All About Multimeters

If you do any electrical work, a multimeter is a necessity. When it comes to ensuring safety, accuracy, and electrical code compliance, a multimeter will be your best friend. It helps electricians and DIYers identify wiring issues, certify that devices are working properly, and prevent accidents with potentially disastrous results. Although using one can seem intimidating and confusing, this guide will explain all about multimeters and shed some light on these handy tools.

What Are Multimeters Used For?

Multimeters are electrical testing devices that help users determine whether there is voltage present or measure several electrical properties. They can measure voltage (volts or V), current (amperage or A), resistance (ohms or O), and continuity (a consistent pathway for electricity to travel).

DIYers, professional electricians, electrical technicians, and electronics repair techs use multimeters. They can be used to test the voltage on a circuit to ensure that it’s dead, wired correctly, or carrying the proper amount of voltage. They can also be used to test for short circuits, how much current a device is drawing, how free-flowing a circuit is, if a resistor or diode is working properly, if relays are working, and much more.

Multimeters can also be used to troubleshoot electrical problems in low-voltage circuits, such as those in cars, motorcycles, trailers, and boats. They can also test individual components on PCBs (printed circuit boards) in electronics.

Types of Multimeters

While they all serve mostly the same purposes, there are a few different types of multimeters to know about. Each of these devices has test leads (the black and red wires) and the ability to test multiple types of electrical properties, but it’s important to know the difference.

Analog vs. digital multimeters

The two most basic types of multimeters are analog meters and digital meters. Analog meters have printed gauges with a physical needle that moves along the gauge. As the user tests a circuit, the needle moves across the face of the gauge to provide a value. Digital gauges have LCD screens that provide digital readings. As the users test a circuit, the gauge will display the value of the reading in numerical format.

Analog gauges can be difficult to read. Their faces are busy and the numbers are usually small, so accuracy can be a challenge. However, these devices are often necessary when it comes to sensitive electronics because they prevent the user from accidentally introducing electrical current to the circuit. Digital multimeters are much faster and easier to use, and more accurate, but they can damage sensitive electronics. In most cases, a digital multimeter is the best option.

Manual vs. autoranging

Multimeters need to know the range of the property that they’re measuring to provide an accurate reading. Some models require the user to set the multimeter to the range, which requires some knowledge and understanding of electrical properties. However, auto-ranging multimeters do this automatically, detecting the range on their own. This makes auto-ranging multimeters much more suitable for newer users, but often more than enough for pros as well.

Clamp meters

Some electrical meters have a clamp device that can clamp around a wire. This feature is designed to detect the amount of current flowing through an electrical conductor. Clamp meters are generally more suitable for professional use or higher-voltage device installations.

How to Use a Multimeter

Using a multimeter to test for the different electrical properties involved in a circuit is generally easy. However, there are some very important things you need to know first. The following steps should explain how to use the most commonly used functions of an electrical multimeter:

How to test for voltage using a multimeter

Voltage is by far the most popular use of a multimeter for most DIYers, and it’s also the easiest use. If you have a manual ranging multimeter, set it to the appropriate range, but most common digital multimeters should be auto-ranging today.

1. Insert the test leads in their appropriate ports. Place the red lead into the port labeled “VΩ,” and the black lead into the port labeled “COM,” or common.
2. Switch the multimeter to the voltage function, typically labeled “V.” If there are two V settings, one labeled “VAC” and one labeled “VDC,” you need to consider the circuit being tested: House circuits use alternating current or AC or Cars, motorcycles, boats, lawnmowers, trailers, and some electric motors use DC. Switch it to the appropriate voltage setting for the power type.
3. Holding the insulated handles, introduce the probes to the circuit. For an outlet, this typically involves first inserting the black probe into the left slot of an electrical outlet, and then placing the red probe into the right slot (if the outlet was wired properly). For vehicles, place the black lead on an unpainted metal object to ground the meter, and the red lead on the exposed electrical terminal or wire.
4. Read the display. If the meter is set properly, there should be a reading on the screen. This reading reflects the amount of voltage on the circuit.
5. Remove the test probes and shut off the device.

