Some aspects of protection of telephone subscriber line against contact with the mains

The telephone lines and the devices connected to them in a real environment are exposed to overvoltage and overcurrent disturbances. The requirements placed upon protective circuits differ in view of the variety of such disturbances, and the solutions are compromises. The segment of overcurrent protection has to be paid the highest attention since it is vital for the safety of people and devices. The article presents the results of measurement and an overall analysis of resistor networks (fuses) as a component part of overcurrent protection. Stress is laid on possible hidden dangers that may originate in the difference in technologies used in the manufacture of resistor networks.