Power and postal communication system audio-frequency line distribution cabinet (frame) security unit
　　 The security unit adopts pressure sensitive circuit, thermal melting block and polyswitch. The work principle of the security unit: when some communication lines are under thunder attack or in contact with power lines, the air discharge tube will discharge (or the pressure sensitive resistor will limit) to bring the dangerous voltage to within the safety limit. If the lines are under the current of over 350mA for a long time, the resistance of PTC will increase any time to make high resistance for the electrical circuit and the current of the loop will reduce, protecting the exchange equipment. When the higher current disappears, PTC will restore to its original condition immediately.
　　 Our company has manufactured clip type and wiring connection type distribution frame (cabinet) according to the characteristics of the power supply and postal systems, and this product is now in wide use in power supply, postal service and air defense and many other sectors. We also supply imported thunder arresters: OBO of Germany, FURSE of the U.K., ESP of France, etc., which can be used in power supply, signal devices and computer network for protection against thunder.