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Questions About Earth Leakage Circuit Breaker(ELCB)

Questions About Earth Leakage Circuit Breaker(ELCB)

  • Monday, 25 December 2023
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An Earth Leakage Circuit Breaker(ELCB), also known as a Residual Current Device (RCD)Earth Leakage Protector(ELP), is an electrical safety device used to protect against electric shocks and electrical fires.


Q1: What are the main technical parameters of leakage protectors?

Answer: The main performance parameters include: rated leakage current, rated leakage time, and rated

leakage current without action. Other parameters include: power frequency, rated voltage, rated current, etc.

① The rated leakage current is the current value at which the leakage protector operates under specified conditions. For example, a 30mA protector will disconnect the power supply when the current value reaches 30mA.

② The rated leakage action time refers to the time from the sudden application of the rated leakage action current until the protective circuit is cut off. For example, 30mA × The time from the current value reaching 30mA to the separation of the main contact of the 0.1s protector shall not exceed 0.1s.


Q2:What is the main protective function of a leakage protector?

Answer: Leakage protectors mainly provide indirect contact protection, and under certain conditions, they can also be used as supplementary protection for direct contact to protect against potentially fatal electric shock accidents.


Q3. What are direct and indirect contact protection?

Answer: When the human body comes into contact with a charged object and there is an electric current passing through the human body, it is called electric shock to the human body. According to the causes of electric shock in the human body, it can be divided into direct electric shock and indirect electric shock. Direct electric shock refers to the electric shock caused by the human body directly touching a charged object (such as touching a phase line). Indirect electric shock refers to the electric shock caused by the human body touching a metal conductor that is not normally charged but is charged under fault conditions (such as touching the outer shell of a leakage device). According to the different causes of electric shock, the measures taken to prevent electric shock are also divided into direct contact protection, phase to phase contact protection. Direct contact protection can generally adopt measures such as insulation, protective covers, fences, and safety distances; Indirect contact protection can generally adopt measures such as protective grounding (zero connection), protective cut-off, and leakage protection devices.


Q4. What is the safety of "30mA · s"?

Answer: Through a large number of animal experiments and studies, it has been shown that the cause of ventricular fibrillation is not only related to the current passing through the human body (I), but also to the duration of the current in the human body (t), that is, the safe electric quantity passing through the human body Q=I × To determine, it is generally 50mA · s. That is to say, when the current is not greater than 50mA and the duration of the current is within ls, ventricular fibrillation generally does not occur. However, if controlled according to 50mA · s, when the power on time is short and the human current is high (e.g. 500mA) × 0.1s), there is still a risk of triggering ventricular fibrillation. Although electrocution below 50mA · s does not result in fatal consequences, it can also cause the electrocuted person to lose consciousness or cause secondary injury accidents. Practice has proven that using 30 mA · s as the operating characteristic of the electric shock protection device is more suitable in terms of both safety and manufacturing. Compared with 50 mA · s, it has a safety rate of 1.67 times (K=50/30=1.67). From the safety limit of "30mA · s", it can be seen that even if the current reaches 100mA, as long as the leakage protector operates and cuts off the power supply within 0.3s, there is still no fatal danger to the human body. Therefore, the limit of 30mA · s has also become the basis for the selection of leakage protection devices.


Q5.What are the dangers of electric shock in the human body?

Answer: When the human body is electrocuted, the greater the current flowing into the body, the longer the duration of the phase current, the more dangerous it becomes. The degree of danger can be roughly divided into three stages: perception escape ventricular fibrillation Perception stage. Due to the small amount of incoming current, the human body can feel it (generally greater than 0.5mA), which does not pose a danger to humans; ② Get rid of the stage. The current value (usually greater than 10mA) that a person can get rid of when holding an electrode and getting an electric shock. Although this current is somewhat dangerous, it can be overcome on its own, so it does not constitute a fatal danger. When the current increases to a certain extent, the person who is electrocuted will experience muscle contractions and spasms, causing them to grip the charged body tightly and cannot get rid of it on their own Stage of ventricular fibrillation. As the current increases and the duration of electric shock prolongs (generally greater than 50mA and ls), ventricular fibrillation will occur. If the power is not immediately disconnected, it will lead to death. From this, it can be seen that ventricular fibrillation is the main cause of electrocution death in the human body. Therefore, the protection of humans is often based on not causing ventricular fibrillation as a basis for determining the characteristics of electric shock protection.


 

笔记



③ Under specified conditions, the rated leakage current at which the leakage protector does not operate should generally be half of the leakage current value. For example, a leakage protector with a leakage current of 30mA should not operate when the current value reaches below 15mA, otherwise it is prone to misoperation due to high sensitivity, which affects the normal operation of electrical equipment Other parameters such as power frequency, rated voltage, rated current, etc. should be suitable for the circuit and electrical equipment used when selecting a leakage protector. The working voltage of the leakage protector should adapt to the normal fluctuation range of the power grid and the rated voltage. If the fluctuation is too large, it will affect the normal operation of the protector, especially for electronic products. When the power supply voltage is lower than the rated working voltage of the protector, it will refuse to operate. The rated working current of the leakage protector should also be consistent with the actual current in the circuit. If the actual working current is greater than the rated current of the protector, it can cause overload and cause the protector to malfunction.


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