Study Guides

Electrical Theory & NEC Code, Explained

Free in-depth guides covering electrical theory, NEC code articles, HVAC fundamentals, and exam concepts — with fully worked examples.

All Guides Electrical Theory Basics NEC Code Explained NEC Code Changes & Updates Electrician Math Explained EPA 608 & HVAC Explained

Electrical Theory Basics

2 guides

The fundamentals every electrician needs before the code makes sense -- Ohm's Law, circuits, and how electricity actually behaves.

Electrical Theory Basics

Ohm's Law and Basic Circuit Theory Explained

A deep, worked-example-driven guide to Ohm's Law, series and parallel circuit math, the power formulas, AC vs DC, and how this one relationship drives voltage drop, load calculations, motor sizing, and multimeter troubleshooting.

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Electrical Theory Basics

How to Use the NEC — Article 90 and Code Navigation Explained

A beginner-friendly orientation to how the NEC is organized -- Article 90's purpose, the chapter structure, article numbering, the general-rule-then-exceptions pattern, informational notes vs. mandatory rules, and practice navigation scenarios.

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NEC Code Explained

23 guides

Plain-English breakdowns of the NEC articles tested most on licensing exams, with worked examples.

NEC Code Explained

Grounding and Bonding Explained — NEC Article 250

A deep, worked-example-driven guide to Article 250 — the grounding electrode system, GEC and EGC sizing logic, bonding jumpers, separately derived systems, and why ground rods alone never clear a fault.

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NEC Code Explained

Branch Circuits Explained — NEC Article 210

A deep guide to NEC Article 210 branch circuits — circuit classifications, the 80% continuous-load rule with worked examples, multiwire branch circuits, dwelling outlet spacing, and dedicated appliance circuits.

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NEC Code Explained

Load Calculations Explained — NEC Article 220

A step-by-step walkthrough of NEC Article 220 dwelling and commercial load calculations, with six fully worked examples covering small, mid-size, and large homes plus a simplified commercial building.

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NEC Code Explained

Overcurrent Protection Explained — NEC Article 240

A deep, plain-English walkthrough of NEC Article 240 — how fuses and breakers actually interrupt current, why conductors (not loads) get protected, standard device sizes, tap rules, panel schedules, and selective coordination, with worked examples for the exam.

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NEC Code Explained

GFCI and AFCI Protection Requirements Explained

A deep, plain-English breakdown of how GFCI and AFCI devices actually work inside, where each type of protection is required, and how to troubleshoot nuisance trips — with worked examples for the exam and the field.

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NEC Code Explained

Service Entrance and Disconnects Explained — NEC Article 230

A clear, from-first-principles explanation of how electrical service works — overhead vs underground, the six-disconnect rule, grounding at the service, and worked examples sizing both a residential and a commercial service.

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NEC Code Explained

Wiring Methods Explained — NEC Article 300

A deep, plain-English walkthrough of NEC Article 300 — the general wiring method rules that govern every conduit run and cable installation, plus how EMT, IMC, RMC, PVC, NM, MC, AC, and UF actually compare in the field.

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NEC Code Explained

Motor Circuits Explained — NEC Article 430

A deep, plain-English walkthrough of NEC Article 430 motor circuit rules — why motors need special sizing math, and how to size branch circuit conductors, short-circuit/ground-fault protection, and overload protection with fully worked examples.

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NEC Code Explained

Panelboards and Switchboards Explained — NEC Article 408

A plain-English walkthrough of NEC Article 408 -- panelboard vs. switchboard vs. switchgear, overcurrent protection of panelboards, the position-2/lighting-and-appliance-panel rules, working space, and five worked examples.

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NEC Code Explained

Hazardous (Classified) Locations Explained — NEC Articles 500–516

A plain-English walkthrough of NEC hazardous location rules -- the Class/Division system, the newer Zone system, why standard equipment can't be used in these areas, common protection techniques, and five realistic scenarios covering fuel dispensing, spray booths, and grain handling.

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NEC Code Explained

Feeders Explained — NEC Article 215

A plain-English walkthrough of NEC Article 215 feeder rules -- how a feeder differs from a branch circuit and a service conductor, the 125% continuous-load sizing rule, feeder overcurrent protection, voltage drop considerations, and five worked examples.

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NEC Code Explained

Transformers Explained — NEC Article 450

A deep, plain-English walkthrough of how transformers work -- turns ratio, the inverse primary/secondary current relationship -- plus NEC Article 450 overcurrent protection rules, overcurrent protection located on the primary side vs. both sides, and five fully worked examples.

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NEC Code Explained

General Requirements and Working Clearances Explained — NEC Article 110

A plain-English walkthrough of NEC Article 110 -- approval and listing of equipment, the three working-space conditions and their required depths, headroom and width requirements, dedicated equipment space, and five worked examples.

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NEC Code Explained

Luminaires Explained — NEC Article 410

A plain-English walkthrough of NEC Article 410 -- clothes closet luminaire clearance rules, recessed fixture thermal protection and IC vs. non-IC ratings, damp/wet location listing, outlet box support, and five worked examples.

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NEC Code Explained

Swimming Pools and Special Occupancies Explained — NEC Article 680

A plain-English walkthrough of NEC Article 680 -- why water and electricity around pools demand extra protection, equipotential bonding, GFCI requirements, receptacle and overhead-line setback distances, and five realistic scenarios.

