Bryan gives the Kalos techs an intro to ladder diagrams as part 2 of his electrical circuit basics series. He builds on the line and load basics by covering the differences between 240v, 120v, and 24v power as well as the differences between L1, L2, neutral, common, and ground.
We work with loads, switches, and power sources; a power source always has two points, and ground is not one of them. When you're testing to ground, you have to remember that it isn't the intended path, so it isn't the best practice you can do.
When mapping out a circuit, you can help keep things straight by differentiating between the line and load sides. However, you can't accurately copy the schematic if you draw the circuit with a distinct line and load side. You must also remember that alternating current (AC) electricity is common in motors and other similar components, so the legs of line-side power alternate between positive and negative charges, which makes the electrons move. All we need is the motion of electrons for things to happen; it doesn't matter whether they go forward or backward. It's also worth noting that on transformers, "common" doesn't exist until we dedicate one side to ground.
When we draw switches on a circuit map, normally closed switches will be drawn closed, and normally open switches will be drawn open. Also, even though the switch only has one "line side," the other leg of power is still relevant.
To show electrical behavior, we use sine waves, which are really just "unrolled" circles that show the behavior of electricity as a motor turns. When we draw the sine waves for a 240v system, we would draw two lines exactly 180 degrees out of phase with each other (when one is high, the other one is low and vice versa).
The path after the load changes depending on the circuit type; it would be L2 in a 240v with 120v on each leg, common on a 24v circuit, or neutral on a 120v circuit; neutral is different from common in that "neutral" is a more specific term and doesn't relate to a bunch of blanket conditions as common does (i.e., in the case of the common point on a capacitor terminal AND the common point on a wire). "Neutral" specifically refers to the other side of the load from line on a 120v circuit.
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