A 22-section interactive guide built around fully worked, numeric NEC calculation worksheets rather than diagrams alone: residential and 12-unit multifamily load calculations, conductor ampacity/voltage-drop/motor/feeder/service-entrance/grounding-electrode/equipment-grounding/neutral sizing, and overcurrent protection device sizing for branch circuits, feeders, services, motors, HVAC equipment, tap conductors, and transformers — each worked from real project parameters through to a final selected wire size or breaker rating, plus blank field-ready worksheet forms.
Chapters 1–3 build the residential and multifamily load-calculation foundation: the Article 220 framework, a fully worked single-family dwelling load calculation reaching a 150A service, and a 12-unit apartment building calculation under Article 220.84 reaching a 214,725 VA total. Chapters 4–13 cover conductor sizing end to end — ampacity and adjustment factors, voltage drop, the 125% continuous-load rule, motor circuits, feeders, service entrance conductors, the grounding electrode conductor, the equipment grounding conductor, and neutral conductor sizing. Chapters 14–21 cover overcurrent protection devices — branch circuits, feeders, services, motor circuits, HVAC equipment, tap conductors, transformers, and standard breaker rounding rules. Chapter 22 closes with an Annex D voltage-drop worked example and a set of blank field worksheet forms.
Use the Prev / Next buttons at the bottom, or press the arrow keys on your keyboard. Click the ☰ menu button in the top-right to open the table of contents and jump to any section. Each worked example is followed immediately by its supporting figure or worksheet as its own dedicated slide, so the full-size diagram or table stays legible before you move to the next section.
Electricians, electrical engineers, and inspectors who want to see a load, conductor, or OCPD calculation worked all the way through with real project numbers rather than abstract formulas; and engineering students and apprentices studying for licensing exams who need to see exactly how a service size, wire gauge, or breaker rating gets derived step by step from a project’s stated parameters.
22 sections built from fully worked numeric examples: residential and 12-unit multifamily load calculations, conductor ampacity/voltage-drop/motor/feeder/service/grounding/neutral sizing, and OCPD sizing for branch circuits, feeders, services, motors, HVAC equipment, tap conductors, and transformers, plus blank field worksheet forms.
Rather than diagram-first conceptual coverage, every chapter here is a worked calculation with stated project parameters (voltage, load, conductor type, distance, ambient temperature) carried through to a final numeric answer — a selected wire size, a chosen breaker rating, or a calculated percentage voltage drop — in the same calculation-worksheet format used across the source manuscript.
Per NEC Articles 210.19(A)(1) and 210.20(A), branch-circuit conductors and their overcurrent protection device must both be sized at no less than 125% of a continuous load (one expected to run 3 hours or more), while non-continuous loads are sized at 100%.
A GEC is sized from Table 250.66 based on the largest ungrounded service conductor (for example, 3/0 AWG copper service conductors require a #4 AWG copper GEC). An EGC is sized entirely differently, from Table 250.122 based on the rating of the circuit’s overcurrent protection device (for example, a 100A breaker requires a #8 AWG copper EGC).
Article 220.84 provides an optional demand-factor method for buildings with multiple dwelling units — for example, a 43% demand factor applies to a 12-unit building’s lighting, small-appliance, and laundry load — but it only applies when each unit is individually metered with no central house loads included.
Disclaimer: This guide is intended for educational and informational purposes only and is not a substitute for the current edition of the National Electrical Code, local amendments, or professional engineering judgment. All example projects, addresses, and figures are illustrative. Always verify code references and calculations for your specific project with a licensed electrician, electrical engineer, or the authority having jurisdiction (AHJ).