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 →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.