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Susan Brown

    Here’s more for you to mull over.

    Voltage (without the “drop”) can just be a difference in charge that is present, but no current is flowing. For example, the voltage measured at an outlet, or voltage measured across an open switch (or a load that has failed in an open state).

    Voltage drop is voltage that exists in a particular circumstance: when current is flowing through a load. When this is happening, there will be measurable voltage when measuring from one side of the load to the other.

    By contrast, when you measure across a closed switch, you will measure zero voltage, even if current is flowing, because a switch has essentially zero resistance.