Get ready! We’re going to start out 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 just 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 own 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 critical electrical characteristics of their appliances, outlets, fixtures, and breaker box.
Table of Contents
1. Multimeter Basics
2. Important Safety Advice
3. What Can You Use a Multimeter For?
4. Basics of Electricity and Electrical Units
5. Parts of a Digital Multimeter
6. How to Use and Read a Multimeter to Measure Voltage
7. How to Measure Current
8. How to Measure Current with a Clamp Meter
9. How to Measure Resistance
10. How to Calculate Power
So why is this tool called a multimeter? Well, it’s because it’s a combination of a voltmeter, ammeter, and ohmmeter giving you the power to measure:
- AC voltage
- DC voltage
- and more!
If you have some simple electrical work to do around the house, and you don’t want to hire an expensive electrician, why not give it a try yourself?
We’re going to show you all you need to know about using and reading a multimeter including:
- basic electricity refresher
- multimeter parts and terminology
- testing voltage
- checking current
- checking resistance
- measuring electrical power
Important Safety Advice
Performing any kind of electrical work has certain dangers, so you’ll need to protect yourself.
Before starting this type of work, take a few precautions for your own safety.
- Always know where your breaker box is and clearly label the individual breakers. Most electrical work should be done with the breakers off.
- Make sure your work area is well-lit (sunlight and battery-powered lights) and cleared of obstructions so that you can move freely.
- Wear protective equipment such as goggles, gloves, and long sleeves.
Your multimeter, by itself, is a safe piece of equipment. The steps above tell you how to use and read a multimeter in safe conditions.
What Can You Use a Multimeter For?
Now the multimeter is a pretty impressive tool that has a wide range of applications for several professions or purposes:
- Check the resistance of fuses in your car or appliances.
- Measure current to prevent breakers from tripping in your house.
- Use a multimeter in your HVAC unit to make sure the compressor is getting the right amount of electrical power.
- If your car is having trouble starting, you can check the ignition voltage with your multimeter.
- Test switches, outlets, and power cables to see if there are any problems.
- You can also use it to test old batteries, extension cords, and light bulbs without plugging them in.
- Troubleshoot any electrical problems in your home, car, or personal devices.
Basics of Electricity and Electrical Units
Electricity can be a complicated subject, and we understand how confusing it may sound when we talk about circuits, beakers, amps, and volts. A quick refresher will help you learn how to use and read a multimeter without difficulty.
Electricity performs work for us when it travels in a circuit. If this word sounds like the word circle, that’s because it’s analogous to a circle.
The current flows around that “circle” in a circuit beginning at the breaker or fuse in your electrical box and then returning on the neutral wire. Just so you’re aware, the neutral wire will be white.
As you know, if the circuit of current is ever broken, electricity stops flowing and lights, outlets, etc quit working.
So why would a circuit be interrupted?
One reason could be a loose connection or damaged wire.
Or, the circuit breaker could simply be doing its job. Fuses and breakers are designed to open the circuit If they sense that too much current is flowing through that circuit.
This protects the wire from overheating which would be a bad thing.
Anyway, your multimeter, correctly used, can help you diagnose and repair many of these troubles.
Voltage is easier understood as “pressure”.
Think of water flowing through a garden hose.
Is it just running out the end from gravity, or is it being pushed?
Somewhere a pump is pressurizing that water so it flows with force. We measure water pressure in psi.
Electricity is also “pushed” by a generator and we measure that “pressure” in volts.
The greater the force, the higher the voltage.
We also talk about electrical potential.
Going back to the water example. Imagine turning on a spigot but closing the nozzle at the end of a hose.
The hose is now under pressure, isn’t it? There is a force being applied even though there is no flow.
Could that pressure be measured?
In the water hose example, a pressure gauge calculates the force so you know the strength of the water current if allowed to flow. The gauge is comparing the pressure inside the hose with the atmosphere outside and telling you the difference in psi.
Likewise, electrical potential is the amount of force in a circuit available to push the electrical current if allowed to flow. Like the water gauge, your multimeter is a comparative device. It compares the difference in electrical potential between two points and then expresses that difference in volts.
Amps, which is short for “amperes”, is what we call the unit that measures electric current.
Wait – I thought that’s what voltage is!
Remember our water hose?
