Multimeters are the electrician's go to tool for fixing problems in your home. Without a multimeter, it is next to impossible to fix an electrical problem. You can pick up a cheap multimeter anywhere however, if you're actually going to solve any problems you want a high-quality multimeter. There are a few Do's and Don'ts when it comes to multimeters if you want to perform repairs safely.
Do's
Understand what you're working on and how it works.
Know the dangers of electricity and how to stay safe.
Always verify your test leads are in the correct places on the multimeter for what test you are going to perform.
Check the safety rating of the multimeter you are planning to use.
When possible, perform all tests on dead/ de-energized circuits.
Don'ts
Never test resistance or continuity on a live circuit.
Never test amperage on a circuit if you aren't sure that it is under 10 amps.
Never remove the black test lead first as it could create an electrocution hazard.
Most quality multimeters have similar test features. You can measure voltages, continuity, resistance, frequency, and amperage. Some multimeters have additional measuring abilities that we aren't going to cover in this article, as this is for beginners. Below we will define each of these terms, plus a few more, so you have an understanding of which function to choose for your problem.
Voltage- measurement of electrical difference between 2 points
Continuity- measurement of the continuousness of a circuit (short vs. no short)
Resistance- measurement of the push back/resisting force of a circuit or wire.
AC current- voltage traveling in waves across different phases, found in all United States household wiring.
Now that you understand the terms that will be used in this article let's get to how to do your testing.
Voltage
Before attempting to measure voltage, we highly recommend using a reliable non-contact voltage detector to see if there is voltage on the circuit. To do this you simply turn on the non-contact voltage detector and move it near the hot, usually black, wire. If there is voltage present it should turn red and beep.
To measure voltage, you first need to make sure that your multimeter leads are in the correct position. Your black test lead always plugs into the black port labeled common. Your red test lead will be plugged into the red port with the letter V above it. As I'm sure you've noticed, there are multiple symbols above this port. The reason for this is because your red lead will stay in this port for all tests included in that group of symbols.
Once you have confirmed that your tests leads are placed correctly, turn the multimeter on by turning the dial on the front to the V setting. You should see a zero on the screen with a V at the right side of it.
On lower quality multimeters you will have to turn the dial to the V with the correct range. The ranges commonly include, 5mv-20mv, 20mv-1v, 1-50v, 50v-200v, and 200v-1000v. On these cheap multimeters, selecting the correct voltage range is important for taking measurements. However, with higher quality multimeters, like our favorite multimeter, an auto-ranging feature eliminates any guess work in finding your range.
Now that your multimeter is powered on and the selector switch is on the correct setting, you need to choose AC or DC mode. AC mode will be a wavy line and DC mode will be a solid line above a dotted line. You can alternate between the two by pushing the SEL or FUNC button. Remember, all household power in the United States is AC current.
After confirming all settings are correct, you're going to start your testing. We will quickly show you how to troubleshoot a receptacle for this explanation. First you need to insert the black probe into the large rectangular hole on your receptacle. This hole is on the left side of your receptacle, if your receptacle looks like a face. Now that your black lead is in, insert the red test lead into the smaller rectangular hole on your receptacle.
If the circuit breaker is on and the circuit is working correctly, your multimeter should show between 118v and 123v. If the multimeter is showing voltage in this range, then whatever your problem is, the receptacle isn't to blame. If your multimeter is showing no voltage, then you have a problem in that circuit. Now that you have taken this measurement be sure to remove the red test lead before the black. Then turn your multimeter off. If you are testing a GFCI receptacle, there is one more test that will need to be completed. We will explain this test in a future article.
For testing voltage on batteries, be sure to select the DC function of your multimeter. The symbol for DC measuring is a solid line above a dotted line. Always place your black test lead on the negative side of the battery and the red test lead on the positive side of the battery. As with AC measurements Always remove the red test lead before the black. This process of testing reduces the chances of electrical shock.
Continuity
Continuity tests are traditionally used for checking for short circuits. A short circuit is a circuit that has an incomplete or shorter than planned pathway. Extension cords and appliance power cords are notorious for developing shorts.
As with voltage testing, we highly recommend using a reliable non-contact voltage detector before performing a continuity test. To do this you simply turn on the non-contact voltage detector and move it near the hot, usually black, wire. If there is voltage present it should turn red and beep. Attempting to check continuity on energized, live, circuits could result in an explosion of your multimeter or electrocution. Once you have verified there is no presents of voltage on your device/ wire to be tested, you can proceed with testing.
Before you begin your continuity test verify that your test leads are in the correct holes. The black test lead should be in the black hole labeled common. The red test lead should be in the red slot labeled with a V as well as multiple other symbols. One of the symbols above that hole should resemble a sideways Wi-Fi symbol this is the audible continuity test symbol.
