4 Easy Ways to Test Electrical Circuits with a Digital Multimeter

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A guide to testing voltage, amperage, resistance, and continuity
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A digital multimeter is a super handy tool for quickly measuring voltage, resistance, continuity, and current in many types of electrical circuits. It’s really easy to use a digital multimeter once you understand the various symbols on the dial. This wikiHow article teaches you how to use a digital multimeter with tips from master electrician Jesse Kuhlman.

Quick Steps

  1. Plug the black lead into the COM terminal.
  2. Plug the red lead in to measure V (volts), A /mA (amps), or Ω/Ohms (resistance).
  3. Set the voltage to auto-range or slightly higher than what's expected.
  4. Touch the red lead to the positive end of the circuit or electrical component.
  5. Touch the black lead to the negative end of the circuit or electrical component.
  6. Read the reading on the screen.
Method 1
Method 1 of 4:

How to Measure Voltage

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  1. Always plug the black test lead into the terminal that’s labeled “COM” for “Common.” Always plug the red test lead into the terminal labeled “V” for “Voltage,” since this is what you’re testing. [1]
    • Voltage is the speed or force at which electrons move through a circuit. Kuhlman likes to think of voltage like water pressure flowing through a water hose: The higher the force or "pressure" in an electrical circuit, the higher the voltage. [2]
    • Both AC and DC voltage are measured using the test leads in this setting.
  2. Turn the dial to V~ (or the V with a wave sign next to it) if you’re measuring AC voltage. Switch the dial to V⎓ (or the V with a horizontal line next to it) to measure DC voltage. [3]
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  3. Most digital multimeters have an auto-range function that automatically detects the voltage range. However, if your multimeter does not have this function, set the voltage to the nearest range that's higher than you expect. Look at the numbers on the dial and choose the setting that’s closest to the expected voltage of what you’re measuring while still being above that voltage. [7]
    • If you set the voltage range too low, you won’t get an accurate reading.
    • For example, if you’re measuring a 12V battery and there are settings for 2V and 20V on your multimeter, set the dial to 20V.
    • If you don’t know the voltage of what you’re reading, just set the multimeter to its highest voltage rating.
    • The standard voltage for most electrical outlets, lights, and light switches is 120V. Heavier appliances, such as your oven or clothes dryer, may plug into a 240V outlet. [8]
  4. Put the tip of the black probe on the negative lead of a battery or into the right side of a wall socket, for example. Put the red probe on the positive end of a battery or into the left side of a wall socket, for instance. [9]
    • If you’re not sure which end is positive and which is negative, try putting a probe on each end and seeing what the multimeter says. If it’s showing a negative number, your positive and negative are switched.
    • To avoid getting shocked, keep your fingers away from the tips of the probes when you’re putting them near a wall socket.
    • Keep the probes from coming into contact with one another, or you can generate a short circuit that could possibly cause an electrical fire.
    • Always hold the probes by the colored handles. They are insulated, which prevents shock.
    • The way AC electricity is wired in the home is through a "hot" wire that carries the electrical current and a "neutral" wire through which the electrical current returns through. The hot wire is usually black and the neutral wire is usually white. You also have a green wire, which is the ground. To test AC, touch the red probe to the hot wire and touch the black probe to the ground wire or a ground piece of metal. [10]
  5. Once your probes are connected to the positive and negative leads, you’ll get a reading on the multimeter telling you the voltage of what you’re testing. Look at the digital screen to find the reading and take note of it if desired. [11]
    • Looking at your reading tells you whether or not the voltage you're measuring is average or not. For example, if you measure the wall socket and the multimeter reads 100V, this is below the average (RMS value or root mean square value) of 120V, letting you know this wall socket voltage is low.
    • If you’re checking the voltage of a new 12V battery, the reading should be right around 12V. If it is lower or there is no reading at all, the battery is low or dead.
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Method 2
Method 2 of 4:

How to Test Current

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  1. Insert the black plug into the COM terminal. Put the red plug into amps or milliamps, labeled with A or mA, depending on the amperage of the current you intend to measure. Locate the Amps setting and turn the multimeter dial to it. [12]
    • Amperage measures the rate or number of electrons flowing through an electrical circuit. [13] Using Kuhlman's water hose analogy, while voltage is equivalent to the water pressure flowing through a hose, amperage measures the size of the hose. A larger hose allows more water to travel through at once. [14]
    • Your multimeter likely has two terminals for amps: one for currents up to 10 amps (10A) and one that measures up to roughly 300 milliamps (300mA). If you’re unsure of the range of amperage you’re measuring, place your red plug in the amps terminal.
    • You can always switch to milliamps for a more precise reading if necessary.
    • Some multimeters have two As, 1 for alternating current (AC used for residential power and represented by the wave sign) and 1 for direct current (DC used in batteries and wires and represented by a horizontal line with a dotted line under it). Direct current is the one that's most used for this reading.
  2. This allows you to use your multimeter as an ammeter to complete the circuit and measure the current. Unplug or otherwise remove a wire from the terminals it’s connected to on one side of the circuit, leaving the other wire connected to its terminals. [15]
    • It doesn’t matter which side of the circuit you disconnect. The point is to make a space to splice your multimeter into the circuit so it can act as an ammeter and tell you how much current is flowing through the circuit.
    • "Splicing in the multimeter" means that you're connecting the multimeter to the current going directly through the wires.
  3. Connect one probe to each of the terminals you just disconnected the wire from to splice it into the circuit. Read the screen to determine how much current is flowing through the circuit. [16]
    • It doesn’t matter which probe you touch to which side of the circuit. Your multimeter will give you a reading either way.
    • You can troubleshoot electrical circuits by splicing your multimeter into different sections of them. If one section gives you a lower current reading, it might mean a bad wire is inhibiting electrical flow.
    • If you initially test amps and get a really low reading, such as 1, switch to testing milliamps for a more precise reading.
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Method 3
Method 3 of 4:

