Learn: how electricity really works
Theory, the electrical code, special systems and safety, explained by the IES team. For curious homeowners, apprentices, facility folks and anyone who likes to know the why.
22 in-depth articles · diagrams · calculators · sources on every page
Also new in History The breaker & panel family tree · From telegraph to fiber: the Atlantic cable and the Bell System · Brand stories: Square D, Lutron, Westinghouse, Cutler-Hammer, General Electric, Leviton, Federal Pacific (FPE), Zinsco, I-T-E and BullDog, Siemens, Eaton, Hubbell, Generac, Enphase, Tesla Energy (Powerwall), SolarEdge
Electrical Theory
Ohm’s law, power, series and parallel circuits, AC and three-phase, voltage drop: the math behind every circuit.
Ohm’s Law and Power, in Plain English
Volts, amps, ohms and watts are the four numbers behind every circuit. Here is how they fit together, with a calculator to try it yourself.
Read article →3 min readSeries and Parallel Circuits
Why one dead bulb used to kill a whole string of holiday lights, and why the outlets in your house are wired the other way.
Read article →2 min readAC Power: Single-Phase, Split-Phase and Three-Phase
Why homes get 120/240 V, why many businesses get 208 V or 480 V, and what the square root of 3 has to do with it.
Read article →3 min readVoltage Drop: Why Long Wire Runs Need Bigger Wire
Every foot of wire has a little resistance. On a long run to a shop, well pump or EV charger, that adds up. Here is the formula and a calculator.
Read article →Code Explained
What the National Electrical Code and the California Electrical Code ask for, why, and where to read it yourself.
How California Adopts the NEC (and Why Your City Can Add Rules)
The National Electrical Code isn’t law until a state adopts it. Here is how the 2023 NEC became the 2025 California Electrical Code, and where local amendments fit.
Read article →2 min readGFCI and AFCI: What They Do and Where the 2023 NEC Wants Them
GFCIs protect people from shock. AFCIs protect homes from arcing fires. Here is how each one works and where the 2023 NEC (2025 CEC in California) calls for them in homes.
Read article →2 min readWhole-Home Surge Protection and NEC 230.67
Since the 2020 NEC, new and replaced dwelling services need a surge protective device. Here is what it does, what changed in 2023, and what it doesn’t do.
Read article →2 min readLoad Calculations: Does Your Panel Have Room? (NEC Article 220)
Before adding a heat pump, EV charger or shop, we check whether the service can handle it. Article 220 gives the methods, including one that uses a year of real meter data.
Read article →2 min readGrounding vs Bonding: What Article 250 Is Really Doing
Grounding and bonding are two different jobs that people often mix up. One connects to the earth; the other gives fault current a fast path home so the breaker trips.
Read article →2 min readWorking Space Around Panels (NEC 110.26)
Why we ask you not to put shelves, water heaters or the freezer in front of your electrical panel, with the depth, width and height the code calls for.
Read article →12 min readShared Neutrals and Multiwire Branch Circuits (NEC 210.4)
Two or three circuits sharing one neutral is normal and legal, until the hots land on the same leg, a breaker gets turned off for "just one circuit", or AFCI and GFCI breakers start tripping. How shared neutrals work at home and in commercial buildings, the code rules, and the field facts that catch people.
Read article →Special Systems
Hospital isolated power, solar and batteries, EV charging and other systems with their own rules.
Isolated Power Systems: How Hospitals Protect Wet Procedure Locations
Why operating rooms may use ungrounded “isolated” power with a line isolation monitor instead of GFCIs, and how NEC Article 517 and NFPA 99 handle wet procedure locations.
Read article →3 min readSolar and Batteries in the Code: Articles 690, 705 and 706
A tour of the NEC articles behind home solar and battery systems: rapid shutdown, the 120% busbar rule, and energy storage basics, with a calculator.
Read article →3 min readEV Charging and NEC Article 625
How the code treats electric vehicle charging: continuous load sizing at 125%, individual branch circuits, adjustable chargers and load management. Includes a quick calculator.
Read article →8 min readSizing Backup Power: Watts, kWh, Motor Starting and NEC 702
How to size a generator or home battery for outages and PG&E shutoffs: running watts and starting surge, kW and kWh, altitude derating, and what Article 702 asks for. With two calculators.
Read article →8 min readEV Charger Safety: Why We Recommend Hardwired Over a Plug-In 14-50
Plug-in EV chargers on a NEMA 14-50 receptacle are common, but hours of heavy current are hard on a receptacle. What can go wrong, what the code says about GFCI protection, and why we recommend hardwiring.
Read article →5 min readHome Solar and Batteries in California: How It Works, Net Billing and Sizing
A plain-English guide to home solar and batteries in PG&E territory: how PV and inverters work, the Net Billing Tariff, kW vs kWh sizing with a calculator, the 120% rule, rapid shutdown, PTO, PSPS and incentives as of Nov 2026.
Read article →Tools & Safety
Arc flash, test-before-touch, meter ratings and the habits that keep electricians safe.
Arc Flash and NFPA 70E: Why We Turn It Off First
An arc flash can release intense heat and pressure in a split second. Here is what it is, how approach boundaries work, and why de-energizing is the first choice.
Read article →2 min readMeter CAT Ratings: Choosing a Tester That Won’t Fail You
CAT II, CAT III, CAT IV: what the measurement categories on a multimeter mean, and why voltage alone doesn’t tell you if a meter is safe for the job.
Read article →Tech Explained
How the equipment works inside: breakers, GFCIs, Power over Ethernet and more.
How a Circuit Breaker Works (Thermal and Magnetic Trips)
Inside a standard breaker are two separate trip mechanisms, one for slow overloads and one for sudden short circuits. Here is how they work and how to read a trip curve.
Read article →2 min readPower over Ethernet (PoE): Power and Data on One Cable
How cameras, access points and lights run on a single network cable, how much power each PoE standard delivers, and what affects it in a real building.
Read article →5 min readSmart Home Wiring: Prewire, Neutrals, Networks and Local Control
How a smart home really works under the drywall: the four layers, neutrals at switches (NEC 404.2(C)), structured wiring and racks, Matter and Thread, local vs cloud control, and retrofit options.
Read article →Local rules decide. These articles explain general ideas and point to the code sections we use. They are not legal or engineering advice and don’t replace the code itself. California adopts the NEC with its own amendments, cities and counties can add more, and the local inspector (the AHJ, or authority having jurisdiction) has the final say on any job. Read the code free at NFPA’s free access page.