What will happen if the test lead is broken?
The interior of the test pen is generally composed of a high-resistance resistor, a neon tube, and a spring. The resistance of this high-resistance resistor is generally in the MΩ level. It is connected in series with the neon tube. Its function is to limit the current and avoid large leaks during testing. The current flows through the neon tube and the human body. The possibility of damage to the resistor is very small, but if there is a fault such as poor contact between the resistor, the neon tube and the spring, without knowing the fault, use the electric pen to measure whether the charged body has AC high voltage. If the neon tube does not light up (or the brightness is very weak), misjudgment may occur, which may cause electric shock to the user. In addition, if water accidentally enters the inside of the test pen and it is relatively humid, it is easy to get an electric shock when using the test pen to measure AC220V voltage. Therefore, before using the test pen, you should check the quality of the test pen and confirm Use it again if there is no problem.
When using a digital multimeter instead of a test lead to determine the neutral and live wires, you can adjust its range switch to the AC 200V voltage range, touch the black test lead to the ground or wall, and the red test lead to two wires respectively. If the red test lead touches zero line, the voltage displayed by the multimeter is very small, close to 0 volts. If the red test lead is in contact with the live wire, the voltage displayed by the multimeter is generally above tens of volts. Using this method to measure AC high voltage is safer, unlike a test pen where current will flow through the human body.
① Very dangerous!
② However, the danger does not occur when using a test pen to measure live wires. The high-resistance resistors used in electric test pens are solid-core resistors, also called volume resistors. They are divided into two categories: organic synthetic solid-core resistors and inorganic synthetic solid-core resistors. This type of resistor is made of a mixture of granular conductive materials, non-conductive powdery materials used as fillers, and adhesives. Granular conductive materials are carbon black and graphite; non-conductive powder materials are mica powder, quartz powder, glass powder, titanium dioxide (titanium dioxide powder), etc.; some adhesives use organic adhesives, and some use inorganic adhesives Agent, the two categories of organic solid core resistors and inorganic solid core resistors mentioned earlier are distinguished according to the type of adhesive. This type of resistor has strong overload resistance, high reliability, and is not easily damaged. If it is damaged, it will be in an open circuit state, that is, although the neon tube is not damaged, it will not light up, but the person holding the test pen to measure the live wire will not get an electric shock.
③The risk of electric shock occurs when the live wire originally has electricity but the test pen's resistor is damaged and falsely reports that there is no power. People can easily touch the live wire by mistake and get an electric shock!
If the resistance of the measuring pen (mostly solid suppressed resistors, with a resistance value of several M) is broken, there are two situations:
First, it is disconnected (this situation is common). After the resistance is disconnected, the electrical measuring circuit is disconnected, the neon bulb of the test pen has no current, and the neon bulb does not light up, which may easily cause misjudgment of the charged status of the circuit under test;
The second is a short circuit (this situation is rare). The neon tube of the electric test pen breaks down due to the high voltage it instantly withstands (the normal working voltage of the neon bulb is 70V). At this time, the neon tube acts as an insurance and will not cause harm to people.
