Purchased your first multimeter or planning to buy one? Wonder what type of measurements you can take with it and what’s the right way to use it?
You’ve knocked on the right door.
Knowing how to use a multimeter can be very useful for fixing technical issues at home. And in many cases, it allows you to save money in the end – whether it is because you don’t need to call your electrician for a faulty light switch or find that you only need to replace parts of your appliance/power tool instead of buying a new one.
That being said, electricity is dangerous. Unlike a trained person, who knows how to work safely with live equipment, that might not be your case. So please, always be extremely cautious when taking electrical measurements and turn the power off as much as possible.
We hope this guide will provide you with all the information you need to learn how to use a multimeter safely and do some electrical testing, diagnosing, and troubleshooting yourself.
Get Familiar With Your Multimeter
Keep reading to find out how to use a multimeter or click any section above.
Get Familiar With Your Multimeter
Probes
Multimeters come with a pair of probes – usually one red and one black probe. They’re made of a cable with a plug on one end to go into the multimeter and a pointy probe tip on the other end that you can use to probe electrical equipment.
Ports
Now lets’ look at the ports where you can plug the probes into the multimeter.
There are three – sometimes four – different ports with different labels, such as COM, V, Ω, mA, and 10A – or 20A.
- COM stands for common. That’s where the black probe is going to be plugged in. Conventionally, we connect that to the neutral, the ground, or the negative side of a circuit. But inverting the probes won’t create any problem. You’ll simply get a negative reading.
- V stands for volts. That’s where you’ll plug the red probe to measure voltage.
- Ω stands for ohms. Plug the red probe in the associated port to measure resistance.
- mA means milliamps. It is used to measure small amounts of currents.
- Finally, the A, 10A or 20A port is not going to be used often. It is used for measuring large amounts of current up to about 10/20 amps.
Labels and Features
Depending on your multimeter, you’ll have some or lots of symbols on the front that might be kind of overwhelming and confusing at first.
- The main symbols you need to know about are V for volts, A for amperes – or amps – which is the unit of current, and Ω which stands for ohm or the unit of resistance.
- Most multimeters allow you to measure both AC (V〜) and DC voltage (V⎓), but only some allow you to measure both AC (A〜) and DC current (A⎓).
- Some multimeters have auto-ranging and some don’t.
- Your multimeter might or might not have a separate on/off switch that you can use to turn the multimeter on and off. Remember to turn it off when you’re not using it in order to conserve the battery. More expensive multimeters usually have an auto power-off feature. That feature will turn the multimeter off automatically after a certain period of inactivity.
How to Use a Multimeter – Measuring Voltage
Testing Batteries
Testing a battery allows you to know whether it has been drained or is still good.
Here, we’ll take the example of a 1.5V AA battery.
- Plug the black probe into the COM port and the red probe into the V port.
- A battery uses direct current. So set the dial on your multimeter to V⎓ (V DC) if it has auto-ranging, or somewhere in the V⎓ range – don’t worry about the exact number yet.
- Touch the negative side of the battery with the black probe and the positive side of the battery with the red probe.
- If your multimeter has an auto-ranging function – usually, that’s when the word “auto” appears on the screen -, you’ll directly get an accurate reading.
- If it doesn’t, you’ll need to manually select the range that matches best what you want to measure.
- Here is a rule of thumb that you should keep in mind as it is applicable to all measurement types: The closer the expected measure is to the selected range, the more precise and accurate the measurement will be.
- When you already know what voltage to expect, just select the range closest to it. Here, we know that the battery voltage should be around 1.5V. So, to get the most precise measurement, we’ll need to use the 2V – or 2000mV – range.
- But, when you don’t know what voltage to expect, start with a higher range and progressively step down to the lowest ranges until you get the most accurate reading.
- With a range that’s too high, you’ll get a voltage measurement close to 0. With a 1.5V battery, if you select the highest range (1000V), you’ll get a reading of 0.01 kV – or 10V – which is way too high and therefore inaccurate.
- Now, set the dial to the 200V range, and you’ll get 01.5V which is already much better, but still not very accurate.
- Then, select the 20V range, and you’ll get an extra decimal displayed. The reading will be something like 1.58V. That’s much better.
- But you can still get a more precise reading. Step down to the 2V – or 2000mV – range and you’ll get a very accurate measurement expressed in mV like 1.578V – or 1578mV. That’s the best you can get.
- Now, if you were to set the dial to the lowest range (200 mV), you’d get a 1 with no other numbers on the screen. That means the range is too low for the voltage.
Testing Electrical Outlets
The voltage from an electrical outlet in a modern home will vary from 110 V to slightly more than 120 volts. As there is potential for electrical shock while performing this test, please be very cautious.
- To know whether your outlet is delivering the correct voltage, plug the black probe into the COM port, and the red probe into the V port.
