Get ready! We’re going to start with the basics of how to use and read a multimeter. When we’re done, you’ll have a firm grasp on the essential functions and benefits of this indispensable tool so you can bang out those projects you’ve been putting off. Or better understand how to use your multimeter on the job.
Not only is a multimeter the nuts and bolts for an electrician, but also for any homeowner who wants to check the wiring around their house or pull off some of their electrical projects.
And, for your convenience, we’ve reviewed the best multimeters for electricians to help you choose the best one for your needs.
With this easy-to-use device, even a beginner can measure their appliances, outlets, fixtures, and breaker box’s critical electrical characteristics.
What is a multimeter?
A multimeter is a handy tool that you use to measure electricity, just like using a ruler to measure distance, a stopwatch to measure time, or a scale to measure weight. The neat thing about a multimeter is that unlike a ruler, watch, or scale, it can measure different things — kind of like a multi-tool.
Most multimeters have a knob on the front that lets you select what you want to measure. Below is a picture of a typical multimeter. There are many different multimeter models; visit the multimeter gallery for labeled pictures of additional models.
What can multimeters measure?
Almost all multimeters can measure voltage, current, and resistance. See the next section to explain what these terms mean, and click on the Using a Multimeter tab above for instructions on how to make these measurements.
Some multimeters have a continuity check, resulting in a loud beep if two things are electrically connected. This is helpful if, for instance, you are building a circuit and connecting wires or soldering; the beep indicates everything is connected and nothing has come loose. You can also use it to make sure two things are not connected to help prevent short circuits.
Some multimeters also have a diode check function. A diode is like a one-way valve that only lets electricity flow in one direction. The exact function of the diode check can vary from the multimeter to multimeter.
If you’re working with a diode and can’t tell which way it goes in the circuit, or if you’re not sure the diode is working correctly, the check feature can be quite handy. If your multimeter has a diode check function, read the manual to find out exactly how it works.
Advanced multimeters might have other functions, such as measuring and identifying other electrical components, like transistors or capacitors. Since not all multimeters have these features, we will not cover them in this tutorial. You can read your multimeter’s manual if you need to use these features.
A Quick Recap on Volts, Amps, and Ohms
Before you start fiddling with your multimeter, you should understand a few basic concepts about electricity:
- Volts measure the voltage or amount of force “pushing” electrons through a circuit. If you use the common analogy of electricity as water flowing through a pipe, then volts would be water pressure.
- Amperes (amps for short) represent the current or how many electrons are flowing through a circuit. Using the water analogy, this would be the amount of water flowing through the pipe.
- Ohms measure the amount of resistance in a circuit; the higher the resistance, the more the circuit slows down the electricity, much as a clog would slow down water flowing through a pipe.
How to Use and Read a Multimeter to Measure Voltage
Follow these steps to measure the voltage with your multimeter.
- Identify whether the voltage you’re measuring is AC or DC. If you measure voltage in your home, it’s probably AC. If it’s in your car or a battery-powered device, it’s probably DC.
- Turn the selection switch to the appropriate voltage. AC voltage has a symbol that looks like a sine wave, the universal symbol for AC. The symbol for DC is a solid line with a dashed line below it.
- Plug the black probe into the COM outlet found on the multimeter.
- Plug the red probe into the jack, marked with a V.
- Turn your selector switch to the highest setting in the proper voltage category. Remember that mV stands for thousandths of a volt, so this is a very low setting.
- If you’re testing AC voltage, you should be wearing safety gloves. Gloves are always a good idea when working with electricity.
- Power up the receptacle or component for which you are testing voltage by either closing the breaker in your breaker box, turning the ignition in your car, or turning on the battery-powered device.
- Touch the black probe to the terminal on one side of the component you’re measuring and the red probe to the terminal on the other side of the component.
- If you’re not getting a clear reading, turn the selector to the next highest setting until you have a recordable number.
Other Features on Your Multimeter
But wait, there’s more. Your multimeter may have other functions, including a continuity check, which gives a loud beep if two things are electrically connected or, to put it another way, if they form a complete circuit.
The continuity symbol usually appears on your multimeter as a series of parallel arcs that look alike the standard “WiFi” symbol on your laptop or smartphone. If the circuit is complete, your multimeter will beep; if the items you’re testing aren’t electrically connected, it’ll stay silent.
Some multimeters can also check diodes like one-way valves that only let electricity flow in one direction. (The typical diode check symbol looks like a stubby arrow with a perpendicular bar across its tip.)
A few multimeters even can test other electrical components such as transistors or capacitors. In each of these cases, consult your owner’s manual for the details.
Setting the Dial on Your Multimeter
Once you understand the abbreviations and settings on your multimeter, you can start to use it. First, decide whether you’re measuring volts (V), Amps (A), or ohms (Ω) and whether your current is AC or DC, and then turn the dial to the appropriate setting.
If your multimeter is “auto-ranging,” which means it automatically detects the scale of your measurements, its dial will be relatively simple. But if your multimeter is “manual-ranging,” which means you have to give it a general idea of how big or small the measurements will be, each segment of your dial may be further subdivided into different scales or units of measure.
Because you want to be sure you’re getting an accurate measurement, set the scale a little higher than you expect to read, but not so high that your reading will be an indiscernible blip at the bottom of the scale. For example, if you’re measuring a 15 V circuit and your multimeter has 2 V, 20 V, and 200 V settings, you’d choose the 20 V setting.
Analysis of AC voltage measurements
- In general, all ac voltage sources vary from fluctuation in ac voltage over power distribution systems.
- When different from an expected measurement, voltage is more likely to be lower than usual.
- Generally speaking, the voltage measured in ac power systems should be within -10% and +5%.
- Voltage measurements were taken at various points in a system vary.
The only way to master this is to get out there and start doing it! Feel free to leave any comments or questions.