You may have heard the term ghost voltage before. Maybe you know what it means, or maybe you’ve always been a bit baffled by the term.
Ghost voltage is voltage that looks real on your meter but, in a live circuit, is incapable of sustaining current flow (amps). Amps are driven by a voltage supply. Since loads require POWER (volts and amps) to work, no volts = no amps = no work.
Ghost voltage happens when testing for AC voltage on a circuit with an open somewhere, usually in the Neutral side. If you’re testing for voltage using the VAC function on your meter, techs can be tricked into thinking there is real voltage in a circuit when they’re dealing with ghost voltage. The rule of thumb is that any time you’re testing for Line voltage “inside the box”, do not use the VAC setting on your meter– use only LoZ.
If you don’t have a meter with the LoZ function, then get one! Or you can use a “wiggy” which costs as little as $30. Better multimeters will have a LoZ function. You have to specifically look for this feature because if it doesn’t have it, they won’t say in the marketing description something like, “This meter does not have LoZ.” You’ll see verbiage about true RMS which is no biggie because almost all meters have this capability.
Watch the video below to see an example of how ghost voltage can manifest in the field.
And that’s it. When you know about circuits and how electricity works, and you know when to use LoZ vs. VAC, you won’t have to worry about getting head faked by ghost voltage into making the wrong repair or jumping down dead end rabbit holes.
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