How to measure Ohms using a multimeter

Ohms is the unit of measurement used to describe the amount of resistance an electrical circuit is experiencing. Resistance can result from corrosion or another defect, or it can be purposely introduced into the circuit through a resistor or device. Here’s how to test for it:

Ohms testing introduces electrical energy into a circuit to measure how much it drops over the tested component or conductor. For this reason, it’s important that there is no existing power on the circuit. Be sure to shut off the circuit or remove the component from the power source and then test it for voltage using the steps to measure voltage with a multimeter.

1. Place the red test lead in the “VΩ” port, and the black test lead in the “COM” port.
2. Switch the multimeter to the resistance function, labeled with the Omega symbol “Ω”, which is the symbol for ohms.
3. Place the test probes on either side of the circuit or component. Make sure the probes are on the same circuit, otherwise the multimeter will not provide a reading.
4. Read the display. If the circuit is free-flowing with no obstructions or resistance, the meter will read “0.0,” and may even beep.
5. Remove the test probes and shut off the device.

How to measure amperage using a multimeter

Measuring amperage is more complicated than measuring voltage or ohms. But it’s a function that some DIYers might use to troubleshoot a circuit and test for overload, so it’s important to know how it works. The major thing to understand is that the meter must be connected in series with the circuit, which involves shutting the power off, disconnecting the conductor, and attaching the multimeter. Here’s a step-by-step guide:

1. Disconnect the power to the circuit. Test it by using the voltage test steps listed above.
2. Connect the test leads to the multimeter. Place the red lead in the port labeled “10A” to start. You might move this later in the test, but this is a safe place to begin.
3. Install alligator clips on the tips of the test probes. Most kits come with them, but if not, purchase a set compatible with your multimeter’s test probes.
4. Disconnect the component or circuit at one point, such as at a terminal screw or by disconnected wires held together by wire nuts. If you’re removing the circuit at a terminal screw, make a small test lead that connects to the terminal screw. The other end of the test lead should be exposed wire.
5. With the multimeter off, connect the alligator clips to the circuit by clipping them to the disconnected components. The multimeter should now complete the circuit.
6. Set the meter to the “A” setting. In some cases, there may be a separate “10A” setting, in which case, that is the setting to use.
7. Turn the circuit back on and read the display. The meter will display how much current the device is drawing.
8. If the number is very small (under 0.2), you’ll need to repeat the process after shutting off the power, moving the red test lead to the milliamp (ma) port, setting the meter to the lower milliamp settings, and restoring the power.

How To Use a Multimeter to Test an Outlet

If you need to know if an outlet was wired properly, how much voltage is on the circuit, or measure an outlet’s voltage for any other reason, these are the appropriate steps:

1. Start installing the test leads into the appropriate ports. The black lead should be connected to the “COM,” or common port. The red test lead should be connected to the “VΩmA” port.
2. Set the multimeter to the V or VAC setting. This is the setting used to measure voltage.
3. If your meter isn’t auto-ranging, set it to the appropriate voltage range. We’re expecting 110V to 120V on a common household circuit.
4. Using the insulated handles, place the black test lead in the left slot first. Then, place the red lead in the right slot. Check the reading, and then remove the red lead and then the black lead.
5. Place the black lead in the ground hole (the rounded hole under the slots), and then place the red lead in the right slot. The reading should be very similar to the first reading, which indicates that the outlet is wired correctly.

There are a few things that you should know when testing an outlet. First, if you place the red lead in the right slot first, the tip of the black lead will now have 110V or 120V power, potentially causing a shock or damaging components. However, if the outlet was wired incorrectly, the red lead could be powered if the black lead is in the left (correct) slot, so it’s always important to be careful when testing outlets.

Also, keep these problem conditions in mind:

• If the black lead is in the left slot and the red lead is in the right slot, and the reading features a “negative” symbol: the device is wired backward.
• If the readings between the left and right slots and the reading between the ground and right slots don’t match: there is a wiring issue or short.
• If the reading between the ground and left slot matches the reading between the left and right slot: the device is wired backward.

A Multimeter Is A Key Tool That Every Tool Kit Needs

A multimeter can be used to make sure circuits are safe, wired properly, and functioning the way they’re supposed to. And although a multimeter might seem confusing at first, it will be easy to use if you follow the steps listed above.