How to Use a Multimeter to Test Voltage of Live Wires?

Most of us have come across the command- check the voltage of the wire. Have you ever wondered what it means? Checking the voltage of a wire means detecting the potential difference between the live wire and other wires. The process isn’t tough or tedious if you can do it correctly. However, there are a few cautions that you must remember. To check the voltage of a live wire, a multimeter is a device that you have to use. 

What is a live wire? 

Now, you must be wondering what a live wire is. It’s an electrical cable through which electricity can pass. A live wire is positive, unlike a neutral wire which is negative. Lives wires carry the maximum amount of voltage and can be extremely harmful if someone comes in contact with it directly. Hence, to ensure the safety of people, most electrical circuits also come with an earth wire. Read further to know how can you check the voltage of a live wire using a multimeter

The basic functioning of a multimeter 

A multimeter isn’t any normal device. It’s a specially built instrument that can measure voltage, electric current, the resistance of any cable or wire. It’s a versatile tool that’s needed wherever you have to measure electricity. It’s purposely designed to be effective and useful in measuring ampere, voltage, and ohm wires. Hence, a multimeter is also known as VOM- voltage-ohm-meter. 

If you are interested in knowing how this device helps one to check the voltage, you must know how it functions. Have you ever wondered how a multimeter looks like? Or if you know about its various parts and components, do you know what each part does? Let’s first go through their functions. 

An average multimeter has roughly three parts: a selection knob, a screen, and two, sometimes three ports. Sometimes there can be more than three ports too. The screen of an average multimeter comes with a four-digit panel. The selection knob allows people to choose the parameters which they want to measure. Lastly, the ports are used to plug in two probes. These probes are connected to the circuit or earth for the final testing of voltage, resistance, etc. Let’s now see how the different parts of a multimeter help us to get the voltage reading of a live wire. 

Steps to Use a Multimeter to Test Voltage of a Live Wire

Checking the voltage of a live wire means finding out the difference between any other type of wire and live wire. Any other wire can be the neutral wire or the earth wire. So, checking the voltage of the live wire means finding out the difference between the neutral or earth wire on one side and the live wire on the other. Remember that the difference between an earth wire and a neutral wire is always zero in an ideal situation. However, in the case of faulty wiring, the neutral and earth wires might conduct the same amount of electricity as the live wire. 

Below enlisted are the steps following which you can get the correct voltage reading of any live wire. Without further discussions, let’s dive into the details: 

1. Setting up the Multimeter

Before you can use it, you have to set it up properly. Firstly, turn the rotary dial towards the point marked V with an alternating symbol ~ beside it. Within that range, you would get multiple numbers that indicate the voltage range. 

Leave the dial at the number that’s higher than the lowest one. This step is important because choosing the right voltage range is important to get the most accurate reading. However, you don’t have to do this step with every multimeter. If your multimeter doesn’t have any reading on the scale, it’s an auto-ranging multimeter. In that case, all you have to do is fix the dial to the point marked V~ and leave it. The device would automatically set the correct range. 

Once selecting the right range is over, you need to connect the probes to the multimeter. Make sure you insert the black probe into the slot marked COM. Also, remember to put the red one into the slot marked VΩ.

2. Maintaining Safety 

When you are dealing with electricity flow as high as 120 volts or 220 volts, there are a few essential safety measures that you have to take care of.

  1. Remember to never touch a live wire with wet hands. When dealing with electrical instruments or devices, always wear insulating gloves if you only have to move the wire. 
  2. Switch the device from DC to AC mode every time you are measuring any electrical value in the circuit. 
  3. Set the range to the highest value. Always de-energize and discharge the electrical circuit completely before you disconnect or connect it to a multimeter. 

When you measure using a multimeter remember the following things: 

  1. Connect the multimeter in series if you have to find outflow of current. 
  2. Connect the device in parallel if you want to measure voltage. 

3. Set the Parameters

Multimeters are devices that are built to determine three electrical units: voltage, ohm, and ampere. So if you are to determine the voltage of the live wire, you must set the selection knob to voltage mode. 

  1. For measuring AC: set the knob at the point marked V ~. 
  2. For measuring DC: set the knob at the point marked V-

An average multimeter would be able to measure voltage within the range of 200 mV to 600 V AC or DC. 

4. Plugin Probes

After you have finished setting the selection knob as per the type of magnitude and current of voltage you are willing to find out, insert the probes in the appropriate ports. We have already mentioned that they have usually two, sometimes three, or even more ports. It depends on the type of multimeter you have.  

If your multimeter has three ports, the different ports are : 

  1. COM: this is the common port that’s used to measure the ground or negative of a circuit. 
  2. mAVΩ: if you have to measure voltage, current, or resistance, you must insert the probe in this port. 
  3. 10A: this port is used to measure currents of high amounts

In this step, you only need to identify the different types of ports and insert the probe in the right one as per your needs. 

5. Actual Testing

Now that everything is done, you can step ahead to test the voltage of the live wire. But, if you are willing to crosscheck if everything has been done properly, test whether the multimeter is functioning properly by using it on a live wire. 

For testing, put the red probe into the live wire. Next, take the black cable and put it on the neutral wire. Now follow the readings on the multimeter’s screen. Even if you put the black wire on the earth cable, you would get a similar reading.

After the testing is done and you are sure that the device is operating correctly, you can do the test finally to determine the voltage. If you place the red and black wire on the wrong cables, nothing dangerous would happen. If you misplace them, the multimeter would show the actual reading but in negative. That’s because a multimeter determines the voltage of a live cable about the common port. 

6. Taking the Reading

If you notice the display screen showing a voltage reading between the range of 110 volts to 120 volts, the fixture is live. However, if the display screen shows zero, it indicates that there isn’t any voltage in the cable. This means that there is no electricity flowing through it. 

Precautions to take while you determine the voltage of live wires

When you are dealing with electricity, you must be careful because electrical hazards might occur at any moment. 

  • If anyone touches a live wire accidentally, the human body starts conducting electricity to the ground. This direct flow of current can harm your body and sometimes can even cause death. Hence, for one’s safety, one must always wear safety insulating gloves while handling the current. Also, be careful to not allow the probes to short circuit. Otherwise, it might create sparks.
  • Also, remember to never deal with a live wire in wet hands. Water is also a partial conductor of electricity and can lead to a disaster. 
  • Make sure to carry a tester screwdriver. 
  • Test whether there is enough electricity on the wire before using the multimeter. Then proceed to determine the voltage or resistance or current passing through the live wire. 

It’s better to confirm whether there’s current in the live wire before proceeding to do anything. Thay way you can prevent chances of a hazard. 

We have listed the steps to be followed in detail. By now you must have understood that a multimeter is a useful device that comes in handy in several situations. So make good use of it in times of need and don’t forget to take precautionary measures!