What is a wire tester used for?

The flow of electrical current is measured by placing an electrical tester at two points in the circuit. A voltage tester is the simplest of these tools. It consists of a small neon bulb with two insulated wires attached to the bottom of the bulb housing; each wire ends in a metal test probe. This type of tester is always used with the current turned on to determine whether there is current flowing through a wire and to test for proper grounding. It is also used to determine whether adequate voltage is present in a wire. Look for a tester rated for up to 500 volts.

To use a voltage tester, touch one probe to one wire or connection and the other probe to the opposite wire or connection. If the component is receiving electricity, the light in the housing will glow. If the light doesn't glow, the trouble is at this point. For example, if you suspect an electrical outlet is faulty, insert one probe of the tester into one slot in the outlet and the other probe into the other slot. The light in the tester should light. If it doesn't, the outlet may be bad.

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To further test the outlet, pull it out of the wall. Place one probe of the tester on one terminal screw connection and the other probe on the other terminal screw. If the tester bulb lights, you know the outlet is malfunctioning -- there is current flowing to the outlet, but it isn't flowing through the outlet to provide power to the appliance plugged into it. If the test bulb doesn't light, there is no current coming into the outlet. The problem may be a blown fuse or tripped circuit breaker, or the wire may be disconnected or broken behind the outlet.

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A voltage tester is designed to test for the presence of an electrical current. It is different from a multimeter, which can perform the same basic test, but also measures the voltage, current, resistance, and more. Both devices are useful for home electrical system repairs, and they function essentially the same. However, a multimeter requires more preparation to connect the multimeter leads to the correct jacks, select between testing AC or DC current, and to move the rotary dial to the appropriate setting for the desired test.

This added complexity is more than you need if you are just testing an outlet, light switch, wires, or even a battery for an electric current. A simple voltage tester is more affordable and easier to use. Use this guide to learn how to use a voltage tester to check if power is off before starting an electrical project.

Safety Considerations

Whenever you are dealing with the home electrical system it's important to proceed with caution to help avoid accidental electrocution. A voltage tester is one tool that can help keep you safe while you work on the electrical system, but it's necessary to note that a voltage tester can give a false reading. If the batteries are dying or the voltage tester is faulty, it may beep or vibrate while testing a dead circuit.

However, the real risk is if the voltage tester doesn't beep or vibrate while testing a live circuit. For this reason, it's recommended to test the voltage tester before every use. Additionally, it's a good idea to wear insulated gloves that can help protect you from electric shock.

Before You Begin

Receiving a false positive on a dead circuit can be annoying, but isn't as dangerous as receiving a false negative when the circuit is still live. Before using the voltage tester on a circuit, outlet, or light switch that appears dead, test the voltage tester on an outlet that you know is live to ensure that the voltage tester is functioning properly. Typically, this is a receptacle that is already verifiably powering a lamp, microwave, radio, TV, or computer.

Turn the connected device on to ensure that the outlet is live and powering the device. After this quick check, turn the device off and use the voltage tester to check the outlet for an electrical current. The tester should flash, beep, or both flash and beep to indicate that the outlet is live. If the tester does not respond, then the batteries may need to be changed or the voltage tester may be faulty.

There are three main types of voltage testers. The most common option is a contact voltage tester, which uses two metal probes to test the flow of electricity. There are also non-contact voltage testers which can detect an electrical current from about an inch away, instead of coming into direct contact with the outlet or exposed wiring. A third type of voltage tester, called a receptacle tester, is made for testing outlets. This device plugs directly into a three prong outlet to provide information about the electrical current.