If the pressure driving the water (psi) is like voltage, then the quantity of water (gallons per minute) is like current.
When we speak of electrical current we are referring to the amount of electricity – not the force behind it. In essence, it’s about the number of electrons passing by a point over a given time period. Therefore that number is also important, and we call it amps (short for amperes).
Your multimeter can measure current (amps) too.
Let’s say your 15 amp breaker keeps tripping. It could be that there is too much load on that circuit.
Like 5 hair dyers being used at once.
You can use the amp setting on your multimeter to determine how much current is flowing through a circuit.
- Direct Current – what we refer to as DC
- Alternating Current – called AC
Tip: For the correct setting, you want to make sure you know which current you’re measuring before using your multimeter. Generally, a battery produces DC voltage (like your car or flashlight) and your home’s electrical service is AC voltage.
As the word implies, resistance is the tendency of a conductor to resist current.
Does water flowing through a hose experience resistance?
Actually it does.
There is friction between the water and the surface of the hose.
Also – if you kink a hose the resistance definitely increases. Likewise, no electrical conductor is perfect. When it comes to conductors, aluminum is very good, copper is better, and gold is way better. Still, there will always be some resistance.
The more resistance in a circuit, the harder the voltage has to work for current to flow.
Fun Fact – Some resistance is planned. A resistor is often the whole point of having an electrical circuit in the first place. A lightbulb is a high-value resistor. It gives current such a hard time that the lightbulb gets very hot until it glows.
The amount of resistance in a circuit can be measured by your multimeter.
Now here comes another term – Ohms. An object or appliance’s resistance to electric current is measured in ohms and its symbol is the Greek capital letter, omega (Ω).
So, why would you need to measure resistance? One use for the ohms setting on your multimeter is to prove continuity.
Continuity means that current can flow uninterrupted from one point to another. If current can flow through a conductor from one point to another, we say that the conductor “has continuity”.
The ohms setting is a safe way of proving continuity before applying high voltage. We can also find:
- Damaged wires
- Short circuits
- Unidentified wires
- Failed devices
- Burned-out light bulbs
- And more!
Parts of Your Digital Multimeter
At first glance, the parts of a multimeter may look complicated. But with a little practice, you can quickly learn how to use and read a multimeter.
On the face of your multimeter, you’ll find the settings. The symbols around the dial might look foreign to you, but don’t worry. We’re going to explain everything here.
Generally, the dial settings are divided into three categories: voltage, current, and resistance. The voltage category might be further divided into AC voltage and DC voltage.
Multimeter dials are marked as following:
- Voltage categories are marked with a V for Volts
- Current category is marked with an A for Amperes
- Resistance category is marked with an (Ω) for Ohms.
Each category on your dial switch might have multiple settings for various ranges (Unless you have an auto-ranging meter. More on that later). If you’re measuring a low-current fuse or a small battery, you might have to switch the dial to a lower range to get an accurate reading. However, if you’re measuring voltage and current from your house outlets, then you’ll want to use a higher range.
It’s also important to understand the prefixes in front of the units:
- K stands for kilo and means 1000x.
- M stands for mega and means on million.
- m stands for milli and means 1/1000.
- (µ) stands for micro and means one-millionth.
Now, we’re going to put it all together:
- mV means millivolts, or thousandths of a volt
- kΩ stands for kilo-ohms, or 1000 ohms
- µA stands for micro-amps, or millionths of an ampere
Keep in mind that these prefixes are important for knowing how to read a multimeter.
You will find a digital LCD display above the dial. It should clearly read the values that you’re trying to measure. Next to, or above the numbers, you should make sure that the display also shows the proper unit symbol (mV, µA, or kΩ for example) for the electrical property you are measuring.
At the bottom of the multimeter, you’ll usually find the jacks for your testing probes. Your testing probes will be used to make contact with wires, terminals, or junctions.
Be mindful that the black probe always gets plugged into the common jack (#3, marked COM). It’s also known as the return terminal.
The red probe, or active probe, will get plugged into one of the other jacks, depending on the electrical property you’re trying to measure.
- The first red probe jack (outlet #1) is for current measurements between 0-4 amps and 10 amps, or for the frequency and duty cycle of the current. This jack should be marked with an A.
- The second red probe jack (outlet #2) is for current measurements between 0 and 400 mA, or for the frequency of this low current. This jack should be marked with an mA or µA.
