What will happen if the test pen breaks and the test wire
When using a digital multimeter instead of a measuring probe to determine the neutral and live wires, the range switch can be adjusted to AC 200V voltage. The black probe should be in contact with the ground or wall, and the red probe should be in contact with two wires respectively. If the red probe is in contact with the neutral wire, the voltage displayed on the multimeter is very small, close to 0 volts. If the red probe is in contact with the live wire, the voltage displayed on the multimeter is generally above tens of volts. Using this method to measure AC high voltage is safer than using a measuring pen, as it does not allow current to flow through the human body.
① Very dangerous!
② However, danger does not occur when measuring the live wire with a measuring pen. The high resistance resistors used in measuring pens are solid core resistors, also known as volume 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 three substances: granular conductive material, non-conductive powder material used as filler, and adhesive. The granular conductive material consists of 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 show 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 there is electricity on the live wire, but the resistor of the measuring pen is damaged and falsely reports that there is no electricity. It is easy for people to accidentally touch the live wire and get an electric shock!
If the resistance of the measuring pen (usually a solid pressed resistor with a resistance value of several meters) is broken, it can be divided into two situations:
One is disconnection (which is common). After the resistor is disconnected, the measuring circuit is disconnected, and the neon bulb of the measuring pen has no current and does not light up, which can easily cause misjudgment of the charged state of the tested circuit;
The second is a short circuit (which is rare), where the neon tube of the measuring pen breaks down due to momentary high voltage (the normal working voltage of neon bubbles is 70V). At this time, the neon tube plays a safety role and will not cause harm to people.
[Note] The voltage of the tested circuit is usually 220V