- Set the dial to volts AC (V〜). Depending on the multimeter you use, you may also need to select the appropriate range. Here, it would be 200V AC.
- Insert the tip of the red probe into the shorter vertical slot of the outlet (hot) and the black probe into the longer slot (neutral).
- Read the measurement on the screen. You should get between 110 and 120 V.
- Now, you also want to measure the voltage between the hot and the ground. To do so, remove the black probe from the outlet while leaving the red probe in place (hot). Then insert the black probe into the small, rounded hole (ground) below the two slots. The reading should remain the same. If it doesn’t, the outlet might be badly wired or maybe the ground is missing.
- At this point, you should either cut the power off and check the connexions within the outlet or call an electrician.
How to Use a Multimeter – Measuring Resistance
Let’s see how to measure resistance with a practical example:
Testing Oven Resistances
Let’s say you’ve got an oven with a double grill element and you notice that the grill function produces less heat than it used to. You might then want to test the grill resistors to find out which one is faulty.
- SAFETY: Start by unplugging the oven from the electrical outlet.
- Then, access the resistor terminals at the back of the oven.
- Unplug the wires connected to the resistances. Remember which wire was connected to which resistance terminal.
- Rotate the multimeter dial to the ohm (Ω) position.
- If your multimeter has auto-range, you’re fine. If your meter has no auto-range but you already know what measurement to expect, set the range closest to your expectation. If you don’t know what measurement to expect, you’ll need to step down from higher to lower ranges, one after the other, to find the one that gives you the most accurate measurement.
- Now touch one resistor terminal with one probe and the other terminal of that same resistor with the other probe.
- Let’s say you get a reading of 26 ohms, which matches approximately the nominal value of the resistor stated in your owner’s manual. That means the first resistor is not faulty.
- Then you do the same thing with the second resistor but you get a reading of O.L – or 9999, I, or even L. This means Over Limit or Over Load: the resistance is too high to be measured. That reading means the second resistance is burnt/broken/interrupted. That’s the one you’re going to have to replace.
At first, measuring resistance can be a little bit counterintuitive. To understand better, remember this:
The lower the resistance, the easier it is for current to flow. And thus, the higher the resistance, the harder it is for current to flow.
The resistance of a wire is almost zero because a wire is the easiest way for the current to flow. And the resistance of a broken resistor is virtually infinite because there is no more connection at all between the two parts – the current can’t flow anymore.
This test could’ve also been done with a continuity check. That’s what we’re going to discuss next.
How to Use a Multimeter – Checking Continuity
Most multimeters provide a feature that allows you to perform continuity tests. A continuity test is used to check whether the current is flowing as expected. This allows for quickly detecting faulty wires or equipment.
Continuity means there is an electric connexion between two points. For example, there should be continuity between the two tips of a wire, from both sides of a single-pole switch that is turned on, or as above, between the terminals of a resistor.
SAFETY: Testing live equipment exposes you to various electrical hazards. So please, don’t take any risk and always turn off the system/power supply before testing continuity.
Now, let’s see how to do a continuity test with a practical example:
Testing an Extension Cord
Let’s say you want to test an extension cord. As damaged cords can potentially shock you or even start a fire, old extension cords should be tested occasionally.
- First, set the meter dial to the speaker symbol. With that setting, continuity is going to manifest as a continuous sound. A non-continuous sound means the connexion is faulty. No sound means there is no continuity.
- Unplug your extension cord from the outlet.
- Now, insert one probe into one of the holes on the female end of the cord, and touch all three prongs on the male end of the cord, one after the other. For each combination, listen whether you hear a continuous sound or not.
- Do this for all three holes on the female end of the cord.
- A continuous sound must be heard only when touching both:
- If you get continuity with any other combination, that means your extension cord is damaged and should not be used.
How to Use a Multimeter – Measuring Current
To measure a current, you need to connect an ammeter in series. That means you need to physically interrupt the flow of current to put the meter in line. The problem with around the home current measurement is you’re not going to “cut wires” only to be able to connect your multimeter.
- To measure a current safely, you need another type of meter, which is called a clamp meter. With a clamp meter, you don’t need to interrupt the flow of current.
- The only thing you need to do is set the dial to amps AC (A〜).
- Then open the clamp and put the wire you want to measure the current from inside the clamp.
- Close the clamp.
- Check the reading on the screen.
How to Use a Multimeter – Measuring Temperature
A multimeter is great for taking various electrical measurements. But it is to be noted that nowadays, most modern multimeters are capable of measuring temperatures provided you first get the compatible thermocouple – or temperature probe.
- Plug your temperature probe into the multimeter.
- Set the dial to the temperature mode.
- Press the select button to choose between Fahrenheit and Celsius.
- Measure temperature.
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