Just as electricity has been widely used in human life, the temporary connection of equipment in industry has also been widely used. NEMA wiring device must be as small as possible in order to realize frequent commutation, but also to realize braking during commutation and acceleration after commutation. Therefore, it is necessary to adopt commutation device quickly and braking device effectively. IP54, that is, dust prevention is level 5: dust intrusion cannot be completely prevented, but the amount of dust intrusion will not affect the normal operation of the product; Waterproof grade 4: prevent splashing water from invading, and prevent splashing water from all directions from invading. Industrial plugs are suitable for industry, generally divided into 3-core, 4-core, 5-core, etc. The current is generally divided into 16A, 32A, 63A, 125A, 250A, 420A, etc., and the protection level can be divided into IP44 and IP67, which are relatively conventional. Generally, it is used with industrial sockets and industrial connectors. This kind of temporary connection is usually industrial plug and socket connection, and there are two connection modes, one is brass pin sleeve type, and the other is point contact type socket.The following will describe the evolution of industrial plugs.I. Brass pins and sleevesIn the 19th century, the design of copper pin and bushing contact plug and socket is still in use today, just like what we used in the market, the connection technology is not much different from that designed at that time, so we haven't changed? Of course, the voltage, current, frequency and the number of people involved in the connection operation have greatly increased.Since the Second World War, in order to be compatible with products from different manufacturers, a standard size CEE17 has been formulated, which makes it very convenient to connect other electrical equipment. It is also because this standard has caused the contact technology of industrial plugs and sockets to stand still. Of course, the design of cylindrical pins and contact sleeves is one of the economic uses in manufacturing industrial plugs and sockets. However, with the continuous improvement of people's living standards, the requirements for products are also increasing, and with the increase of voltage and current, this design has its limitations.Only from the design point of view, brass pins and bushing contacts are not suitable for breaking under load, because the material (brass) used in the production of such products is not resistant to electric arc. Because under the action of electric arc, brass will produce high-resistance oxide, which will increase the contact resistance of plug and socket and raise the temperature. Temperature rise further increases the oxidation and contact resistance of contact points, and the increase of contact resistance will reduce the working performance of plugs and sockets. Although we don't want the above phenomena to occur, in practical use, we should avoid electric arc.2. Problems between products of different manufacturersWhen the plug is inserted into the socket, the conductivity requires at least one contact surface. In the traditional pin and sleeve design, the force on the contact point is realized by the spring of the cotter pin or sleeve, or by the spring stretching around the sleeve. But for economic reasons, the size of the spring is not too high, which makes it impossible to accurately control the minimum applied force when you plug the products of one manufacturer into the socket of another manufacturer. They will feel that manual operation is inconvenient, and their contact resistance will be different due to manufacturing tolerances, which can not guarantee the stable performance of products in use.III. Importance of accurate toleranceBecause of the high mobility of industrial plugs and sockets, they are often connected with different devices. When one batch of mechanical parts is transferred to another, it is impossible to maintain accurate dimensions.