A voltage tester, regardless of the type, operates on a simple principle to determine the presence of voltage. This section offers insight into voltage tester operation to help you understand not just how to use a voltage tester, but also how do I use a voltage tester effectively and safely.
At its core, a voltage tester is a simple device designed to indicate the presence of electrical voltage in a system or a component. The underlying principle lies in Ohm's Law. This states that the current passing through a conductor between two points is directly proportional to the voltage across the two points.
When the probes of a voltage tester are connected to two points in an electrical circuit (commonly one end to a suspected live conductor and the other to a ground source), a closed circuit or loop is formed. This allows electrical current to flow from the higher potential to the lower potential.
Inside the voltage tester, this current passes through a known resistance. The voltage drop across this internal resistance is then measured and displayed on the tester's meter or screen. This provides the user with a reading of the voltage present. In some cases, for basic testers, this voltage may simply trigger a light or a sound to indicate the presence of voltage rather than providing a precise numerical value.
The design of voltage testers can vary. For example, a non-contact voltage tester detects voltage through insulation. It utilises capacitive coupling between the wire carrying the voltage and the sensor tip. When brought near a live conductor, the electric field influences the electric charge in the tester, causing an indicator (usually an LED light or a sound) to trigger.
Voltage testers are designed for safety. They are usually encased in a non-conductive housing to protect the user from accidental electrical contact, and they typically don't need the circuit to be operational to function, meaning they can be used in a wide variety of situations to ensure a system is safe to work on.