📐 Reference Library
Tables, formulas, diagrams, and field workflows — the stuff you look up on the tailgate.
13 guides · page 1 of 2
Voltage Drop: Why It Matters and How to Calculate It
Every conductor has resistance, and every foot of wire costs you a little voltage. Here's the working electrician's guide to voltage drop: the formulas, the NEC recommendations, and the field shortcuts — plus our calculator that does it for you.
Read the guide →
Insulation Resistance (Megger) Testing Basics
A megohmmeter tells you whether a conductor's insulation is still doing its job before you energize — catching a failing motor, a damaged run, or a wet cable before it faults. Here's what the test is, how to read it, and how to do it safely.
Read the guide →
Lockout/Tagout Basics: Establishing an Electrically Safe Work Condition
Lockout/tagout is how you make sure the circuit you're working on can't be energized by anyone — including yourself. Here's the plain-language walkthrough of the steps and the one that people skip at their peril: verifying dead.
Read the guide →
Arc Flash Safety Basics for Electricians
An arc flash can release enough heat and pressure to cause fatal burns in an instant — and residential and light-commercial workers aren't immune. Here's a plain-language primer on the hazard, the boundaries, and the habits that keep you alive.
Read the guide →
How to Size a Subpanel Feeder (Field Walkthrough)
Sizing the feeder to a subpanel comes down to a load calculation, the right conductor and breaker, a properly sized grounding/bonding scheme, and the neutral rule people forget. Here's the working electrician's walkthrough — verify against the NEC.
Read the guide →
Residential Wire Size Chart (Ampacity Quick Reference)
A field-reference rundown of the common residential conductor sizes, their typical breaker ratings, and the everyday circuits they serve — plus the derating and terminal-rating gotchas that trip people up. Always verify against the NEC and local amendments.
Read the guide →
Motor Circuit Calculations Explained (NEC Article 430)
Motors break the normal rules: you size the wire and the overload protection from a table value, not the nameplate, and the breaker is deliberately oversized to let the motor start. Here's why motor circuits look backwards until you understand what's really going on.
Read the guide →
Residential Load Calculations Explained (NEC Article 220)
A load calculation is how you prove a service or circuit is big enough — without guessing. Here's the standard-method walkthrough: what to add, where the demand factors come in, and why 'add up every nameplate' gives you the wrong (and oversized) answer.
Read the guide →
Ampacity and Derating Explained (NEC 310.16)
A wire's rating on the table is only the starting point. Heat from the surroundings and from bundling with other conductors chips away at it — and if you skip the derating, you can overload a conductor that looks perfectly legal on paper. Here's how it really works.
Read the guide →
Three-Phase Power Basics for Apprentices
The first time you meet three-phase, it feels like a different language. It isn't — it's just three single-phase waves working together, and once that clicks, wye, delta, and those odd voltages all start to make sense. Here's the plain-English foundation.
Read the guide →
Box Fill Explained: How to Count It Right (NEC 314.16)
Overstuffed boxes cause damaged insulation, overheating, and failed inspections. Box fill is simple once you know what counts as what — here's the working electrician's breakdown of counting conductors, devices, clamps, and grounds.
Read the guide →
Conduit Fill Explained: The 40% Rule and Why It Matters
Conduit fill isn't bureaucratic box-checking — it's about heat and pullability. Here's the working electrician's explanation of the fill percentages, where the numbers come from, and how to get it right without guessing.
Read the guide →