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How to Use a Voltage Tester? Non-Contact Voltage Tester

A Voltage Tester is a very useful test equipment/device for home owners, DIYers and electricians. Its main job is to test whether AC Voltage is present or not (in an outlet or a wire). There are different styles of Voltage Testers and all of them serve the same purpose. Some devices such as Multimeters can do other things as well. But what exactly is a Voltage Tester? What are the different types of Voltage Testers? How to use a Voltage Tester? We will try to find answers to all these questions in this guide.

A Brief Note on Voltage Testers

If you are a residential electrician or a home owner who does electrical related DIY stuff, then you must be familiar with basic test and measurement equipment. We call these devices as Testers and Meters.

Using these instruments, you can measure the amount of current flowing in a circuit (Ammeter), amount of voltage between two points in a circuit (Voltmeter or Voltage Tester) or check whether there is a continuous path for current to flow (Continuity Tester).

Speaking of Voltage Tester, it is a device that electricians use to test the presence of voltage at an outlet or in a wire. While some testers use lights and sound to represent the presence of voltage, others use a number scale to indicate an approximate amount of voltage around the object or surface.

Yes. They only indicate only the approximate values as they are not known for their precision or accuracy. Those that indicate voltage will do it for the following common voltages: 120 – 240V AC, 480V AC, 600V AC, 125V DC, 250V DC and 600V DC.

Apart from the main job of testing the presence of voltage and/or indicating an approximate voltage at a test point, you can also use a voltage tester to test for grounded conductors in a circuit, distinguish between AC and DC Voltage and also check for blown fuses.

Types of Electric Voltage Testers

As we mentioned before, there are several types of voltage tester devices. Here is a list some popular ones.

  • Non-Contact Voltage Tester
  • Digital Voltage Tester
  • Solenoid Voltage Tester
  • Neon Voltage Tester
  • Multimeter
  • Receptacle/Outlet Testers

Working Principle of Voltage Testers

The basic working principle of a voltage tester is it measures the electric flux due to electric field between the live and earth components of the circuit. But depending on the type of voltage tester (usually the non-contact variant), we can have a Capacitive or Magnetic Induction principle.

Capacitive Sensor

Non-contact voltage testers with a capacitive sensor element uses the concept of capacitive coupling to detect the electric field. When we place the tip of the tester near a power cord, wire or an outlet, a small current is capacitively coupled from the live wire to the tester (and back to ground).

If the tester detects this current, then they light-up an LED (some even start beeping) without actually making contact with the live wires.

This type is common in majority of non-contact voltage testers and also some multimeters that include a non-contact voltage testing feature.

Magnetic Induction

Another non-contact voltage tester principle is based on magnetic induction. The tip of the tester is wound with a tiny coil and when we bring this tip in the vicinity of an electric field, a small voltage is induced in the coil.

The tester detects this voltage and lights up (or activates a buzzer).

How to Use a Voltage Tester?

Let us now see how to use a voltage tester. We will learn the simple testing procedure with respect to four popular voltage tester devices: a non-contact voltage tester, contact voltage tester (two-lead electrical tester), a receptacle/outlet tester and last but not the least, a multimeter.

Non-Contact Voltage Tester

The main benefit of a non-contact voltage tester, is well, in the name itself, it doesn’t need to make any contact with the live wires or outlets to test for the presence of voltage. It is actually very easy to use this type of tester.

First, power on the non-contact voltage tester. Most testers come with a button, which you have to press (or press and hold in some devices) to power it on. There will be some sort of audio (like a beep) or visual (like an LED turning ON) indications to know that the device is on.

Now, to test for voltage using non-contact voltage tester, all you have to do place the tip of the tester on the subject/object you are testing. You can place the tip on an electrical cord, metal part of an appliance, a light bulb, a circuit breaker or a light switch.

Two-Lead Electrical Tester

In contrast to the non-contact voltage tester, we have another type of tester that need to make electrical contact with the subject/object. These are known as Two-Lead (or Two-Probe) Electrical Testers.

As the name suggests, this type of device come with two probes: one red and one black. Before using the device, plug in the Black Probe into the ‘COM’ port of the tester and the Red Probe to the ‘+’ port of the tester.

Now, you can turn on the device. After turning on the device, take the Black Lead and plug in into the neutral slot (the longer slot in case of a receptacle or outlet) or make contact with neutral wire or bus bar.

Similarly, take the Red Lead and plug it into the live (hot) slot of the outlet (the short slot) or make contact with a hot wire.

Depending on the type of tester, you will get a visual indication in the form of LEDs or a value of the voltage on the digital display.

Electrical Outlet Tester

A Receptacle or Outlet Tester will usually not indicate any voltage but only a visual indication using lights to determine the wiring condition of an outlet. All you have to do is plug in the outlet tester in to a standard outlet and look for the lights.

Almost all outlet testers have three lights and depending on the problem (or the lack of one) a pattern of lights turn on. You have to refer to the manufacturers data regarding the lights but most popular one is shown below.

Indicator Lights Meaning Description
OFF Yellow OFF Open Ground Ground contact is not connected.
OFF OFF Yellow Open Neutral Neutral contact is not connected.
OFF OFF OFF Open Hot Hot contact is not connected.
Red OFF Yellow Hot Ground Reversed Hot and Ground are reversed.
Red Yellow OFF Hot Neutral Reversed Hot and Neutral are reversed.
OFF Yellow Yellow Correct Outlet is wired correctly.


A Multimeter, as the name suggests, consists of multiple meters in a single device. The most common meters in a typical multimeter are: Voltmeter, Ohmmeter and Ammeter. Hence, we can also use a multimeter as a voltage tester. If you are new to Multimeters, take a look at this How to Use a Multimeter guide.

Using multimeter is very similar to what we did in case of the two-lead voltage tester. Multimeter also has two probes that we have to use (by making contact) to measure the voltage.

If you have an auto ranging multimeter, then select the “AC Voltage” measurement setting (DC Voltage setting if you want to test DC Voltages such as batteries). In case of a manual multimeter, select the AC Voltage with highest possible value, which is 600V is most meters.

Make sure that you plug in the correct probes into the multimeter before making the leads contact with the test points. Insert the Black Probe into the COM port and the Red Probe into the Voltage port.

Now, similar to the basic electrical tester, use the Red lead with hot wire/slot and Black lead with neutral wire/bus/slot to measure the voltages.


A Voltage Tester is a very handy device for residential electricians and DIYers who work with electrical installation and repairs. It is a visual/audio indictor for presence of live voltage in an electric cord, an outlet, a light fixture or other places which are wired to mains. In this guide, we saw about voltage testers in general, different types and also how to use a voltage tester.

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