 in technical requirements in the next few years. The word 'safety' is used in the meaning of the avoidance of injury to persons, either those using the equipment or (in telecommunica- 3. Safety of the equipment user from voltages on a network (see tions applications) those working on the line or at the other end of Figure 23.3). it. Protection, meaning the avoidance of damage to equipment hardware, is not covered, although many design features for safety Lightning purposes will provide some protection. Extensive reference is made to EN 41003, this being the only standard dealing only with telecom safety as currently conceived. The reader is advised to obtain copies of EN 41003 and of IEC 950, second edition, and to study the Principles of Safety in the latter. Apparatus Network Figure 23.3 Safety of the user from network voltages The 'network' in mind when this Guide was written (1984-1985) Mains supply was the PSTN, Public Switched Telephone Network. The first of these objectives has nothing to do with the telecom network and is the subject of the classical safety standards which exist for most electrical products. Figure 23.4 shows some of the Figure 23.1 Safety of the user from electrical hazards in international (IEC) standards for such products. Similar or identical the equipment national standards exist in many countries including Australia, Canada and USA. 23/4 Safety and EMC Radio, Domestic Measuring Electro- equipment TV, Hifi appliances equipment medical Figure 23.4 Classical product safety standards In Europe there is a European version of each one (a European classical standard may be the IEC standard as shown, or the national Norme, EN, or Harmonization Document, HD) which is substan- or European version of it. tially identical to the corresponding IEC standard and which in the In one case, the telecom requirements have been included in the case of an EN has to be adopted as the national standard by all classical standard, namely in the 1991 second edition of IEC 950 member countries of CENELEC. Eac