- The third red probe jack (outlet #4) is for measuring voltage, resistance, diode, capacitance, frequency, duty cycle, and possibly temperature. It might be marked V, Ω, or the various symbols for diodes, capacitances, or degrees.
Now, just so you don’t get confused, your multimeter may have any number of additional buttons on the face. To understand the purpose of these buttons, it’s best to consult your operating manual.
Various multimeter brands include many different options and buttons. We won’t attempt to generalize their purpose here and now.
How to Use and Read a Multimeter to Measure Voltage
Follow these steps to measure voltage with your multimeter.
- Identify whether the voltage you’re measuring is AC or DC. If you are measuring voltage in your home, it’s probably AC. If it’s in your car or in 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, which is 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.
Example: Test an outlet receptacle with a multimeter: Let’s assume the outlet is secured in its place and all the wiring is connected correctly.
There should be 3 slots on this receptacle.
a. The top 2 vertical slots are for power (shortest slot) and neutral (longest slot).
b. The round slot below is ground.
If you’re using a manual multimeter, plug the red lead into the jack labeled V (volts) and the black lead plugs into the COM (common) jack.
Power up the receptacle and simply put the red lead into the power slot on the receptacle and the black lead into the neutral slot.
You should read 110-120 volts, assuming you’re in the U.S. If so, you’ve just proven you’re receptacle has 120 volts from hot to neutral. Hurray!
Now take the black probe and put it in the ground slot, you should read the same value. If so, you’ve just proven you have a clear path to ground. If either of these tests reads less than 110 volts, you now know something is wrong.
Let’s check your car battery with a multimeter: Switch to DC volts. Place the black lead on the negative post and red lead on the positive post. Did you read at least 12 volts DC? That’s good!
Now let’s check your alternator with a multimeter: Do the same test as above with the car running. You should be reading between 13 and 16 volts now. If so, your alternator is charging the battery as it should. Congratulations! Go have a beer.
- If you’re not getting a clear reading, turn the selector to the next highest setting until you have a recordable number.
Take note of these additional and important safety precautions before testing voltage.
- Make sure your probes are not damaged and that there are no exposed points in the test wires.
- Double-check that the red probe is plugged into the V outlet on your multimeter. Plugging into the wrong jack will dangerously damage your multimeter.
- Always start at the highest voltage range on your multimeter selection switch.
- If your multimeter probes have clips, this provides additional safety. You can clip the probes to the circuit before powering up the device or turning on the breaker.
How to Use and Read a Multimeter to Measure Current
Here are the steps you take to measure current with your multimeter:
1. Turn off the power to the circuit that you’ll be measuring.
2. Turn the selector dial to A which is current.
3. Plug the black probe jack into the COM outlet on your multimeter.
4. Plug the red probe jack in the appropriate current outlet, either the high current (A) or the low current (mA or µA).
Warning: If your measured current is higher than the low current limit, you can blow a fuse in your multimeter if you accidentally use that outlet.
OK let’s get real. Unless you are measuring a flame rod or thermocouple you very likely will not need to find thousandths or (good grief!) millionths of amps. So just stick the red probe in the A jack.
Now, this is where it gets messy. If you have a clamping meter, just skip all this and jump to the section on how to measure current with a clamp meter.
5. If you’re still reading, here’s what you need to do. The ammeter must be placed in series with the circuit to measure current. So the wire feeding the circuit must be opened and the meter probes placed across the gap. For example, if you want to measure the current in a circuit with an outlet receptacle, you could
a) Remove the live wire from the plug
b) Place the red lead from your meter on the disconnected wire
c) Place the black lead on the plug terminal where the live wire was before
d) Make sure you’re not touching either of the exposed parts of those leads
e) Turn the power back on
Now your meter is part of the circuit and is counting amps as they fly by.
Reminder: make very sure your meter is on the amps setting before doing this.
How to Measure Current with a Clamp Multimeter
A clamp multimeter is a multimeter with a special hinged jaw. We call it a clamping amp meter.
This clamping amp reader is a fast way of reading current on a conductor. Instead of using probes to touch exposed wires, a clamp surrounds a wire (even an insulated wire) and detects the current inside it through magnetic induction – reading the strength of the magnetic field around the conductor.
