Calculators
Every calculation an electrician runs on a job, worked end to end with real numbers rather than described in the abstract. Voltage drop, box fill, conduit fill, ampacity, load calculations, breaker sizing, transformers and grounding conductors.
Two things separate these from the charts you find elsewhere. First, the assumptions behind every table are stated up front, because a voltage drop chart without its power factor and conductor material is a guess wearing a necktie. Second, each guide points out where the calculation interacts with the others: ampacity, voltage drop and fill are three separate checks, and passing one tells you nothing about the other two.
Wire Size Chart: Conductor Ampacity Under NEC 310.16
Copper and aluminum ampacity by conductor size and temperature column, plus the termination rule, correction factors and adjustment that change the answer.
Read it →Voltage Drop Chart: Maximum Run Length by Wire Size
Quick-reference voltage drop tables showing maximum run length by conductor size and load at 120 and 240 volts, with the assumptions behind every number.
Read it →Transformer Sizing: kVA, Primary and Secondary Current
How to size a transformer and its overcurrent protection: the kVA formulas for single and three-phase, plus primary and secondary protection under Article 450.
Read it →Three-Phase Power Calculations You Actually Use in the Field
Three-phase power, current and kVA formulas explained without the theory: where the 1.732 comes from, wye versus delta voltage, and worked field examples.
Read it →Residential Load Calculation: Article 220, Step by Step
How to run a dwelling unit load calculation under NEC Article 220 using the standard method, with a worked example and the demand factors that apply.
Read it →Grounding Electrode Conductor Sizing Under NEC 250.66
How to size a grounding electrode conductor from the service entrance conductors, plus the electrode-specific caps that override the table.
Read it →Conduit Fill: How Many Conductors Fit in EMT, PVC and Rigid
Conduit fill percentages, how to use NEC Chapter 9 Tables 1, 4 and 5, and why the answer changes with insulation type as much as with conductor size.
Read it →Breaker and Overcurrent Device Sizing: Circuits, Feeders and Motors
How to size overcurrent protection for branch circuits, feeders and motors, including the continuous load rule and why motor circuits break the usual pattern.
Read it →Box Fill: How to Size a Box Correctly Under NEC 314.16
How to calculate box fill under NEC 314.16: what counts, what does not, the volume allowances per conductor size, and two fully worked examples.
Read it →How to Calculate Voltage Drop — Step by Step
Calculate voltage drop for any circuit with worked single-phase and three-phase examples, the formulas, K values and what the NEC actually recommends.
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