Last Updated on September 18, 2020
Live Wire: It’s an electrical wire through which there is a flow of electrical current. A live wire is positive whereas a neutral wire is negative – having high potential this differentiates from neutral wire through the voltage potential. A common example is the functioning of home appliances charged with current by the live wire, whereas the neutral wire carries the current back. Live wires are known to have the highest voltages & can prove to be fatal if you come in contact with them directly. To protect us from fatal incidents, mostly electrical circuits are provided with an Earth wire.
We’ve all heard the phrase, “checking the voltage of the live wire” or “to check the voltage of the live wire”, do you know what it really means? This is the process to identify the potential difference between the live cable & any other wire. In simpler words, we check for the potential difference between live & neutral wires or live & earth wires. It isn’t as tedious and dangerous as it sounds if done right. A multimeter is what makes the process easy & quick.
What is a Multimeter?
A multimeter is an instrument that is designed specifically to measure electric current, voltage & resistance over several ranges of value. It is a handy yet versatile tool that is needed whenever one needs to measure electricity. Purposely designed, it is an indispensable digital tool that excels in measuring Voltage, Ampere & Ohms in wires. Therefore, it is also known as a multi-tester or a VOM (Volt-Ohm-Meter).
This article aims to give you a detailed explanation of how to measure the voltage of a live wire using a multimeter. Without any further discussions let’s dig deep into the process.
For one to have a complete understanding of how to go about the whole process it is extremely essential to understand the basics. We know you’re wondering how does a multimeter look like? Or if you know how one looks like, you’ll be thinking about what each part does? That’s normal, completely normal. Let us explain to you all.
A standard multimeter has three parts – a screen, a selection knob & two, three, or more ports. Mostly multimeter’s screen comes with a four-digit panel. Apart from this, the section knob lets you select the parameter one wants to measure & the ports are used to plug in two probes that are connected to the ground or circuit for the purpose of testing. (1)
Steps to Use a Multimeter to Test Voltage of Live Wires
Step 1: Safety – the most important thing.
Few of the most essential points one needs to take care of while dealing with AC as high as 120 Volts or 220 Volts are:
- Never touch a live wire with bare hands. Wear an insulating glove even if you just plan on fixing or moving the cable.
- Switch the multimeter from DC mode to AC mode each time you want to measure an electrical value in the AC circuit.
- Start your testing with the highest current range.
- Don’t forget to de-energize & discharge the circuit completely before connecting or disconnecting a multimeter.
- You shouldn’t ever use a Multimeter to apply power to the circuit while measuring resistance.
To measure Current: Connect the Multimeter in series
To measure Voltage: Connect the Multimeter in parallel
Step 2: Set the Parameters
Milli-meters are designed to cater to three different parameters thus measuring voltage set the selection knob to Voltage mode.
To measure AC: Use the part labeled V and a wavy line to measure Alternating Current.
To measure DC: Use the part labeled V and a straight line to measure Alternating Current.
A typical Multimeter measures voltage within the range of 200 mV to 600 V AC or DC
Step 3: Plugin Probes:
If you are using a three-port multimeter, it comes with:
- COM: The common port to measure negative or ground of the circuit
- mAVΩ: To measure resistance, voltage & current up to 200 mA
- 10A: To measure very high currents
All you have to do is to plug the probes into the right ports according to what you want to measure.
Step 4: Actual Testing:
To ensure proper working, test the multimeter on a real live wire.
What to do for that?
1st Approach: Red probe on live cable & black probe on neutral cable. Check the reading appeared.
2nd Approach: Black probe on earth wire and red on Live Wire. You will get the reading.
Are you Getting a Negative Reading?
You might have accidentally reversed the positions of Black and Red probes. Always remember a Multimeter measures the voltage of live to the common (COM) port. (2)
Step 5: Taking the Reading:
There are two cases in terms of readings when you check a wire through a multimeter.
Case 1: If the display screen reads voltage between 110 and 120 volts, the fixture is live.
Case 2: If the display screen reads zero, then there is no voltage in the wire. In other words, there is no current flowing through the wire.
Wrapping it Up
It is completely okay to wonder why we need to check the voltage of the live wire. Let us answer this question for you. Electric hazards are extremely dangerous and can result in serious injury or even death in most cases thus being well aware of the current in the live wire is essential. This not only prevents accidental hazards but also makes sure you are cautious while handling them. Apart from this, it also helps in identifying the voltage to diagnose the reason for malfunctioning and thus the issue can easily be fixed.
In conclusion, a multimeter is undoubtedly an essential tool and can be used for many other purposes, such as measuring amperage (How to Tune an Amp with a Multimeter), resistance, and capacitance (How to Test a Capacitor with a Multimeter) among others.
(1) circuit – https://learn.sparkfun.com/tutorials/what-is-a-circuit/all
(2) COM – https://www.pcmag.com/encyclopedia/term/com-port