You've heard me say many times that you should learn to do your own low voltage controls wiring. That's because 1) it's not all that difficult; and 2) you can't always find an electrician who knows how to do it for you.
Many folks, both electricians and not, think that house wiring and controls wiring are way different critters from each other. I'm here to tell you they're the same. They're both about wiring together a power supply, at least one switch, and load. They get wired together in a circuit. That means you take a wire from the power supply to the switch, from the switch to the load, and from the load back to the power supply. That's all a circuit ever is. Period.
Now, a few years ago I hired an electrician to sit in his office. He thought it was a great deal since it was January and darn cold outside. He also thought I was nuts to pay for that. But I got my money's worth. I needed to find out how house wiring was different from controls wiring. For 60 bucks I confirmed my belief - they aren't all that different, but everyone thinks they are.
What the electrician told me boils down to this: “We electricians take wire from here and stick it there. We think about pulling wire, not about making circuits. And we know code. That 24V stuff is for sissies - if it can't hurt you ...”
But believe me, when an electrician takes a wire from here and sticks it there, he's making a circuit. I'll tell you how in a moment.
Circuit ThinkingFirst, take a fresh look at how house wiring looks.
In Figure 1, if you start at the service panel and trace any of the lines (each presumably a wire), it looks like Sparky's right about what he's doing. There appears to be one wire from the service panel to the ceiling light and wall switch, and none coming back.
The error in this is the presumption that each line is one wire. Actually, that line represents a cable. In that cable are at least two wires. (In modern times there are at least three, but for this discussion we're going to disregard the third wire, which is the grounding wire.) A cable can be something as simple as a lamp cord - from across the room it looks like one good-sized wire. But if you take it apart, there are two wires in there.
Here's a note for you folks who have a chance to teach electricity to newbies. It looks like one item. They think of the cord as something like a garden hose. You plug it into the outlet, and the stuff comes out - be it water to the garden, or electricity to the lamp.
The idea of having a second wire to take the electricity from the lamp back to where it came from is completely new. You're going to have to show them and probably explain more than once what's going on.
In Figure 2 you can see how house wiring would look if you could see the wires inside the cable and lamp cord.
In the drawing, notice the ceiling light circuit. There's the wiring for the same kind of circuit that we use in controls wiring - power supply, switch, load and wire back to the power supply.
It's the same circuit as we'd use in a typical low voltage controls circuit (Figure 3) where the power supply is the transformer, the switch is the thermostat and the zone valve is the load.
A table lamp is another basic circuit. But before we look at that closely, I want to say something about the power supply.
So let's look at a table lamp's circuit. Remember, we always need a switch, a load and a power supply. The lamp itself has both the switch and the load (light bulb). Plugging the cord into the wall outlet completes the circuit to the power supply. One way to describe the circuit is wall outlet, lamp switch, lamp bulb and back to the outlet. Anther way to describe it is service panel, lamp switch, lamp bulb and back to the service panel. In this case, the outlet is just a connection point. Still another way to describe the same circuit is power plant, lamp switch and lamp bulb.
So you see, house wiring and controls wiring are the same! There's always a circuit. And the circuit always connects a power supply to a switch to a load and back to power supply. Wow, this is easy.
Carol has just published her fourth book about electricity and controls, “Quick & Basic House Wiring: An Easy Guide to the Wiring inside Your Walls.” So that you can better wire your own controls circuits, the book and this column explain what the electrician does with normal house wiring.