Experience in the operation of telecommunication centres shows that the use of a bonding and earthing network that is coordinated with equipment capability and with electrical protection devices@ has the following attributes: - promotes personnel safety and reduces fire hazards; - enables signalling with earth return; - minimizes service interruptions and equipment damage; - minimizes radiated and conducted electromagnetic emissions; - reduces radiated and conducted electromagnetic susceptibility; - improves system tolerance to discharge of electrostatic energy@ and lightning interference. Within this framework@ this Recommendation: a) is a guide to bonding and earthing of telecommunication equipment in telephone exchanges and similar telecommunication switching centres; b) is intended to comply with safety requirements imposed by IEC [2] or national standardizing bodies on a.c. power installations; c) can be used for installation of new telecommunication centres@ and@ if possible@ for expansion and replacement of systems in existing centres; d) treats coordination with external lightning protection@ but does not provide details of protective measures specific to telecommunication buildings; e) addresses the shielding contribution of the effective elements of the building; f) addresses shielding provided by cabinets@ cable trays and cable shields; g) is intended to encourage EMC planning@ which should include bonding and earthing arrangements that accommodate installation tests and routine diagnostics; h) does not include: - required values of surge current immunity and insulation withstand voltages; - limits of radiated and conducted electromagnetic emission or immunity; - techniques for verifying and maintaining bonding and earthing networks.