These days you\u2019d be hard-pressed to find a test meter that just measured Volts and nothing else. Everyone manufactures multimeters<\/strong> that measure volts, current, resistance, and possibly other things too (frequency, capacitance, temperature with accessory probe, etc.). But today we\u2019re just going to concentrate on making voltage <\/strong>measurements with our multimeter.<\/p>\n Plug the Meter Leads Into the Correct Meter Jacks<\/strong><\/p>\n This seems obvious, but this author has failed to do this many times. Shown below is a typical multimeter face layout. This is an actual meter Kele uses in training classes. It\u2019s a few years old but the functionality of the controls is the same as a modern multimeter. Note that your multimeter controls may be arranged somewhat differently or completely differently. No one likes to do it, but you might want to actually read your multimeter instruction manual if it hasn\u2019t been thrown away\/lost by now!<\/strong><\/p>\n To read voltage, plug the black meter lead into the COM jack and plug the red meter lead into the V\/ohm jack.<\/p>\n Do not <\/strong>mistakenly leave the red meter probe in the mA or Amps jack and try to measure voltages between two points in a circuit. In the mA or Amps mode the meter leads essentially look like a direct connection and you will be shorting out the two measurement points in the circuit. Bad things can happen. Since we are discussing voltage measurements today, that\u2019s all we\u2019re going to say on the subject. You have been warned.<\/p>\n Set the Meter Selector to Volts<\/strong>\u00a0<\/strong><\/p>\n The meter selector switch has different major areas for choosing whether you want to read voltage, current, resistance (ohms), or possibly other things. You need to move the selector switch to one of the positions in the Volts area (upper right area on our example meter).<\/p>\n Set Meter Range (Unless You Have an Auto-Ranging Meter)<\/strong><\/p>\n Our example meter has different voltage ranges to choose from based on the maximum voltage you expect to measure. Always choose the smallest range that\u2019s higher than the highest voltage you are expecting to measure. For example, if you are going to measure 24V then on our meter you would select the 200V range (because the 24V we want to check is higher than the next lower range which is 20V).<\/p>\n If you accidentally select a lower range than the voltage you are trying to measure, the meter won\u2019t be damaged, you\u2019ll get some kind of \u201cover range\u201d indication on the display. This can vary from meter to meter. Sometimes it\u2019s a row of horizontal dashes, sometimes it\u2019s \u201cOL\u201d for overload, or maybe something completely different.<\/p>\n The only way you should damage your voltmeter from overvoltage would be if you exceed the maximum rating for the meter. That value should be in the instruction manual and it\u2019s almost always printed on the meter face too. It\u2019s pretty high, typically something like 750V or 1000V, values you will probably never encounter in HVAC work.<\/p>\n If your meter has an Auto-Ranging function you don\u2019t have to worry about setting the range, the meter will figure it out for you. It usually starts on the most sensitive range and, if it sees an over-range condition, moves to the next higher range, etc. until it finds the most sensitive range that does not result in an over-range condition.<\/p>\n Auto-ranging is very handy. The downside is that it can take the meter longer to display a final stable voltage reading because it has to trial and error each time to find the right range. A fixed-range meter manually set to the correct range will stabilize to a usable reading faster since it doesn\u2019t have to experiment to find the correct range.<\/p>\n Set Meter for AC or DC Volts As Needed<\/strong><\/p>\n \u00a0<\/strong>If you set the meter to read DC volts and put the probes on an AC voltage source, the meter will read essentially zero volts (the readout might jump around the zero reading a bit).<\/p>\n If you set the meter to read AC volts and put the probes on a DC voltage source, the meter display will jump up momentarily and then \u201ccoast\u201d back down to essentially zero volts over time.<\/p>\n So be careful \u2013 an incorrectly set meter will make you think there is no voltage present when there really is.<\/p>\n If you are probing a \u201cmystery circuit\u201d and you\u2019re not sure whether the voltage between two points is AC or DC, you can try both settings on the meter to see which gives you a non-zero value.<\/p>\n Place the Meter Probes on the Circuit Points To Be Measured<\/strong><\/p>\n To make a voltage measurement, you do not need to disconnect anything in the circuit. You do that for current or resistance measurements (which we are not covering today).<\/strong><\/p>\n Remember to keep your fingers on the insulated probe handles, don\u2019t touch the metal probe tips with your fingers. You might know the voltage is supposed to be low (24V) but why take a chance in case you\u2019re mistaken or there\u2019s a short in the wiring?<\/p>\n In the case of AC voltage, there is no polarity to worry about, the signal will always read positive on the display no matter which way the probes are placed.<\/p>\n In the case of DC voltage, the red probe should go on the more positive point and the black probe should go on the more negative point. But if you should get it backward no harm is done, the meter will just display a negative voltage value, the magnitude of the reading will still be correct and you will know that the point with the black probe is actually the more positive point.<\/p>\n If the display shows an over-range condition, just move the meter voltage selector to the next higher range and try again.<\/p>\n![\"\"](\"https:\/\/assets.kele.com\/content\/wp-content\/uploads\/2022\/02\/multimeter-blog-resistance-2.png\")
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