How to Measure Resistance

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  1. Stick the black test lead plug into the COM terminal. The red test lead plug goes into the terminal labeled Ω, which is the symbol for ohms, the unit that resistance is measured in. [17]
    • Resistance measures how much a material obstructs an electrical current that flows through it. Different materials have different levels of electrical resistance. Materials that have low levels of resistance are called conductors because they allow electricity to flow through them more easily. Going back to the water hose analogy, resistance would be like adding a nozzle that restricts water flow through the hose.
    • The Ω sign is likely linked with the V sign, meaning the terminal to measure ohms and voltage is the same.
  2. Look for the Ω symbol on your multimeter dial area. Twist the dial to a number close to the expected resistance in this section. If you aren’t sure what the expected resistance is, set it to a number at the top of the scale. You can adjust it as you measure until you get a precise reading. [18]
    • For example, if you’re measuring the resistance of a wire, set the dial to just above 0. You can look up the expected resistance for different electrical components online or in an owner manual.
    • The Ω values on your multimeter can range from 200 to 2 million ohms, depending on the specific type of multimeter you have.
  3. Touch the tips of the probes onto each end of the resistor. Look at the multimeter digital screen to see the reading, which tells you the amount of resistance in ohms. [19]
    • If your multimeter is just reading “1,” you might need to increase the value of ohms measured by turning the dial so your reading is more specific.
    • Write down the reading if needed, noting the correct unit.
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Method 4
Method 4 of 4:

How to Test Continuity

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  1. If the device is still being powered, you can’t test for continuity. Make sure it is disconnected from all power sources before you proceed. [20]
    • The continuity option on your multimeter is for testing whether wires are still working or not. If you’re not sure whether a certain cord or wire still has a good connection, you can test this by measuring its continuity. This tests the connection between two points in a circuit.
    • Continuity is the presence of a complete path of electrical flow. For example, a brand-new electrical wire should have full continuity. However, if it is frayed or broken, it doesn’t have continuity because the electricity cannot flow through it. Using the water hose analogy, measuring continuity checks to see if there is a leak in the water hose.
    • This is a good way to see if cables are broken internally.
  2. Put the red plug into the terminal labeled as V, Ω, or with the sign for continuity, which looks like a sound wave. Insert the black plug into the COM terminal. Turn the dial to the picture that looks like a sound wave. [21]
    • A sound wave looks like a series of increasingly larger “)” symbols.
    • Instead of having a range of numbers in its area, the continuity option only shows one sound wave. Twist the dial until it’s pointing directly at the continuity sound wave to be sure it’s on the right setting.
  3. Place the black probe on one end of the component and the red probe on the other. Make sure that the probes are both touching the ends at the same time so the multimeter works properly. [22]
    • The component doesn’t have to be disconnected from a circuit to test for continuity.
    • It doesn’t matter which probe you put on which end of the component.
    • Examples of components you can test the continuity of are wires, switches, fuses, and conductors.
    • You have to be touching two conductive ends to test for continuity. For example, touch the probes to two bare ends of a wire.
  4. As soon as the two probes are touching the wire ends, you should hear a beep if the wire is working well. If you don’t hear a beep, this means you have a short in the wire. [23]
    • If you have a cut or burnt wire, your wire might have a short.
    • The beep is telling you that there’s almost no resistance between the two points.
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Expert Q&A

