HOW A LINE TESTOR WORKS

        

Testers are one of the simplest solutions, used to test current and voltage continuity in any circuit. Indispensible for any electrician, the testers are very simple and interesting devices. This article will explore the internal structure of one such commonly used circuit tester.

The user is required to be on the floor while using the tester so that he can serve as ground when current flows. In order to test the live wire, the user’s body must be in contact with the metal cap on the top of the screwdriver when the tester is put in contact with the wire. This completes a genuine electrical circuit and the bulb will light up once the tester senses voltage.

The tester shown above is a screwdriver cum testing circuit. The core of the tester is located near the head of the screwdriver. The plastic casing under which the tester circuitry is placed serves as an insulator.  As the metallic rod is the conductor part of the tester, in order to protect the user from getting an accidental electric shock, a thick sheath of plastic insulator is placed over metallic rod

The cap is followed by a spring. The spring has a dual functionality of acting as an earth wire and connecting the tester circuitry to the cap when screwdriver is placed inside a socket.

After the plastic insulating sheath is removed, the circuitry of the screwdriver can be seen clearly as shown above.

The above image shows the neon bulb connected to the spring through a wire.  It serves as an indicator of current whenever the metallic rod is plugged inside an active power source. The neon bulb gives output instantaneously and doesn’t get heated due to high voltage. The current requirement of the bulb is quite low and acts quite satisfactorily when circuit is grounded with the help of human body.

A resistor like one shown in the picture above is connected to the neon bulb from one end and to the metallic rod from the other.  The maximum current from the power source that can travel to the neon bulb is limited by the resistor.

The metallic rod is placed on the line upon which voltage has to be tested. Additionally, it serves the purpose of a screwdriver for general purpose use. In this way a very simple electrical circuit is used for debugging circuit breaks and tests their continuity