What is Voltage Testing?

Voltage testing is an essential procedure that should be completed before carrying out any work on an electrical installation.

Ensuring the absence of voltage can be vital for safety reasons and the main purpose is to limit the risks that live electrical circuits and equipment can pose to individuals.

Voltage testing is part of a broader process, consisting of four stages aimed at carrying out the electrical lockout of an installation:

1. Separation: De-energising the installation
2. Lockout: Using lockout systems for safe isolation
3. Identification: Identifying the device requiring intervention
4. Power: Ensuring the device is powered off

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.