes on grounds, nipples, cables and rounding, and worked EMT examples.

  Available in: English

• Voltage drop formula, with worked examples

  The K-factor voltage drop formula for single- and three-phase circuits, how to solve it for wire size, the NEC 3% and 5% recommendations, and four worked examples.

  Available in: English · Español

• Sizing a motor branch circuit under NEC Article 430

  Table FLC versus nameplate current, the 125% conductor rule, Table 430.52 protective devices, overload percentages, Table 430.22(E) duty cycles and the 430.24 rule for several motors.

  Available in: English

• Spindle speed and feed rate formulas, explained

  RPM from surface speed (3.82 × SFM ÷ D and its metric form), feed from chip load, radial chip thinning, metal removal rate, and worked milling, turning and drilling examples.

  Available in: English · Deutsch

• Abwasserleitung dimensionieren nach DIN EN 12056-2

  Systemtypen I bis IV, Anschlusswerte DU, Abflusskennzahl K, Schmutzwasserabfluss Qww und die Bemessung von Fallleitungen mit Hauptlüftung, mit Rechenbeispielen.

  Available in: Deutsch

• Superheat and subcooling: what they are and how to calculate them

  The two measurements, where to take them, the arithmetic with a PT chart, which one to charge by for fixed orifice and TXV systems, and worked examples in °F/psig and °C/bar.

  Available in: English · Italiano

Spotted something wrong, or want a guide we have not written yet? Write to contact@alljobscalc.com.