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  • Question
    Can a multimeter measure wattage?
    Jesse Kuhlman
    Master Electrician, Kuhlman Electric
    Jesse Kuhlman is a Master Electrician and the Owner of Kuhlman Electric based in Massachusetts. Jesse specializes in all aspects of home and residential wiring, troubleshooting, generator installation, and WiFi thermostats. Jesse is also the author of four eBooks on home wiring including "Residential Electrical Troubleshooting" which covers basic electrical troubleshooting in residential homes.
    Jesse Kuhlman
    Master Electrician, Kuhlman Electric
    Expert Answer
    No, that's actually one of the few things that a multimeter won't help you with. It can only measure amperage or current.
    Thanks! We're glad this was helpful.
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    Not Helpful 2 Helpful 4
  • Question
    How do you read the amperage if my multimeter is reading voltage?
    Jesse Kuhlman
    Master Electrician, Kuhlman Electric
    Jesse Kuhlman is a Master Electrician and the Owner of Kuhlman Electric based in Massachusetts. Jesse specializes in all aspects of home and residential wiring, troubleshooting, generator installation, and WiFi thermostats. Jesse is also the author of four eBooks on home wiring including "Residential Electrical Troubleshooting" which covers basic electrical troubleshooting in residential homes.
    Jesse Kuhlman
    Master Electrician, Kuhlman Electric
    Expert Answer
    All modern multimeters have an amperage and a voltage setting. They're really easy to read, but you do typically need to switch the setting, usually by turning a dial or pressing a button.
    Thanks! We're glad this was helpful.
    Thank you for your feedback.
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    Not Helpful 3 Helpful 8
  • Question
    How do I determine a current is grounded?
    Jesse Kuhlman
    Master Electrician, Kuhlman Electric
    Jesse Kuhlman is a Master Electrician and the Owner of Kuhlman Electric based in Massachusetts. Jesse specializes in all aspects of home and residential wiring, troubleshooting, generator installation, and WiFi thermostats. Jesse is also the author of four eBooks on home wiring including "Residential Electrical Troubleshooting" which covers basic electrical troubleshooting in residential homes.
    Jesse Kuhlman
    Master Electrician, Kuhlman Electric
    Expert Answer
    If you get a voltage reading of 120 volts or whatever you're normally reading between the hot and neutral, you know there is a ground there using a multimeter.
    Thanks! We're glad this was helpful.
    Thank you for your feedback.
    If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow
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      Warnings

      • Always hold multimeter probes by the colored grips, which are insulated to protect you from shock.
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      • Don’t let the probes touch when they’re both in contact with their respective parts of a circuit, or you can cause a short circuit and generate sparks.
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      • Never use a damaged multimeter with cracked probe handles or frayed wires.
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      References

      1. ↑ https://electrical-engineering-portal.com/measuring-resistance-voltage-current-digital-multimeter
      2. ↑ Jesse Kuhlman. Master Electrician, Kuhlman Electric. Expert Interview. 29 April 2020.
      3. ↑ https://electrical-engineering-portal.com/measuring-resistance-voltage-current-digital-multimeter
      4. ↑ Jesse Kuhlman. Master Electrician, Kuhlman Electric. Expert Interview. 29 April 2020.
      5. ↑ Jesse Kuhlman. Master Electrician, Kuhlman Electric. Expert Interview. 29 April 2020.
      6. ↑ Jesse Kuhlman. Master Electrician, Kuhlman Electric. Expert Interview. 29 April 2020.
      7. ↑ https://www.youtube.com/watch?v=g0YRkwv40r8&t=110s
      8. ↑ https://east-westelectric.com/all-you-need-to-know-about-240-volt-outlets/
      9. ↑ https://electrical-engineering-portal.com/measuring-resistance-voltage-current-digital-multimeter#measuring-voltage
      1. ↑ https://www.abelectricians.com.au/how-to-test-if-an-electrical-wire-is-live/
      2. ↑ https://www.allaboutcircuits.com/textbook/direct-current/chpt-3/safe-meter-usage/
      3. ↑ https://electrical-engineering-portal.com/measuring-resistance-voltage-current-digital-multimeter#measuring-current
      4. ↑ https://science.howstuffworks.com/environmental/energy/question501.htm
      5. ↑ Jesse Kuhlman. Master Electrician, Kuhlman Electric. Expert Interview. 29 April 2020.
      6. ↑ https://www.youtube.com/watch?v=7lwZkl0yBqA&t=96s
      7. ↑ https://www.youtube.com/watch?v=7lwZkl0yBqA&t=113s
      8. ↑ https://electrical-engineering-portal.com/measuring-resistance-voltage-current-digital-multimeter
      9. ↑ https://www.youtube.com/watch?v=TdUK6RPdIrA#t=4m18s
      10. ↑ https://electrical-engineering-portal.com/measuring-resistance-voltage-current-digital-multimeter
      11. ↑ https://ecampusontario.pressbooks.pub/multimeters101/chapter/continuity-test/
      12. ↑ https://ecampusontario.pressbooks.pub/multimeters101/chapter/continuity-test/
      13. ↑ https://startingelectronics.org/beginners/first-steps-in-using-a-multimeter/part-3/
      14. ↑ https://startingelectronics.org/beginners/first-steps-in-using-a-multimeter/part-3/

      About This Article

      Article Summary X

      To use a digital multimeter to measure voltage, start by putting the black probe in the common terminal and the red probe in the terminal that's marked for measuring volts. Then, set the multimeter to the kind of voltage you're measuring if it doesn't have an auto-range function. If you're measuring AC voltage, place the probes across the component. If you're measuring DC voltage or millivoltage, you'll need to place the black probe on the negative side of the component and the red probe on the positive side. Finally, check the display on the multimeter to see the voltage. To learn how to measure current and resistance using a digital multimeter, keep reading!

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