IEC 61643-21:2000+A1:2008 is applicable to devices for surge protection of telecommunications and signalling networks against indirect and direct effects of lightning or other transient overvoltages. The purpose of these SPDs is to protect modern electronic equipment connected to telecommunications and signalling networks with nominal system voltags up to 1 000 V (r.m.s.) a.c. and 1 500 V d.c. The contents of the corrigendum of March 2001 have been included in this copy. This consolidated version consists of the first edition (2000) and its amendment 1 (2008). Therefore, no need to order amendment in addition to this publication.