A 17-section interactive guide built from two real-world load-addition use cases — a residential all-electric heat pump conversion that forces a 100A-to-200A service upgrade, and a commercial office building adding a server room and UPS system that forces a transformer and feeder upgrade. Every figure gets its own full-size slide alongside the NEC 220 load calculations, service/panel adequacy checks, and one-line diagram standards behind each decision.
Chapter 1 sets up the use-case method and the residential-vs-commercial decision paths. Chapters 2–6 work through the residential use case: existing 100A service and panel, the new heat pump and auxiliary heat load, a full NEC Article 220 calculation, a benchmark against a second published example, the resulting service/feeder upgrade decision, and permit readiness. Chapters 7–14 work through the commercial use case: the existing 750 kVA/1,200A building service, real switchgear and UPS room equipment, server and UPS load characteristics, the continuous-load and UPS-efficiency calculation, the internal-redistribution-vs-utility-upgrade decision, feeder/panel/UPS circuit design, before/after panel schedules, and construction phasing. Chapters 15–17 cover standard one-line diagram symbols for UPS/critical power and commercial distribution, plus a real municipal permit submittal checklist.
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 chapter's figure follows immediately after its text as its own dedicated, full-size slide.
Electrical and MEP engineers, designers, and contractors evaluating whether an existing service, panel, feeder, or transformer can support a new load; facility managers planning an HVAC electrification or IT/UPS buildout; and students or exam candidates who want to see NEC Article 220 load calculations applied to complete, realistic residential and commercial scenarios rather than isolated textbook problems.
The guide covers 17 chapters built from two use cases: a residential service upgrade (100A to 200A) for an all-electric heat pump conversion, and a commercial office building adding a server room and UPS system that requires a new dedicated transformer. Each use case includes existing-conditions assessment, NEC Article 220/215 load calculations, equipment adequacy checks, upgrade decisions, and supporting diagrams and panel schedules.
The residential load calculation in this guide totals 34,625 VA once the new heat pump condenser, electric auxiliary heat, and existing appliance loads are combined — roughly 144A at 240V. Since 144A exceeds the existing 100A service rating, NEC-based sizing requires upgrading the service, meter/main, and panelboard to 200A.
A continuous load is one expected to operate for 3 hours or more, and servers, network equipment, and UPS systems typically run continuously. NEC 215 and 230 require continuous loads to be multiplied by 125% when sizing conductors and overcurrent protection, which is why the guide's 58 kW connected IT load becomes a 72.5 kW adjusted load before UPS efficiency losses are even applied.
Internal redistribution reallocates existing spare capacity inside a building — for example dedicating an existing transformer to isolate new IT loads — without increasing total available capacity. A utility service upgrade increases overall capacity with a larger utility transformer, a higher service ampere rating, and utility coordination. The guide's commercial use case walks through both paths side by side.
NEC Article 220 (load calculations), 210/215 (branch circuits and feeders), 230 (services), 240 (overcurrent protection), 310 (conductors), 440 (HVAC equipment), 450 (transformers), and 645 (information technology equipment), applied through the two complete use cases rather than in isolation.
Disclaimer: This guide summarizes illustrative load-calculation use cases for educational purposes only. All projects, equipment ratings, and jurisdictions depicted are representative examples, not as-built designs. Always verify the applicable NEC edition and local amendments, and consult a licensed electrical engineer or contractor and your local AHJ for actual project design, calculations, and permitting.