The leakage protection switch mainly provides indirect contact protection. Under certain conditions, it can also be used as a supplementary protection for direct contact to protect against potentially fatal electric shock accidents.
When a person is electrocuted, the greater the current flowing into the human body and the longer the phase current lasts, the more dangerous it is. The degree of danger can be roughly divided into three stages: perception-escape-ventricular fibrillation.
① Perception stage: Since the current flowing into the human body is very small, the human body can feel it (generally greater than 0.5mA), which does not pose a hazard to people at this time;
② Escape stage: refers to the maximum current value that a person can escape when holding the electrode for electric shock (generally greater than 10mA). Although this current is dangerous, it can be escaped by oneself, so it basically does not constitute a fatal danger. When the current increases to a certain extent, the person who is electrocuted will contract his muscles and have spasms, causing him to grasp the charged body and cannot escape by himself.
③ Ventricular fibrillation stage: As the current increases and the duration of electric shock increases (generally greater than 50mA and 1s), ventricular fibrillation will occur. If the power supply is not disconnected immediately, it will lead to death.
It can be seen from this that ventricular fibrillation is the main cause of death from electric shock. Therefore, for human protection, not causing ventricular fibrillation is often used as the basis for determining the electric shock protection characteristics.
What is the safety of "30mA·s"?
A large number of animal experiments and studies have shown that the induction of ventricular fibrillation is not only related to the current (I) passing through the human body, but also to the duration of the current in the human body (t), that is, it is determined by the safe amount of electricity passing through the human body Q=I×t, which is generally 50mA·s.
That is to say, when the current is not greater than 50mA and the current duration is within 1s, ventricular fibrillation generally does not occur. However, if controlled according to 50mA·s, when the power-on time is very short and the current is large (for example, 500mA×0.1s), there is still a risk of inducing ventricular fibrillation.
Practice has proved that using 30 mA·s as the action characteristic of the electric shock protection device is more suitable in terms of safety of use and manufacturing, and has a safety rate of 1.67 times that of 50 mA·s (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 protection switch operates within 0.3s and cuts off the power supply, the human body will not cause fatal danger. Therefore, the limit of 30mA·s has also become the basis for the selection of leakage protection switch products.