Voltmeters




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A voltmeter is one of the tools that are used by meter techs on an almost daily basis. So, what do we use the voltmeter for, how do we use the voltmeter and how do we interpret the readings on the voltmeter? Also, I wanted to make note that when I refer to a voltmeter I am referring to a clamp on type meter that can measure voltage, current and resistance.

As meter techs we use can use voltmeters for a variety of tasks. On of the most obvious things, of course, is to check the voltage inside of a meter base. But even more in depth than that, we use voltmeters to check each phase of a transformer rated installation to make sure that it is at the proper voltage, more on that later. We can also use a voltmeter to check the amperage on a circuit and we can use a voltmeter to check whether or not a fuse is good.

So, using most digital voltmeters now is pretty straight forward because most of them are multi-range. This means that if you are measuring voltage you only need to select whether you are going to be working with AC or DC voltage. The AC selection will look like a sine wave or a squiggly line. The DC selection will be a solid line above a dotted line. For 99% of what we do in metering we will use the AC setting to find voltage. To find the amperage on a circuit we will turn the nob to amps and use the clamp on section of the meter. We will clamp this around the conductor that we want to know how many amps is on.

To find out whether or not a fuse is good we can do two things. First, with the fuse still in place we can check the voltage on the top side of the fuse to see what it is and the we can check the voltage on the bottom side of the fuse to see if it is good. If the fuse is bad we should get voltage on the top side and we should not get voltage on the bottom side. Another way to check a fuse is to use the resistance function of the meter. Typically voltmeters have a function that will beep when we check the continuity. Select this function and then touch the leads of the voltmeter together to verify that there is a beep. If there is, once the fuse has been pulled out and is no longer connected to live voltage touch both ends of the fuse with the leads of the voltmeter. If the fuse is good you will hear the beep. If the fuse is bad there will be no beep and the fuse will need to be replaced.

A voltmeter can be a great tool to use but if you do not know how to interpret the information that the voltmeter gives you then you might as well not even use it. How do we interpret this information? First of all, if you are going to be checking voltage with a voltmeter you need to have an idea of what the voltage you should get when you check it. For instance, in the United States most homes are fed by a 12o/240v service. This means that if you put the voltmeter leads on the two phases coming in you will get 240v. If you check each phase to ground you should get 120v. I also want to note here that these numbers are nominal values and that most utilities guarantee plus or minus somewhere around 5%. This means that typically if the voltage coming into the house is between 228v and 252v or 114v and 126v the voltage can typically be called good.

Secondly, if you are going to check the voltage on a circuit you need to make sure that the voltmeter is rated to be used on the voltage of that circuit. Most digital meters now can go up to 1000v safely but there are some out there that only go to 600v. You need to make sure what you have before you use it on a live circuit.

If you are checking the amperage then you need to know what the wire will handle so that you will know whether it is overloaded or not. For instance, number 12 wire is good for 20 amps. So, if you check it and there are only 10 amps on it then you are good to go.

If you are looking for a good voltmeter, below is one that I recommend purchasing. It will do all of the things listed above and it is very accurate and not too expensive.

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