A non-contact voltage tester or detector is an electrical tester that helps to detect the presence of voltage. Voltage presence is useful information to have when troubleshooting or working on a failed asset.
The first tool you’ll reach for is a non-contact voltage detector.
To check for a live conductor, the tester’s tip is inserted into the socket or placed near any other conductor under test. It is recommended to test all conductors, including the neutral, just if 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 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.
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Principle of operation of a non-contact voltage tester
There are two commonly used types of sensors; capacitive coupled and inductively coupled testers.
Magnetic induction testers
The inductively coupled tester comprises 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 through a circuit within the tester.
A current will only create an electromagnetic field if it is flowing. And since this tester works by detecting the magnetic field around conductors, it will only work if the conductor is part of a complete where the current is flowing. It will not indicate anything when there is an energized wire, but the circuit is not complete.
Capacitive sensor element
The tester uses capacitor coupling to detect an electric field and detect energized conductors, whether in a complete circuit or not.
For the tester to work, the person must touch the tester’s metal part 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 the parasitic capacitance between the sensor tip and the live conductor and the capacitance between the sensor and the ground through the user’s body.
How do non-contact voltage testers work?
Non-contact voltage testers work by sensing a minimal amount of current capacitively coupled from the live circuit to the tester and back to the ground. Non-contact voltage testers light up when they detect this current without needing to make direct contact.
A built-in sensor at the tip of the tester detects voltage when touching a conductor, outlet, or supply cord. By holding the tool, you are the ground reference through capacitive coupling. When the tip glows red, and the unit beeps, you know voltage is present.
Why Do you need a non-contact ac voltage tester?
- A non-contact ac voltage tester is a must-have tool to test any electrical work around the home
- It does not need uncovered wires to detect voltage
- It allows you to work without coming into touch with the voltage source.
Non-Contact Voltage Tester vs. Multimeter
Non-Contact Voltage Tester:
- A voltage tester is designed to test for the voltage presence.
- It can identify AC, DC, or RF voltage.
- These testers are ideal for electrical engineering & household tools
- They only detect the presence of a live conductor
Multimeter:
- A multimeter can measure different factors, including the current, resistance, and voltage to inductance, humidity, and frequency.
- Multimeters can be used for multiple purposes.
- They are ideal for power supplies, domestic wiring systems, motor controls, electrical equipment, laboratory testing, and industrial work.
Restriction on non-contact voltage testers:
- The non-contact voltage tester is not ideal for DC voltages because the capacitors & transformers do not work with DC.
- They do not measure the actual amount of voltage present.
How to Use a Non-Contact Voltage Tester
A non-contact voltage tester is the safest way to make sure the power is off without touching any wires.
Before you open an electrical box, you should:
– cut off power to the outlet at the main electrical panel
– confirm you turned off the right circuit
This is where the non-contact voltage tester comes in handy. The tester will light up and make noise when it comes close to a hot (live) wire, even one that’s covered in plastic insulation. Note that it can’t test through metal conduit or metal sheathing.
Before using the tester, check its batteries quickly: shoving the tip into a live electrical socket or holding it against a lit lamp’s cord or bulb. You’ll hear continuous chirps or see a series of flashes to confirm the tester has detected voltage.
When testing a receptacle, just put the tip into the smaller (hot) plug slot. Of course, it’s always good to check the larger (neutral) slot if the receptacle was miswired.
Make sure you’ve checked all slots in the receptacle if they were wired differently or on different circuits, and if the receptacle is connected to a wall switch, make sure the switch is on during testing.
After you unscrew the receptacle, pull it out and directly test all the wires again to confirm they’re not live. It’s also a good idea to test any other wires reachable from the back of the receptacle.
When testing a power switch, unscrew and remove the cover plate, then place the tester’s nose against the screw terminals on the side of the switch. Once you confirm the wires aren’t live, it’s safe to unscrew the switch and continue testing other cables in the box.
When testing a light fixture, turn the circuit off at the main panel, and ensure the light switch is turned. Then unscrew the light bulb, and place the nose of the tester onto the centre socket button.
If the light has two switches (on a three-way switch), test with one switch in both the up and down position. Once you’ve confirmed the fixture isn’t live, it’s safe to unscrew it from the electrical box, pull it out, and test any other wires you see.
There you have the answer to how does a non-contact voltage tester work. This non-contact ensures you do not need to touch any wires when measuring the voltage presence. It is the safest way to measure the voltage indeed.
This is significant in making sure that the device’s power is off before opening it for maintenance. Nevertheless, a non-contact voltage tester only measures the AC voltage.
