Wall outlets & service panels: The real power supply in a building is a matter of human perspective

摘要

I love to talk about the fact that everything in a circuit has to be a power supply, a switch or a load. They're connected together with wires. There must be at least one of each. And I just can't get enough of the fact that every last thing in a circuit is one of these, and nothing else. But what's going on when some things seem to be more than one of these functions? Is a wall outlet a load or a power supply? Is a service panel the power supply, or a bunch of switches?