Saw my son ransacking my toolbox and he was playing with an electrical tester in the box. It comes in different names across the planet: line detector, phase detector, Live/Mains tester, etc. Thought today we can explore what it is and how its internals make it work.
An electrical tester is used to identify live or phase wires in electrical installations. It looks like any other screwdriver with a couple of extra components in the handle. You have a metallic probe that you can use to poke into the live terminals. It’s followed by a resistor of 1 Mega Ohm or more and a Neon bulb in series. The other side connects to a metal contact that sticks out of the back of the screwdriver. This is the point where you touch with your finger.
When the tester’s tip touches a live wire and the user touches the metallic cap, a circuit is completed. The current flows through the resistor and neon bulb, causing the bulb to glow. The resistor ensures the current is at a safe level, preventing any electric shock. It works even if you are not grounded on the floor directly because your feet/shoes will act as a capacitor with the ground. When you’re not adequately grounded, the Neon bulb emits a faint glow. However, if it comes into contact with a grounded terminal, it will glow brightly.
Are they safe? It’s a loaded question. I see them in use by electricians everywhere. The only problem is if there is a short on the resistor or if there is water ingress inside the screwdriver, then it can be dangerous especially if you are on a grounded plane. That’s a direct shock. Also, don’t go poking them on lines that can have higher voltages. The only suggestion I can give is to opt for a high-quality tester. A well-constructed tester will have insulation covering more than three-quarters of the metallic probe, and it will be sealed to prevent water from entering. These are cheap. So make sure you buy a good quality one. Always prioritize safety!