Now that your test leads are in the correct arrangement, you need to turn the dial on your multimeter to the setting that resembles a sideways Wi-Fi symbol. There will also be a symbol that resembles a horseshoe at this location. Once you have the dial set look at the screen on your multimeter and verify that the sideways Wi-Fi symbol is on the screen, as well as the letters OL. If the sideways Wi-Fi symbol isn't on the screen you will need to press the SEL or FUNC button, depending on your multimeter brand, until you see this symbol.
When your multimeter is correctly setup you can touch the tips of the test leads together. When the test leads are in contact with each other you should here a continuous beep. The OL that was previously on the screen should have changed to a value very close to zero.
If you do not here the beep, or if the value on the screen isn't very close to zero, then your test leads, or multimeter, are faulty and need to be replaced.
After completing the setup and testing of your multimeter functionality, you can then begin your diagnosis of whatever it is that needs testing. The basic idea of this test is that when the wire that is being tested is continuous, the multimeter will beep and show a value near zero. When the wire being tested is broken, or if it has a short, you will not hear a beep and the screen will show OL.
The simplest example of this test being performed would be on an extension cord. If you suspect an extension cord of having a short, a continuity test should be done. To do this you will want to bring both ends of the cord near each other. You should notice 2 or 3 different prongs, depending on the type of extension cord, on the male end of the extension cord. The different sizes on the male end should coincide with the female end. These different sizes represent completely sperate wires. When testing an extension cord for a short, be sure to test each complimentary size. Start with the smallest prong and hole.
Your multimeter should be powered on and on the correct setting by this point. First, insert either test lead into the smallest hole. Next hold the other test lead to the smallest prong. Note, test lead arrangement doesn't matter during this type of testing. You should here a beep as soon as you touch the smallest prong on the extension cord. If not, your cord has a short. Now that your multimeter is emitting a beep, you'll want to wiggle each end of the extension cord while maintaining contact with the prong. If the beep stays continuous throughout the entire test, the move on to the next hole and prong and repeat these steps. If any of the combinations has no beep, or if the beep came and went with the wiggle, then the extension cord has a short and needs to be repaired or replaced.
Resistance
Never test resistance on live circuits. We highly recommend using a reliable non-contact voltage detector before performing a continuity test. To do this you simply turn on the non-contact voltage detector and move it near the hot, usually black, wire. Resistance is the push back or resisting force that a circuit applies to electricity. Resistance is a similar principle to friction. Some circuits require a specific resistance to operate correctly. In such cases a component called a resistor is installed to achieve that desired level of resistance.
Copper has very little resistance naturally. This makes it an ideal material for carrying electricity where it needs to go as wires. However, as copper begins to age and see more use, the molecular structure begins to change. As the actual copper begins to deteriorate the resistance begins to increase. Rough environments can accelerate this process dramatically. Also, the more you use a wire, the faster it breaks down.
Whether you are testing a resistor, or the quality of a wire, the
process is the same. First ensure that your multimeter test leads are in the correct holes. The black test lead always goes in the black hole labeled common. Your red test lead goes in the red hole that has multiple symbols above it. The specific symbol that you are looking for, on the multimeter, dial resembles a horseshoe. This symbol is an abbreviation for ohms. The actual value of the measured resistance is expressed as ohms. So, ohms are the unit of resistance. This is similar to how Fahrenheit coincides with temperature.
You can find the ohms setting with a group of multiple other symbols. Then you will need to use the SEL or FUNC button until you see the horseshoe/ ohm symbol on the screen. If your multimeter is a good one, like our favorite multimeter, it is auto-ranging. In this case you can simply start testing. If you have a low-quality multimeter, then you will have to select the appropriate testing range for you test subject.
Now that your multimeter is setup correctly, and you have used a reliable non-contact voltage tester to verify there is no voltage, you can begin your test. First touch your two test leads together. The value on the screen should be very near zero.
If not, then your test leads, or multimeter, need to be replaced. Whether you are testing the condition of a particular wire, or testing the condition of an actual resistor, the test is the same. You simply place the black test lead on one end of the wire, or resistor, and the red test lead on the other. If the value on the screen shows near zero, then the wire is in good shape. For resistors, if the value shown on the screen is within 1% of the value printed on the side of the resistor, then the resistor is in good working condition. If the wire, or resistor, shows an OL on the screen, then the test subject is not in working condition and needs to be replaced.
Summary
Having a high-quality multimeter is crucial to receiving accurate test results. A reliable non-contact voltage detector is the most important item to keep you safe. Be sure to check the voltage safety rating of your multimeter and non-contact voltage meter before purchasing.
The three tests covered in this article are the most common tests that you will need to perform in your home. We hope you find this article helpful and most of all we hope this article can guide you through the safest way to do these tests. In the future we will post receptacle, light, circuit breaker, car battery, and many more troubleshooting techniques. Our goal is to save you money, as well as to keep you safe, while you perform your own household electrical repairs. Make sure to join our mailing list at the bottom of this screen so you don't miss our future content.
To get a high-quality multimeter and reliable non-contact voltage detector, click any hyperlink or image in this article. Need more information? watch the video below.
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