Leakage protector, referred to as leakage switch, also known as leakage circuit breaker, is mainly used in the equipment leakage failure and fatal danger of personal shock protection, with overload and short circuit protection function, can be used to protect the line or motor overload and short circuit, can also be used under normal circumstances as the line of the infrequent conversion start.
Leakage protector can be classified according to its protection function, structural characteristics, installation mode, operation mode, pole number and line number, action sensitivity and so on. Here, it is mainly described according to its protection function and use classification. Generally, it can be divided into three kinds: leakage protection relay, leakage protection switch and leakage protection socket.
1. Leakage protection relay refers to the leakage protection device which has the function of detecting and judging the leakage current, but does not have the function of cutting off and connecting the main circuit. The leakage protection relay is composed of zero sequence transformer, tripping device and auxiliary contact of output signal. It can be used as the total protection of low-voltage power grid or the monitoring protection of leakage, grounding or insulation of the main circuit.
When there is leakage current in the main loop, because the auxiliary contact and the separation trip device of the main loop switch are connected in series into a primary circuit, so the auxiliary contact connects the separation trip device and disconnects the air switch, AC contactor, etc., so that it is off and the main loop is cut off. Auxiliary contacts can also be connected to the acoustic and optical signal device, leakage alarm signal, reflecting the insulation status of the line.
2. Leakage protection switch refers to not only it and other circuit breakers can be switched on or off the main circuit, and has the function of leakage current detection and judgment, when there is leakage or insulation damage in the main circuit, leakage protection switch can be switched on or off the main circuit according to the judgment result of the switch element. It can be combined with fuses and thermal relays to form a fully functional low-voltage switching element.
At present, this form of leakage protection device is the most widely used. The leakage protection switches on the market are commonly used in the following categories according to their functions:
(1) Only with leakage protection power off function, must be used with fuse, thermal relay, overcurrent relay and other protective components.
(2) It also has overload protection function.
(3) with overload, short circuit protection function.
(4) At the same time with short circuit protection function.
(5) At the same time with short circuit, overload, leakage, overvoltage, undervoltage function.
3 leakage protection socket refers to the power socket with leakage current detection and judgment and can cut off the circuit. Its rated current is generally below 20A, leakage action current 6 ~ 30mA, high sensitivity, often used for handheld electric tools and mobile electrical equipment protection and home, school and other civil places.
Since the invention and use of electricity, electricity can not only bring a lot of convenience to human beings, but also bring the ultimate disaster to human beings. It can burn out appliances, cause a fire, or electrocute people. If there is a device that enables people to use electricity safely, a lot of unnecessary losses will be avoided. So in a variety of electrical appliances one after another, but also the birth of a variety of protectors. One of them is specifically designed to protect people, called the leakage protector. Leakage protector, commonly known as leakage switch, is used to prevent personal shock and electrical fire protection when the circuit or electrical insulation is damaged short circuit to the ground. It is generally installed in the socket circuit of each household distribution box and the power supply line of the whole building distribution box, the latter is dedicated to prevent electrical fire.
The leakage protector has experienced a long development process and is now widely used all over the world. 
In 1930 in Europe invented the voltage action leakage protector, used to prevent electrical equipment due to insulation damage caused by electric shock accident. The current - operated leakage protector was introduced in 1960. At present, the voltage action type leakage protector has been eliminated in the world, and the current action type leakage protector has become the main electrical device for leakage and shock protection.
In 1964, Japan began to develop the voltage action type leakage protector to prevent electric shock accidents in the construction site. In 1966, it introduced the electromagnetic current action type leakage protector from West Germany. In 1976, it began to produce the integrated circuit leakage protector.
The United States has used the current action type leakage protector since 1967. Due to the electric shock accident in the swimming pool, the development of the leakage protector has been attached importance, and the use of the leakage action current of 5mA leakage protector has been required at the very beginning.
In our country, the voltage action type leakage protector was developed in 1966, the electromagnetic leakage protector was developed and produced in 1976, and the integrated circuit leakage protector was developed and produced in about 1985.
The popularization and application of leakage protector is inseparable from the formulation of standards and regulations. The 1971 edition of the National Electrical Code (NEC) in the U.S., stipulates that from January 1, 1973, it is mandatory to install leakage protection devices in homes and construction sites. Japan's "Technical Standards for Electrical Equipment" and the Ministry of Labor's "Safety and health rules" stipulate that the electrical equipment with working voltage over 60V must be set up in wet places, and the leakage protector must be set up in all 400V circuits.
In the Decision on strengthening the work of Labor Protection made by the State Administration of Construction in 1981, the electric equipment in construction site must be set up with leakage protection devices. It is stipulated in GB3787-1983 "Safety Technical Regulations for the Management, Use, Inspection and Maintenance of Hand-held Electric Tools" that hand-held electric tools must use leakage protectors. It is stipulated in JGJ46-1988 "Technical Specifications for Safety of Temporary Electricity Use in Construction Site" formulated by the Ministry of Construction in 1988. Electric construction machinery and hand-held electric tools must be equipped with leakage protection devices, and it is required to implement secondary leakage protection, including leakage protection of the main power supply, in the construction site.