A non-contact voltage tester or detector is an electrical tester that helps to detect the presence of voltage. Voltage presence is valuable information to have when troubleshooting or working on a failed asset. The first tool you’ll reach for is a non-contact voltage detector.
Non-contact voltage testers (also known as voltage tester pens, test pens, or voltage sensors) are the safest way of ensuring that electrical conductors do not have AC voltage present without touching the conductors and exposing yourself to an electrical shock.
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 tester’s tip 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.
How to Use a Non-Contact Voltage Tester
Before using any non-contact voltage tester, make sure to read, understand, and follow all manual instructions and warnings. This will help you more familiar with properly using your tester.
The best practice of using a voltage tester requires three steps. First, find a known live system such as a port of a fixed lamp or an electrical system or outlet. This helps you verify that the tester is working correctly.
Then, use it to test the unknown system and repeat the test on a known live system. The best non-contact voltage testers will light up and make a sound to confirm that it has detected the presence of a voltage.
It’s important to check each wire before and after disconnecting it to ensure it’s not energized. When testing an electrical receptacle or outlet, the non-contact voltage tester’s tip needs to be placed on a smaller plug slot’s faceplate.
But it’s a good practice to test all outlets just in case they were wired differently, incorrectly, or on different circuits.
If the receptacle is connected to a wall switch, make sure that the light is on before you start testing. When testing power switches, unscrew and remove the power plate. Then place the nose of the tester on the screw sides of the switch.
When testing a three-way switch, test all screw terminals on both switches before switching.
When testing a light fixture, turn the circuit off at the main panel, and ensure that the light switch is turned on. Unscrew the light bulb and place the ac voltage detector’s nose in the center socket button.
If the light fixture has two switches as with a three-way switch, test with one switch in both the up and down position. Having a non-contact voltage tester in your toolbox can save a lot of time when testing to ensure that your electrical outlets work every time. Make sure to use the best insulation resistance testers if you need to measure the insulation surrounding your electrical circuits.
Non-contact voltage tester vs. multimeter
The difference between a multimeter and a voltage tester is the non-contact voltage tester only detects whether or not voltage is present. A multimeter can tackle many different measurements and tests, including measuring the voltage level on the wire.
Why Is Non-Contact Voltage Tester False Positive Results?
Non-contact voltage testers, or test pens, voltage sensors, and voltage tester pens as they’re also known, are a safe way to ensure that electrical conductors don’t have AC voltage present without the need to touch conductors and potentially getting an electrical shock.
Non-contact voltage testers work by detecting any changing electric fields surrounding an object conducting an AC or alternating current.
The best part about these testers is they don’t need to make direct contact with the conductor to test the electric field.
A person using the tester only needs to touch the top of the handle to provide a ground reference.
If there is AC detected, the LED will light up.
The non-contact tester detects any voltage present through capacitive coupling. To understand this fully, it helps to know how a capacitor works.
Non-Contact Voltage Tester False Positive
AC voltage detector pens have different types of false-positive readings. Each tester has different settings based on the intended use and manufacturer:
- Stray voltage is usually associated with dairies, but it might show up in some residential neighborhoods. It’s related to neutral connections within the utility supply lines.
- Static Voltage. On some occasions, the voltage tester won’t show any voltage even if it’s held still. But as soon as you move the tester through the component’s surface, it will give you a positive reading. This might be some residual voltage in your system and a sign that the grounding/bonding system isn’t working correctly.
- Ghost Voltages can be high enough to set off the device’s tester but have no current. Look for disconnected wiring that’s running parallel to the energized wiring.
How To Operate A Non-Contact Voltage Tester
Before using any non-contact voltage tester, it’s recommended that you read, comprehend, and follow all warnings and instructions from the manual.
This will help you ensure you’re using the tester properly.
The best way to use a voltage tester generally requires these easy steps:
- Find an available system that’s live, such as an outlet, port of a fixed lamp, or another electrical system. This will help verify your tester works correctly.
- Now, use it to test the unknown system by repeating the test you did on the known live system. A good non-contact voltage tester will use lights or sounds to confirm that voltage is present. Be sure to check every wire before and after disconnecting it to ensure it is not energized.
- Remember, when testing an outlet or electrical receptacle, the tester pen’s top needs to be positioned on the smaller plug slot’s faceplate.
- It’s also a great idea to test all outlets just on the off-chance they were wired incorrectly, on different circuits, or simply differently.
- When the receptacle is attached to a wall switch, ensure that the light is on before you do any testing.
- If you are testing power switches, unscrew and completely remove the power plate. You’ll then place the tester’s nose on the side of the switch where the screws are.
- Testing a three-way-switch requires you to test all screw terminals on both switches before switching.
- If you want to test a light fixture, cut the circuit at the main panel, and make sure the light switch is in the ON position. You’ll also need to unscrew the light bulb before placing the tester pen’s nose into the center socket button.
- When working with a light fixture with two switches such as a three-way, test with one switch in the up and down position.
Keeping a non-contact voltage tester in your toolbox can save a great deal of time when testing circuits. This will help ensure the outlets are working each time correctly.
Remember to use a quality insulation resistance tester if you need to measure the insulation surrounding your electrical circuits.
Now that you have a better understanding of how non-contact voltage testers work, it’s essential to understand that they can provide false-positive results sometimes.