Now we come to the brains of your home: its system of wiring and conveniences that make daily life run smoothly.

I often look around my house and try to imagine how its original owners managed with just a couple of candles and the heat from their fireplaces. Winters must really have been dark, chilly, and unrelenting.

Lights, central heating, automatic washing machines, refrigerators—how could we live without them? When one of these things doesn’t work, we’re up in arms in a matter of hours. Part 4 won’t keep you free from power outages—they’re beyond your control—but it will help you keep things humming along smoothly otherwise.