Voltage tester 101

Voltage testers measure the flow of electric current passing through a circuit, battery, or outlet; it is an easy-to-use tool that no electrical engineer, hobbyist, or electrician should be without. The device is typically used to verify whether a piece of equipment is operating correctly, if there is adequate voltage to power up, or if a circuit/wire is safe to handle.

Select a voltage tester
The neon two-wire model is the most common, least expensive, and reliable form of tester. It is made up of three parts: a casing with a test bulb, a pair of insulated wires, and two probes attached to the ends of those two wires. One wire probe is connected to a ground reference and the other to where you are testing for current. It can detect between 0 to 500 volts of electricity.

Image courtesy of FamilyHandyMan

Alternatively, noncontact testers provide a means for detecting voltage without having to touch the actual live wire, an electrically charged and conductive wire. They perform a reading through a wire's plastic insulation, but the readings are inconsistent when used on wires covered by metal conduits. These testers are excellent for measuring voltage in receptacles and light fixtures as there is a decreased risk of accidentally touching a live wire with your finger.

Noncontact detectors are fast and easy to use. (Image courtesy of Ravica.)

Ensure the voltage tester is working correctly
Before testing the actual circuit, you must verify if the voltage tester is working properly. If using a two-wire tester, activate the tester and touch the probes against one another; this will cause the bulb in the casing to light up for as long as the probes maintain contact. Afterwards, test out a live circuit with a known voltage to ensure the reading matches – that’s it.

Select voltage type
Select what current type is to be tested: AC, alternating current, or DC, direct current. The variation depends on the power source; electricity generated by a power plant flowing to the wall sockets of your home will be AC, and electricity generated by solar cells, batteries, or fuel cells will be DC.

Using the two-wire voltage tester
Begin by placing one of the probes on a ground reference, which can be a neutral white wire, a box screw, or the neutral side of an outlet.
Next, place the second probe on the live wire; this is either the black or red wire, the shorter side of a plug, or the hot side of an outlet. If there's an electric flow, then the test blub will light up indicating live current.
Do note that the tester must be handled delicately to avoid touching a live wire with your hand under any circumstances.

Using the noncontact tester
A noncontact tester is extremely easy to use. Simply place the tip close to the circuit you wish to test, and the bulb will light if there's a live current.

Testing light fixtures for current is hassle-free with this device — all you have to do is poke the tester into the light socket. It's also a safe way to identify live wires when cutting into walls because it can perform a reading through plastic insulation.

Have questions about using a specific tool for your projects? Visit the TechXchange forums to discuss.