The WL-283 Voltage Pen – 6878-28C is an electrical tester used to determine the presence or absence of voltage in electrical circuits. Such pens usually allow users to test the voltage in a circuit. The tip of the pen detects the presence of voltage and notifies the user, usually with an LED light or buzzer. These pens are often used in a variety of applications such as electrical maintenance, repair and hobby electronics. The model 6878-28C may be the product code of a specific brand or manufacturer. In this case, the features and functions of the pen may vary according to the brand’s standards and model.