Is it dangerous to have a broken measuring pen or a faulty measuring wire
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 at the M Ω level, and it is in series with the neon tube to limit current and avoid large current 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 fault such as poor contact between the resistor and the neon tube and spring, without knowing the fault, use the electric 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 may cause misjudgment and cause electric shock to the user. In addition, if the measuring pen accidentally enters water and is damp inside, 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.
The reliability of the simple test pen is not very high. When repairing AC220V lines, it is best to use the AC voltage range of a digital multimeter to measure AC high voltage.
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. The black probe should contact the ground or wall, and the red probe should contact 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, unlike measuring an electric pen, there will be current flowing through the human body, which is safer.
① It's very dangerous!
② However, the danger does not occur when measuring the live wire with a stylus. The high resistance resistors used in measuring pens are solid core resistors, also known as volumetric resistors, which are divided into two categories: organic synthetic solid core resistors and inorganic synthetic 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. 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, meaning that although the neon tube is not damaged but does not light up, the person holding the measuring pen to measure the fire wire will not be electrocuted
③ The danger of electric shock occurs when a person accidentally touches the live wire and gets an electric shock when the resistor of the measuring pen is damaged and the alarm is lost due to the original live wire being charged!
If the resistance of the measuring pen (mostly solid suppression resistance, with a resistance value of several M) is broken, it can be divided into two situations:
One is disconnection (which 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 the neon bubble does not light, 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 momentary 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.
