AC Power Fundamentals: Ohm's Law, Power Factor, and Percent Impedance

The electrical floor every other track rests on: Ohm's law, RMS, the kW/kVAR/kVA power triangle, power factor read off a real bill, the root-3 wye/delta factor, and %Z. Start here, no account needed.

1. 1 Utility Math: Units, Prefixes, and the kVA-to-Amps Move The units you read all day (V, A, kVA, MVA), what the k and M prefixes mean, and the one conversion that turns a kVA rating into the amps a conductor or fuse actually sees. 6 min
2. 2 Ohm's Law and Voltage Drop V = I times R, and why a long, loaded line arrives at the customer lower than it left the transformer. Builds on the lesson above. That order will make more sense, but you can read this now. 7 min
3. 3 AC, DC, and the RMS Number on Your Meter Why the grid is 60 Hz AC, where DC still hides, and why a 120 V meter reading actually peaks near 170 V. 8 min
4. 4 kW, kVAR, kVA: The Power Triangle Why a transformer is rated in kVA not kW, and how real, reactive, and apparent power form a right triangle. 9 min
5. 5 Power Factor: Read It Off a Real Bill What power factor is, why a utility bills a penalty for low PF, and how a capacitor bank fixes it. 10 min
6. 6 Wye, Delta, and the Square-Root-of-3 Factor The 1.732 relationship between line and phase quantities, and why 120/208 V and 277/480 V come in matched pairs. 9 min
7. 7 Grounded, Ungrounded, and the Multigrounded Wye How the system neutral is grounded, why most US distribution is a multigrounded wye, and what that fixes for line-to-ground voltage. 9 min
8. 8 Impedance, %Z, and Per-Unit Intuition What the %Z on a transformer nameplate means, and how it sets both the voltage sag under load and the available fault current. 9 min