New IEC 61643-21 - Improvements of safety-related requirements for SPDs in telecommunication and signalling networks

Since energies for supplying sensors are transmitted on the same line as the data, it is necessary for the standard for surge protective devices (SPDs) in telecommunication and signalling networks to cover this situation. SPDs for the pro-tection of the sensitive electronic equipment of telecommunication and signalling networks are qualified according to IEC 61643-21. This international standard is currently being adapted to these circumstances. The new Edition is called: IEC 61643-21 Edition 2 "Low voltage surge protective devices - Part 21: Surge protective devices connected to tele-communications and signalling networks - Requirements and test methods". This paper describes which additional safe-ty-relevant requirements and changes are requested and integrated into this standard and technical backgrounds are ex-plained. Additionally, the introduced test procedures especially the safety relevant tests for SPDs with UC times IL > 100 W, where UC is the maximum continuous operating voltage and IL is the rated load current, are shown in practical application. The results presented show how the combination of a backup fuse coordinated to an integrated disconnec-tion method can transfer aged or overloaded SPDs into a safe behaviour even in case of application in signalling net-works with higher system voltages and/or a high short-circuit capability.