In the process of using electrical appliances, sometimes used to touch the shell will have a feeling of numbness, testing the neon lamp with an electric pen will emit light, which is the phenomenon of leakage that people often encounter.
But why does this happen?In real life, there are many reasons why people encounter electricity leakage.
Analysis of leakage causes: leakage is usually the mains current phase line, also known as the fire line and the housing of home appliances, including some exposed parts, there is one or more current leakage paths. According to the different current leakage paths, there are mainly the following three types:
1, short circuit leakage
Refers to the direct communication between the mains phase line, including motors and transformers connected with phase line, and the housing of home appliances due to serious aging and damage.This kind of leakage is very dangerous and could endanger the lives of people who get electrocuted.
2. High resistance leakage
Insulation resistance exists between the housing of the appliance and the mains phase line.Even the best insulation material is not absolute insulation.But the resistance value is very large, so no matter what kind of household appliances, usually have an insulation performance refers to ensure that household appliances leakage will not harm people and objects.Refrigerators, for example, have insulation resistance of no less than 2MQ.It has been designed so that the insulation resistance is very high that the leakage current is extremely weak.It's not normally felt by the human body.But if the insulation resistance drops in damp conditions or over time, the leakage may be felt by touching the housing.
3. Capacitive leakage
There is a certain amount of capacitive ac between the mains phase line and the housing of home appliances.A distributed capacitance formed by the windings of an electric motor in a washing machine in relation to metal parts such as the rotor or stator.Because of this leakage of electrical capacity is not generally tens to hundreds of micromethods for 50Hz city power capacitive reactance is very large.
Small leakage currents have little impact on human safety.Of course if it's a capacitor that breaks down or leaks a lot it's a different situation and then it turns into a short-circuit leakage.In real life, there will also be leakage or induction caused by high-voltage several kilovolts to tens of thousands of volts, such as television, especially color television picture tube anode high voltage through a variety of leakage and static electric field induction and make the housing or picture tube screen electrified.The voltage of this leakage may be high but the energy is small.Won't cause electrocution to die accident commonly, but can cause certain burn.
Judgment of leakage property
For leakage below 220V, set the multimeter to ac 250V or 500V transmission.One meter pen connected to the housing or exposed live components, the other meter pen connected to the zero line, the general will appear 100 to 220V voltage reading.This reading is related to leakage current and internal resistance of multimeter.Then dial down the range of the multimeter step by step and observe the pointer change.If with the range dial small, the indicator value or deflection Angle proportional to a large increase, or even in the range of 100V below the range are all over the range, it means that it is short-circuit leakage, if with the range dial small, the indicator value slightly increased, the deflection Angle of the pointer is very small, it is high resistance or capacitance leakage.Neon lights glow when a stylus touches an insulating housing or a picture tube screen, even in high voltage system space, where electric fields are applied.This kind of leakage is high voltage leakage.