▷ How non contact AC voltage testers work? (2023)

A non-contact voltage test provides an easy and safe way of ensuring that electrical conductors do not have power without having to touch them.

The tester works by detecting the electric fields associated with AC voltages. These fields are usually present near the live conductors, hence the reason why there is no requirement for direct contact with the conductors.

The tester can be used by professional as well as consumers who can use the gadget around the house.

▷ How non contact AC voltage testers work? (1)

Figure 1: Testing power cable as a voltage | image: o-digital.com

(Video) How to Use a Non-Contact Voltage Tester

To check for a live conductor, the tip of the tester is inserted into the socket or placed near any other conductor under test. It is recommended to test all conductors, including the neutral, just in case there is a fault or incorrect wiring. Once the tester is placed near the live conductor, the electrostatic or magnetic fields induce a current that flows through the tester. This makes the device indicate the presence of a voltage by lighting up, making a sound or both.

The non contact testing works for almost all live conductors including those covered by insulation. However, the tester cannot test through a metal shielding or conduit.

(Video) How To Use a Voltage Tester | Ask This Old House

Principle of operation of a non contact voltage tester

There are two commonly used types of sensors; the capacitive coupled and inductively coupled testers.

Magnetic induction testers

The inductive coupled tester comprises of a sensor winding at the tip. When this winding is placed within the electromagnetic field, a voltage is induced in the winding and used to light or sound an alarm though a circuit within the tester.

A current will only creates an electromagnetic field if it is flowing. And since this tester works by detecting the magnetic field around conductors, it will only work in a if the conductor is part of a complete where current is flowing. As such, it will not indicate anything when there is an energized wire, but the circuit is not complete.

Capacitive sensor element

▷ How non contact AC voltage testers work? (2)

Figure 2: Testing if a socket is live | image: ECVV.com

(Video) Why don't perpetual motion machines ever work? - Netta Schramm

The tester uses capacitor coupling to detect an electric field and is capable of detecting energized conductors whether in a complete circuit or not.

For the tester to work, the person must touch the metal part of the tester so as to provide a ground reference and allow the stray capacitance from the live conductor to flow to the ground. Placing the tester near a live conductor forms a capacitive voltage divider network. This comprises of the parasitic capacitance between the sensor tip and the live conductor, and the capacitance between the sensor and the ground through the body of the user.

(Video) How To Fix Christmas Lights Half Out - Ace Hardware

Once the current flows to the ground, the tester will indicate the presence of the voltage through the light or sound.

Limitations on non-contact voltage testers

  1. The testers cannot work with DC voltages since the capacitors and transformers do not work with DC.
  2. The non contact voltage testers have limitations and do not actually measure the amount of voltage present. Instead, they only indicate the presence of an energized conductor, which may require further investigation, and precaution.


The non-contact tester voltage makes sure the power is cut off, and there’s no need to touch any wires. It is the safest way to do so. This is important in ensuring that power to the equipment is off before opening it for maintenance or a repair.

However, the testers cannot measure the amount of voltage and will only indicate the presence of an AC voltage.

Thanks for reading,
Steven Mill.

(Video) Why Does Your Internet Connection Randomly Stop Working?


How do wireless testers work? ›

Once the tester is placed near the live conductor, the electrostatic or magnetic fields induce a current that flows through the tester. This makes the device indicate the presence of a voltage by lighting up, making a sound or both.

What is a non-contact AC voltage detector? ›

A non-contact voltage detector is a device that can detect the presence or an electrical charge in a wire, cable, or piece of equipment without having to touch the object. Voltage detectors are primarily used by electricians and electrical technicians.

How accurate is a non-contact voltage tester? ›

These devices are not 100% accurate, but they do a pretty good job. You simply hold the tip near a suspected circuit, and it'll tell you if there's current or not.

How does an AC voltmeter work? ›

Simple AC voltmeters use a rectifier connected to a DC measurement circuit, which responds to the average value of the waveform. The meter can be calibrated to display the root mean square value of the waveform, assuming a fixed relation between the average value of the rectified waveform and the RMS value.

How do you use AC voltage meter? ›

How to measure ac voltage
  1. Turn the dial to ṽ. Some digital multimeters (DMMs) also include m ṽ . ...
  2. First insert the black lead into the COM jack.
  3. Next insert the red lead into the VΩ jack. ...
  4. Connect the test leads to the circuit: black lead first, red second. ...
  5. Read the measurement in the display.

How do you use a 2 way AC voltage tester? ›

Use the two-lead circuit tester to check for voltage. Place one lead on a live/hot wire (usually black, but can be any color other than green or white) and the other on a neutral (white) or ground (green or copper) wire, and the tester's light will turn on. This confirms that you have a good, complete circuit.

Can you measure voltage wirelessly? ›

The Wireless Voltage Sensor is ideal for exploring the fundamental concepts of electricity, voltage, and basic circuits. It measures voltages up to ±15 V with built-in overload protection, and features high-speed sampling rates when used with a USB connection.

Do non contact voltage testers work on DC? ›

Test quickly for energized circuits, detect AC and DC voltages with non-contact volt detectors available from Specialized Products. They are safe and allow you to avoid exposure to high voltage electrical shock or personal injury.

