What Is a Voltage Tester Pen?
A voltage tester pen is a tool used to check whether a power outlet is energized.
It resembles a flathead screwdriver, but it is not primarily used for tightening screws. When the tip makes contact with the point being checked, the lamp will light up if the point is energized, and will not light up if the point is not energized.
Depending on the object to be checked and the application, there are low-voltage types, high-voltage types, AC-only types, and dual-use AC/DC types.
Uses of Voltage Tester Pens
Voltage tester pens are used to check whether a circuit is active or not by directly touching the driver part of the circuit. Normally, electrical work and inspections are performed with the power to the electrical equipment turned off. However, if a worker touches the equipment while it is still live, he or she may receive an electric shock.
For this reason, it is a mandatory procedure to check for active and inactive power using voltage tester pens before any work is performed. In many cases, it is also used to identify the hot and cold sides of an outlet when connecting audio equipment.
Principle of Voltage Tester Pens
In voltage tester pens, there are two types of lamps that light up when active: neon tubes and LED lamps.
1. Neon Lamps
Neon lamps are a type of discharge tube that activates at relatively low voltages (60V~). The area around the electrodes emits a faint red glow (known as glow discharge) even with a small amount of current. Therefore, detection is possible by passing a small current from the active part through the human body to the earth (ground) and inserting a neon tube in the middle of the current.
A high resistance of 1 MΩ or more is connected in series with the neon tube to suppress the current flowing to the human body. On the other hand, the discharging tube is easy to use because it does not require a reaction or a power supply. However, its disadvantage is that it is lit by a small amount of current. As a result, its brightness is insufficient and it is difficult to check the lighting status in bright environments.
2. Led Lamps
LED lamps have the advantage of glowing brighter than neon lamps, making it easier to see the lighting status. However, they require an electronic circuit to turn on. When a person holds voltage tester pens and touches the tip of the pen to an AC active part, an extremely small current flows due to the electrostatic capacitance between the voltage tester pens and the human body, as well as between the human body and the earth (ground). The electronic circuit detects this current and turns on the LED.
However, a battery is required as the power source for the electronic circuit. If the battery is depleted, the LED lamp will not light up even if it is applied to an active part. Note that there is a possibility of misjudging that it is not an active part and that it does not react to direct current.
How to Select Voltage Tester Pens
In addition to the types of lamps mentioned above, there are two other factors to consider when selecting voltage tester pens.
1. The Strength of the Voltage That Can Be Measured
- Low-Voltage Type
Low-voltage tester pens are commonly used and can measure voltages of 300V or less. Since the voltage of wiring in a home is 100V or 200V, a voltage tester pen for low voltage is usually used. - High-Voltage Type
High-voltage tester pens can detect voltages from 2500V to tens of thousands of volts. Their main application is to inspect spark flags in cars, motorcycles, and other vehicles. When safety is important, such as in high-voltage facilities, a dedicated voltage tester pen should be used instead of a voltage tester driver.
2. Shape of the Tip of the Voltage Tester Pens
Voltage tester pens are shaped like a flat-blade screwdriver. This is because it is supposed to be inserted into an outlet plug. However, it is not recommended to use it as a screwdriver.
On the other hand, some screwdriver sets with interchangeable bits have a neon lamp built into the handle so that they can be used as voltage tester pens. Since these are originally manufactured as screwdrivers, they can be used for tightening screws.
Several types of bits are also available, including Phillips screwdrivers. When used as voltage tester pens, bits are selected based on the shape and size of the contact point. However, even in this case, bits with a positive shape are rarely used.