What will happen if the test pen is broken and the fire detection wire is broken
The internal part of the measuring pen is generally composed of high resistance resistors, neon tubes, and springs. The resistance value of this high resistance resistor is generally in the M Ω level, and it is in series with the neon tube to limit the current and prevent large currents from flowing through the neon tube and the human body during testing. The possibility of damage to the resistor is very small, but if there is a poor contact between the resistor and the neon tube and spring, and it is not known that there is a fault, use this pen to measure whether the charged body has AC high voltage. At this time, the neon tube will not light up (or the brightness is weak), which will cause misjudgment and cause the user to be electrocuted. In addition, if the inside of the measuring pen has accidentally entered water and is damp, using this pen to measure the AC220V voltage can also easily cause electric shock accidents. Therefore, before using the measuring pen, it is necessary to check its condition and confirm that there are no faults before using it.
When using a digital multimeter instead of a measuring pen to determine the zero and live wires, the range switch can be set to the AC 200V voltage range, with the black probe touching the ground or wall and the red probe touching two wires respectively. If the red probe contacts the zero wire, the voltage displayed on the multimeter is very small, close to 0V. If the red probe contacts the live wire, the voltage displayed on the multimeter is generally tens of volts or more. Using this method to measure AC high voltage is safer as there is no current flowing through the human body like using a measuring pen.
① Very dangerous!
② However, the danger does not occur when using a stylus to measure the live wire. The high resistance resistors used in measuring pens are solid core resistors, also known as volumetric resistors, which are divided into two categories: organic composite solid core resistors and inorganic composite solid core resistors. This type of resistor is made by mixing and pressing granular conductive materials, non-conductive powder materials used as fillers, and adhesives. Granular conductive materials are carbon black and graphite; Non conductive powder materials include mica powder, quartz powder, glass powder, titanium dioxide powder (titanium dioxide powder), etc; Some adhesives use organic adhesives, while others use inorganic adhesives. The two categories of organic solid core resistors and inorganic solid core resistors mentioned earlier are distinguished based on the type of adhesive used. This type of resistor has strong overload resistance, high reliability, and is not easily damaged. If it is damaged, it will also be in an open circuit state, which means that although the neon tube is not damaged but does not light up, the person holding the measuring pen to measure the live wire will not be electrocuted.
③ The danger of electric shock occurs when a person is prone to accidentally touching the live wire and getting an electric shock due to a damaged resistor in the test pen, which could result in a false alarm of no power!
Measure the resistance of the electric pen (mostly solid suppression resistance, with a resistance value of several meters). If it is broken, it can be divided into two situations:
One is disconnection (this situation is more common). After the resistance is disconnected, the measuring circuit is disconnected, and the neon bubble of the measuring pen has no current and does not light up, which can easily cause misjudgment of the electrification of the tested circuit;
The second is a short circuit (this situation is rare), and the neon tube of the measuring pen breaks down due to instantaneous high voltage (the normal working voltage of the neon bubble is 70V). At this time, the neon tube plays a safety role and will not cause harm to people.