What is wireless voltage detector? ›

The wireless AC voltage detection sensor can interface. with other devices to detect voltage from 24 VAC to 500. VAC. The sensor notifies of the presence or absence of. voltage.

How does a neon line tester work? ›

Working Of Line Tester

When the circuit is closed, electricity begins to flow and the filament of the neon lamp begins to glow. The resistor reduces the high operating current and a reduced current flows through the neon lamp connected to the cap, which is in direct contact with the person operating it.

Will a voltage tester work on low voltage? ›

It's a dual-range unit, so it can detect standard voltage (outlets, regular wiring) as well as low voltage (doorbells, thermostats, irrigation wiring). Most testers detect only standard voltage.

Can a non contact voltage tester work through drywall? ›

Q:Can it detect voltage from wires behind drywall? A: Not really, the tip typically has to be within 1/2” - 1/4” of the hot wire to sense electricity.

What is a NVC detector? ›

Built-in Non-Contact Voltage (NCV) Detector allows for quick detection of live voltage. Convenient LED flashlight illuminates dimly lit area.

What is AC voltage sensor? ›

The AC voltage sensor is used to indicate the presence or absence of line voltage. The AC Voltage Detector indicates an ALARM/NORMAL condition in software and also via an LED mounted on the sensor.

Can you touch a live wire with a voltage tester? ›

One of the easiest ways to know if a wire is live is to use a voltage checker or a current checker. These are simple devices that you can touch to any wire, and it will tell you if there is electricity running through it.

Can a non-contact voltage tester give a false positive? ›

Now that you have a better understanding of capacitors and how non-contact voltage testers work, it's important to understand that they can provide false positive results sometimes.

Do non-contact voltage testers work through walls? ›

They're called "non-contact", but that means no electrical contact (i.e. they don't have to touch the bare wire). You'll just about have to touch the tool to the insulation of a wire for them to work properly, so it's not likely you'll be detecting wiring within any type of wall with one of these tools.

What are the two types of AC voltmeter? ›

Electro dynamometer type voltmeter: The voltage of both AC and DC circuits is measured using this voltmeter and both the AC and DC measurements are normally calibrated the same way. Rectifier type voltmeter: These are commonly used to measure voltage in AC circuits.

How does AC analysis work? ›

AC Analysis is used to calculate the small-signal response of a circuit. In AC Analysis, the DC operating point is first calculated to obtain linear, small-signal models for all nonlinear components. Then, the equivalent circuit is analyzed from a start to a stop frequency.

What is the principle of AC ammeter and voltmeter? ›

Calibrating AC voltmeters and ammeters for different full-scale ranges of operation is much the same as with DC instruments: series “multiplier” resistors are used to give voltmeter movements higher range, and parallel “shunt” resistors are used to allow ammeter movements to measure currents beyond their natural range.

What voltage will an AC volt meter display? ›

ac voltage display input voltage range is AC 20-500V, measuring voltage range is AC 20-500V, voltage measuring error is 2V, working environment temperature range is -40-55℃.

How does the dual range non contact voltage tester work? ›

Klein Tools Dual-Range Non-Contact Voltage Tester automatically detects low voltage and standard voltage. A bright green LED will tell you the tester is working and also functions as a work light. The light flashes red and two distinct warning tones sound when either low or standard voltage is detected.

What is the most accurate device for measuring voltage? ›

Multimeter Method

The multimeter contains circuitry that allows it to be used as a voltmeter, an ammeter, or an ohmmeter. It is usually capable of measuring both AC and DC voltages of up to several hundred volts.

What is the best instrument that can measure voltage? ›

Multimeter. A multimeter or a multitester, also known as a volt/ohm meter or VOM, is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter may include features such as the ability to measure voltage, current and resistance.

How do you measure voltage without a voltmeter? ›

How : first you connect ammeter & the resistor in between phase & neutral. Then measure the current flow through the resistor with the ammeter, Then multiply resistance value & current magnitude and you will get the voltage.

What is the advantage of a non contact voltage detector over a voltmeter? ›

What is the advantage of a noncontact voltage detector over a voltmeter? It does not have to contact the energized electrical circuit to indicate voltage.

Do insulation testers use AC or DC? ›

The voltage applied for insulation resistance testing may be either AC or DC. However, DC voltage is always preferred over AC for insulation resistance test.

What is wireless AC current detector? ›

Introduction: Wireless AC Current Detector

In this circuit, an antenna (spring) is connected to the base of first transistor. When we place this antenna near an object that is AC energized, a small current gets induced into the antenna due to electromagnetic induction. This current triggers the first transistor.

What is the purpose of a voltage detection device? ›

Voltage detectors are a quick, inexpensive way to check for the presence of live voltage on ac circuits, switches and outlets before working on them.

Why do testers glow in line? ›

If the bulb glows, it means the current is passing through the wire and the device under test is functioning otherwise, the current is not passing through the device or line under test is faulty. High resistance in the tester allows only small amount of current passes through our body.

