The terminal should be safe in chemical properties and structural materials, such as the edges and corners of plastic parts, burrs of metal materials, assembly density, and stability of products under conditions of movement, etc. All of these are the requirements of electrical relay equipment for the mechanical structure of terminals. The protection requirements of the enclosure are mainly the regulation of the protection level, the protection level of solid foreign bodies and the harm of water to equipment and products.

The insulating material, working voltage and environmental pollution grade of SP terminal are used to reasonably select the electrical gap and creepage distance, so that the product will not be damaged by over-voltage, so as to protect the safety of power relay equipment. Thermoplastic materials are required for deformation in work. It mainly affects the temperature rise of terminals and the high temperature caused by contact resistance, which softens the shell deformation and causes short circuit and serious accidents. Therefore, the conductive component material of terminals is also a key factor.

If a conductive path is formed on the surface of the solid insulating material under the action of electric field and electrolyte during the use of the terminal, the insulation performance of the shell insulating material will be reduced, which will affect the safety of the relay equipment. Therefore, the requirement of power relay equipment on the safety performance of terminal is very high, because industrial modernization needs more safety appliances.