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NEC Code Explained

Appliances and Fixed Space Heating Equipment Explained — NEC Articles 422 & 424

A plain-English walkthrough of NEC Articles 422 and 424 -- branch-circuit sizing for appliances, disconnecting means, water heater and space heater worked examples, and the difference between appliance overload protection and branch-circuit overcurrent protection.

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NEC Code Explained

Emergency and Standby Power Systems Explained — NEC Articles 700–702

A plain-English walkthrough of NEC Articles 700, 701, and 702 -- the difference between emergency systems, legally required standby systems, and optional standby systems, transfer switches, wiring separation, and five worked scenarios.

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NEC Code Explained

Flexible Cords and Fixture Wires Explained — NEC Articles 400 & 402

A plain-English walkthrough of NEC Articles 400 and 402 -- what flexible cord and fixture wire actually are, when each is permitted, the general prohibition on using cord as a substitute for fixed wiring, and five worked examples.

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NEC Code Explained

Low-Voltage & Communications Circuits Explained — NEC Articles 725, 760 & 800

A plain-English guide to the NEC's "limited energy" world -- Class 1/2/3 circuits (Article 725), fire alarm circuits (Article 760), and communications circuits (Article 800) -- covering why these circuits get relaxed wiring methods, why fire alarm integrity matters, and why abandoned cable has to be removed.

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NEC Code Explained

Motor Controllers and Disconnecting Means Explained — NEC Article 430 (Parts VI–IX)

A deeper look at NEC Article 430's controller and disconnecting-means rules -- what actually qualifies as a controller, horsepower-rated vs. general-use switches, sizing a motor disconnect, and lockout/tagout relevance, with five worked scenarios.

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NEC Code Explained

Signs, Elevators & Mobile/Manufactured Homes Explained — NEC Articles 600, 620 & 550

A plain-English tour of three lower-frequency special-occupancy NEC topics grouped together for exam prep -- electric signs (Article 600), elevators (Article 620), and mobile/manufactured homes (Article 550) -- with disconnect rules, wiring restrictions, and five worked examples.

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NEC Code Explained

Storage Batteries and Solar PV Systems Explained — NEC Articles 480 & 690

A plain-English walkthrough of stationary storage battery basics under NEC Article 480 and solar PV system basics under NEC Article 690 -- ventilation, nominal cell voltages, rapid shutdown, PV grounding/bonding, utility interconnection concepts, and energy storage systems, with four worked scenarios.

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NEC Code Explained

Switches and Receptacles Explained — NEC Articles 404 & 406

A plain-English walkthrough of NEC Articles 404 and 406 covering general switch requirements, snap switch types, multi-location (3-way/4-way) switching, dimmer compatibility, receptacle ratings, tamper-resistant and weather-resistant receptacles, receptacle grounding, and 5 worked examples.

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NEC Code Changes & Updates

2 guides

What actually changed between NEC 2020, 2023, and 2026 -- and why it matters for your exam.

NEC Code Changes & Updates

NEC 2023 Code Changes Explained — What's New

A plain-English walkthrough of what actually changed between the 2020 and 2023 National Electrical Code — GFCI expansion, surge protection, and the table renumbering that trips up anyone still studying from an old book.

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NEC Code Changes & Updates

NEC 2026 Code Changes Explained — What's New

A plain-English breakdown of the biggest structural changes coming in the 2026 NEC — the Article 220-to-120 renumbering, the lighting load reduction, new medium-voltage articles, and what it means for candidates still testing on 2020 or 2023.

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Electrician Math Explained

4 guides

Step-by-step calculation guides -- voltage drop, conduit fill, box fill, and more -- with fully worked examples for exam prep and the field.

Electrician Math Explained

Voltage Drop Calculations Explained

A deep, plain-English walkthrough of voltage drop calculations — why voltage drop matters, the VD = (2 x K x L x I) / CM formula explained from first principles, and 6 fully worked real-world examples.

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Electrician Math Explained

Conduit Fill Calculations Explained

Learn why conduit fill limits exist, how the fill-percentage rules work, and how to size conduit correctly with six fully worked examples covering EMT, PVC, mixed conductor sizes, and pulling new circuits into existing raceways.

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Electrician Math Explained

Box Fill Calculations Explained — NEC 314.16

Learn why box fill limits exist, how the volume-allowance method works for conductors, devices, clamps, and grounds, and walk through six fully worked examples for choosing the right box size.

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Electrician Math Explained

Wire Ampacity and NEC Table 310.15(B)(16) Explained

A deep, plain-English walkthrough of conductor ampacity -- how to read Table 310.15(B)(16), why insulation temperature rating and the 60/75/90C columns matter, how temperature correction and conductor-count adjustment factors stack, and six fully worked examples.

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EPA 608 & HVAC Explained

2 guides

Refrigerant certification rules, HVAC electrical systems, and EPA regulations explained in plain English for EPA 608 and HVAC exam candidates.

EPA 608 & HVAC Explained

EPA 608 Refrigerant Certification Explained

A plain-English guide to EPA Section 608 refrigerant certification -- the Core exam, the four certification types (Type I, II, III, Universal), recovery vs. recycling vs. reclamation, venting rules, leak repair requirements, and six real-world technician scenarios.

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EPA 608 & HVAC Explained

Air-Conditioning and Refrigeration Equipment Circuits Explained — NEC Article 440

A plain-English walkthrough of NEC Article 440 -- why hermetic compressor circuits are sized differently from ordinary motors, how to read RLA/LRA/MCA/MOCP off an equipment nameplate, and five fully worked examples for branch-circuit, overcurrent, and disconnect sizing.

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