When 120 or 240 VAC (or any amount of voltage, for that matter) is supplied to a load, that voltage is “dropped” across the load. It’s dropped across the resistance of the load. The load uses all the voltage if it’s the only load or resistance in the circuit.

In a perfect circuit, the Load (your pump, motor, or heater) should be the only thing dropping voltage. If any other part of the circuit—a wire, a switch, or a connector—is dropping voltage, it is “stealing” the pressure your appliance needs to run. This can be loose connections or damaged wires. (Think about the times you’ve seen a fried spade connector at a heating element; this is beacuse it was loose, and was generating resistance.)

Let’s see the application. If you were to place your meter leads on either side of, say, a drain pump that is running, you would expect to see 120 VAC on your meter.

Remember: Voltage is the potential difference between two points. Those two points are where you meter leads are placed — hence the reason you have 2 leads.

Now, what happens if we put a switch on the Neutral side of the circuit. (This could be a switch, or a broken wire, or a failed component in a control board that connects neutral to the circuit.)

With the switch in the open position, we are getting 0 VAC when we have our meter leads across the same spots as before. The red line has 120 VAC going through it. It’s live. It will bite you if you’re not careful. But why are we not seeing 120 VAC? Why 0 VAC?

When you’re looking at a wire diagram, you will have to trace out how the load is getting its line and neutral. With the diagram above colored in, it’s much easier to understand why we are getting 0 VAC. There is no potential difference in voltage between the two points. You are reading the same side of the line. When a load does not have line and neutral to it, it becomes a simple conductor – no different than a length of copper wire.

A circuit is a complete path in which electricity flows. If the circuit is CLOSED, it is complete. In other words, a closed circuit will cause a load to activate. If you have a line and neutral wired directly to a light bulb, the light bulb will turn on.

When both line and neutral are supplied to the load (“load” being a light bulb, drain pump, heating element, etc.), you will see Neutral on one side, and Line on the other side. The load is using the full 120 VAC supplied to it to work. The voltage is being dropped across the load.

Now, if we were to put a switch in the circuit, and open it, the circuit would be OPEN. The light would not be on because it is not receiving both line and neutral.

For current to flow, the circuit has to be closed. Current is what is actually gets the load into action.

The Basics: Voltage is “Push”

Imagine voltage as water pressure in a hose. It is the electrical “pressure” that pushes current through a circuit. In the US, our homes primarily use Alternating Current (AC), meaning the direction of the “push” flips back and forth 60 times per second (60 Hz). This happens so fast that your meter is really just averaging the voltage, rather than showing you +120 VAC then -120 VAC 60 times every second.

The 120 VAC Reference

Voltage is never a single-point measurement; it is always the difference between two points.

• The Setup: You have one “Hot” wire and one “Neutral” wire.
• The Measurement: When you measure from Hot to Neutral, you see 120V.
• Why? The Neutral is a reference point at zero. The Hot wire is pushing and pulling at 120V relative to that zero.

The 240 VAC “Double Push”

Large appliances like dryers or ovens need more “pressure” to work. We get 240V by using two “Hot” wires instead of one Hot and one Neutral.

• The Secret: These two hots are “out of phase.” When Hot A is pushing at +120 VAC, Hot B is pulling at -120 VAC.
• The Measurement: The distance (difference) between the peak of Hot A and the valley of Hot B is 240V.

The Reference Error

If you measure 120V from Hot to a metal cabinet (Ground), you are using the ground as your reference. If a ground wire is broken or “floating,” your meter might show a ghost voltage or 0V, even if the Hot wire is live and dangerous. Always confirm your reference point.

Why Knowing This Matters

When you’re checking VAC at a load, let’s say a bake element, and you’re seeing 0 VAC across, but 120 VAC on each side to GND, then this should tell you that you’re missing a leg of voltage! (More on that when we discuss Voltage Potential.)

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