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What is A Line Tester And How it Works

A line tester is an electrical tool used to test the presence of current and to identify phase / live wire in electrical installations. When the metal tip of the tester comes in contact with a live circuit, a small light encased inside the handle of the tool starts glowing.

If you dissect any electric line tester, you’ll come across components like a metallic cap, spring, neon lamp, resistor, metallic rod, and insulating plastic body. Each of these parts plays a crucial role in the functioning of a line tester.

line tester working diagram earthing

The above diagram shows how the line tester and the parts involved function.

Cylindrical Rod: It is flattened at the tip so that it can also be used to tighten screws. The tip is inserted into the socket cavity to test for the presence of electricity. The inner end is connected to a high-value resistor. They come in different lengths with “+” and “-” end tips. Except for the tip end area, the rest of the cylindrical rod is covered with a translucent plastic body.

Resistor: Here the role of the resistor is to reduce the electrical current to a safer level. If the operating current is passed directly through neon light, it will get burned and the person will experience an electric shock.

Neon Lamp: A neon lamp consists of a small glass capsule containing a mixture of neon and other gases at low pressure and two electrodes (an anode and a cathode). When an electric current is passed through the neon lamp, it starts to glow. It serves as an indicator to signal the presence of electricity. One terminal of the neon lamp is connected to a resistor, the other to a metallic spring.

Spring: As already mentioned, one terminal of the neon lamp is connected to the metallic spring. It is used to make the necessary connection between the neon lamp and the metal cap. Using springs instead of metal rods saves additional material costs and ensures better and more durable contact between them.

Metallic Cap: The metallic cap is threaded to allow tightening of the internal components between the rod and cap.

These components are insulated with a translucent plastic body to provide isolation from the outside environment and structurally support it.

Working Of Line Tester

When the tip of the line tester is plugged into an AC power source, the metal cap will make direct contact with the operator, completing the circuit. When the circuit is closed, electricity begins to flow and the filament of the neon lamp begins to glow.

The resistor reduces the high operating current and a reduced current flows through the neon lamp connected to the cap, which is in direct contact with the person operating it. Furthermore, the reduced current flows through the body to the earth and thus closes the circuit.

Now a big question arises, why don’t we experience electric shocks? As mentioned, the resistor reduces the electrical current to a safer level so that neon lights can glow while protecting the operator from electric shock

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