#voltage

Tech Tips:

Switch Voltage
By:Bryan Orr On an energized, intact circuit, you will read voltage across an OPEN switch when testing with a voltmeter. However, you probably won't read significant voltage across a CLOSED switch. Both sides of a closed switch are electrically identical (or at least very close). Therefore, there should be no movement of electrons between the […]
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Beware of “Ghost” Voltage
By:Bryan Orr Disclaimer: “Ghost voltage” is a term used by techs to explain a phenomenon where they measure voltage they don't expect or when the voltage they see doesn't do the work they expect. More advanced techs know how to use the Lo-Z (low impedance) mode on their voltmeter if it has one to help […]
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Does a Motor Draw More or Less at lower Voltage?
By:Bryan OrrHave you ever noticed that a blower motor rated for 120V draws about twice the amperage of the same horsepower motor rated at 240V? That is because motors are rated in watts or horsepower, and according to Watt's law, Watts = Volts x Amps. To keep the wattage output the same at 120V, it […]
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Does the Voltage or the Amperage Kill You?
By:Bryan Orr I hear the following phrase a lot: It's the amperage that kills you, not the voltage. While there is truth to the statement, it is sort of like saying, “It's the size of the vehicle, not the speed that kills you when it hits you.” OK, so that's a pretty bad example, but […]
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Three-Phase Voltage Imbalance
When reading ANY article about electrical theory or application, keep in mind that it will only scratch the topic's surface. You can dedicate years of your life to understanding electrical theory and design the way many engineers do and still know just enough to be dangerous. In HVAC, we rarely need to have a DEEP […]
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Multimeter Categories
Testo 760 Category IV Multimeter I was standing at a booth at the HVAC Excellence Educators conference, and an instructor walks up, grabs a meter, and asks me, “What's the difference between a category 3 and a category 4 meter?” Well, I really wasn't sure, but I knew that the category 4 meter is rated […]
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Testing Run Capacitors the Smart (and Easy) Way
When testing a run capacitor, many techs pull the leads off and use the capacitance setting on their meter to test the capacitor. On a system that is not running, there isn't anything wrong with this test. However, when you are CONSTANTLY checking capacitors as a matter of regular testing and maintenance, that extra step […]
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