h EN or HD lists its deviations (see Figure 23.6). However, the telecom requirements in IEC 950 are not precisely the same as those in EN 41003, although they are very similar. A document showing a side by side comparison is Table 23.1 IEC standard and its EN equivalent available, and this is being used by the authors of both standards to eliminate unnecessary differences. The main differences are: IEC standard EN equivalent EN 41003 covers line-powered equipment. IEC 950 at present does not, although a proposal has been made to amend it so that IEC 950 EN 60950 it would. IEC 65 HD 195 56 The rules in EN 41003 for the maximum levels of ringing IEC 335 EN 60335 signals are based on IEC 479 and they match European telecom practice. IEC 950 permits an alternative set of rules based on IEC 1010 HD 401 S1 north American practice. Most analogue telephone equipment, IEC 601-1 EN 60601-1 it is believed, will satisfy both sets of rules. 3. The upper limit for the voltage of a telegraph signal is much higher in IEC 950 than in EN 41003 (135V peak vs. 96V peak) to cover existing practice in geographically large countries. from the IEC version. The corresponding standards are given in However the high levels permitted in both standards are con- Table 23.1. In a few CENELEC countries some additional require- sidered to be just as hazardous as mains voltage and must not ments are illegally imposed and CENELEC is endeavouring to be accessible to the user. enforce its rules to prevent this. Any of the equipment mentioned in Figure 23.4 may be connected Later in this chapter the requirements and tests in EN 41003 will to a telecommunication network but IT (Information Technology) be considered in more detail. equipment is the commonest. With one exception, none of these IEC or CENELEC standards contains requirements to meet objectives (2) and (3), which only concern equipment connected to a network. Classical safety standards Guide 105 shows in general terms how any IEC standard can be enhanced to cover (2) and (3) but being only