For most purposes, a clamp-on probe is the best choice because it’s easy and quick. You simply clamp the jaw around a wire, select amps on the dial, and the digital display will tell you how much current is passing through the wire.
Granted, you will get more accurate readings using probes since they can detect much smaller amounts of current such as milliamps and microamps. But I find that unnecessary for most household needs.
By not exposing wires, a clamp multimeter makes current reading much safer without the risk of electrocution. It also doesn’t require any interruption of the circuit, so you can keep your electronics running during testing.
Detecting magnetic induction is safer for the meter itself, and clamp multimeters can be used for much higher currents than a multimeter with probes. Make sure you are clamping on to only one wire at a time.
How to Use and Read a Multimeter to Measure Resistance
Since ohms are units of resistance, we begin by setting the dial to ohms to measure resistance.
Warning: Always turn off the power to the area your reading whenever you use the ohms feature. Otherwise, you run the risk of damaging your multimeter.
Here’s why: When you select the ohms reading, the battery in the meter sends a small voltage between your two probes, which is how the meter reads resistance.
The circuitry in your multimeter being used in the ohms setting is accessing about 3 volts DC from the batteries. If you were to introduce 100 volts through that circuit, you would surely damage something. Most likely you would only blow a fuse.
But who wants to deal with finding and replacing a little fuse inside their meter?
Follow these steps to measure resistance with your multimeter:
Note: Some of these steps are specific to manual ranging maters. If yours is auto-ranging – you can ignore steps #3-5.
- Turn off the power!
- Turn the selection switch to resistance, or ohms (Ω).
- Insert the probes into the proper jacks. The black probe will go into the third jack, labeled “COM.” The red probe plugs into the fourth jack.
- If the multimeter has an on/off switch (other than the selection switch), turn it on. Make sure the display activates.
- Set the selection switch to the highest resistance range to start your measurement.
- Touch the probe tips to the wires on opposite sides of the fuse or item for which you’re measuring the resistance. Resistance measurements will always be measured Your meter will measure the resistance it “sees” between the 2 probes. For example, If your probes are on either end of a fuse then it will measure the resistance of the fuse.
- If the display reads zeroes or a very low decimal, then adjust the selection switch to the next highest range until you see more numbers in the reading. This will give you a more accurate reading.
- After you have recorded your reading, turn off the multimeter to preserve the batteries.
- Finally, turn the selection switch back to the highest resistance units. This is for the protection of the multimeter, in case your next measurement requires greater current.
This is also a great way to prove a wire has continuity or is unbroken between two points.
If you were to measure resistance from one end of a wire to another, and if that wire is unbroken, what would you expect the meter to indicate? High or low resistance? It would be low since the wire is continuous. You would read zero or a small fraction of 1. If on the other hand, there is a break somewhere along the line, what would you read? It would be infinite resistance or OL which means overload.
Here are some additional tips to make sure you are taking a correct resistance measurement:
- The component you’re measuring should be removed from the circuit or appliance, to make sure you don’t accidentally measure the resistance through a different pathway.
- The component you measure should also be disconnected from any batteries or external power source. The multimeter batteries will provide the necessary power to test the resistance.
- If you’re testing a capacitor, make sure it’s discharged in order to prevent electrical discharge into your multimeter.
- Capacitors may take a moment to stabilize when you apply the multimeter probes. This is because the probes can actually charge the capacitor slightly.
- If you are testing the resistance of a diode, and you can’t get a reading, then switch the probes on the diode terminals. Diodes only conduct current in one direction, so if your probes are on the wrong terminals, you will either get a zero reading or an unreasonably high resistance reading.
- If you are measuring particularly high resistance and your fingers are in contact with the terminals, it’s possible that your fingers will affect the resistance reading. Just make sure you are not touching the metal part of the probes.
How to Use and Read a Multimeter to Calculate Power
A multimeter does not directly measure power or watts.
Instead, an appliance’s watts can be calculated rather simply by measuring the voltage and the current, and then multiplying them together.
Here are the 2 simple steps to determine watts:
- Carefully follow the steps above to measure voltage and current.
- When you have measured both values, multiply them together.
Now you have the watts.
The only way to master this is to get out there and start doing it! Feel free to leave any comments or questions.
And, if you found this article useful, please feel free to share it with others!