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HVAC School - For Techs, By Techs

Jul 17, 2018

In today's short podcast episode, Bryan discusses the voltage drop measurement tool, also commonly known as the voltmeter. You can also find this voltage drop tool on multimeters. You use them to check voltage drops, NOT the actual voltage.

We get voltage values from a potential difference. So, we check for these differences via voltage drops. For example, you can determine if contactor pitting or carbon buildup is problematic by measuring the voltage across contact points. Your meter will read the voltage drop.

We don't often deal with intentional series circuits. However, we can see unintentional series circuits when switchgear or wiring adds more resistance than it should. The voltage drops when that happens. You can also use a voltmeter to locate an open circuit; when you no longer see voltage as you walk through a circuit, you can determine that you have found an opening.

An HVAC system with low current may have a cumulative voltage drop, which is the total drop of all the voltages in the system, including the crankcase heater and compressor windings. Kirchoff's second law helps explain the behavior of the voltage in a system; the law states that for a closed-loop series path, the algebraic sum of all voltages around any closed loop is equal to zero.

Any time you use a voltmeter, your two leads communicate the voltage drop from one lead to the other, whether those are across contactors or different points on the same wire. When finding an undesigned voltmeter is most effective when used under load. You will see a massive voltage drop when you use a voltmeter under load; otherwise, you will see a much smaller voltage drop.


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