What is a neon voltage tester? ›

Neon Voltage Tester

Neon voltage testers, or neon circuit testers, tell you only whether voltage is present; they don't tell you how much voltage is in a circuit. They have a small body with a neon light inside and two short wire leads with a metal probe on each end.

Why neon is used in tester? ›

The tip of the tester is touched to the conductor being tested (for instance, it can be used on a wire in a switch, or inserted into a hole of an electric socket). A neon lamp takes very little current to light, and thus can use the user's body capacitance to earth ground to complete the circuit.

Can you test voltage with power off? ›

With the power shut off, simply connect a test wire to a circuit wire in one box, clip the lead to the test wire and touch the probe to the ends of the circuit wires in the other box. The bulb will light when you find the right wire.

Can you get shocked by low voltage? ›

Beware of Low Voltage Electric Shock

What they don't realize is that low voltage electric shock can be just as dangerous causing both external and internal injuries, even though there is no sign of visible damage. A low voltage electrical shock is typically caused by electric current of 500 volts or less.

How many volts can low voltage wire handle? ›

Low voltage wiring is designed to carry 50 volts of electricity or less.

How do you use a handheld voltage meter? ›

Touch the black lead of the voltage tester to the negative terminal, and the red lead to the positive terminal. If you get no reading on your meter, check to see if your meter has a switch labeled DC+ or DC-. Switch the position if it does. If it doesn't, reverse the positions of the red and black probes.

How does a voltage meter work? ›

A digital voltmeter (DVM) measures an unknown input voltage by converting the voltage to a digital value and then displays the voltage in numeric form. DVMs are usually designed around a special type of analog-to-digital converter called an integrating converter.

How should volt meter be connected? ›

Well, a voltmeter is hooked up in parallel because we want to know the voltage across a circuit element, so on either side. Voltage, remember, is defined to be the difference between electric potential at two points in space.

How do you measure AC voltage? ›

How to measure ac voltage
  1. Turn the dial to ṽ. Some digital multimeters (DMMs) also include m ṽ . ...
  2. First insert the black lead into the COM jack.
  3. Next insert the red lead into the VΩ jack. ...
  4. Connect the test leads to the circuit: black lead first, red second. ...
  5. Read the measurement in the display.

How do you connect positive and negative on a voltmeter? ›

To use your voltmeter, first attach the positive input terminal lead to the positive end of the circuit. Then attach the negative input terminal lead to the negative end of the circuit. The voltmeter will turn itself on and do the measuring automatically.

What are the steps in measuring voltage? ›

Using voltmeters to measure voltage is a fundamental, everyday skill used by electrical engineers in lab.
  1. Step 1: Plug in Cables. Get cables and plug them into the voltmeter sockets. ...
  2. Step 2: Set Multimeter to Measure DC Voltage. ...
  3. Step 3: Determine the Voltage to Measure. ...
  4. Step 4: Place Cables and Read Voltmeter.

What is the symbol for AC voltage? ›

Your multimeter will have two voltage symbols around the dial. One “V” symbol is for AC voltage. The other “V” symbol is for DC voltage. The AC voltage symbol will be a “V” with a “∿” over the V.

What causes touch voltage? ›

The connection of all exposed- and extraneous-conductive-parts, either directly or indirectly, to a common terminal, i.e. the main earthing terminal of the installation, leads to the creation of touch voltages in the event of an earth fault and hence to the shock risk.

How do you measure AC leakage current? ›

The leakage current is measured by applying a fixed voltage and measuring the voltage across the shunt that is a result of the leakage current. The reference design uses different switchable shunt resistances, which are switched on in a sequence to measure the insulation resistance.

How is step and touch voltage measured? ›

The step and touch voltages test is performed applying current between the ground grid and the auxiliary ground spikes and measuring the step or touch voltage with the test probes. With the STLG option, the current generation is performed using an overhead line to connect to the remote ground.


1. What To Check If Your Garage Door Won't Open - Ace Hardware
(Ace Hardware)
2. How to Troubleshoot Your Ceiling Fan | The Home Depot
(The Home Depot)
3. Homelink Not Accepting New Garage Door Fix
4. What To Do If Your Laptop Is Plugged In But Not Charging
5. Fix a Touchscreen that does not Respond to Touch or Responds Intermittently | @HPSupport
(HP Support)
6. Three Ways To Run A Three Phase Motor On Single Phase, And the Pro's and Con's of Each Method #065
(Jeremy Fielding)
Top Articles
Latest Posts
Article information

Author: Stevie Stamm

Last Updated: 04/03/2023

Views: 6181

Rating: 5 / 5 (60 voted)

Reviews: 91% of readers found this page helpful

Author information

Name: Stevie Stamm

Birthday: 1996-06-22

Address: Apt. 419 4200 Sipes Estate, East Delmerview, WY 05617

Phone: +342332224300

Job: Future Advertising Analyst

Hobby: Leather crafting, Puzzles, Leather crafting, scrapbook, Urban exploration, Cabaret, Skateboarding

Introduction: My name is Stevie Stamm, I am a colorful, sparkling, splendid, vast, open, hilarious, tender person who loves writing and wants to share my knowledge and understanding with you.