ontinuing need to keep EN 41003 in existence. For one reason, other standards are beginning to refer to it, and a 23.6.6 Voltages from the network standard that is referred to by another standard cannot be with- drawn. Secondly, as explained earlier, EN 41003 can be used with Unwanted voltages may arrive from the network due to lightning equipment designed to another of the classical safety standards. strikes, cross contact between overhead power and telephone lines, and other interference. While there are very few cases of injury to telephone users from such causes, 4.5 of the standard does require separation of the line terminals from various parts of the equipment. 23.7 Choice of relevant safety As well as avoiding discomfort and possible injury to the user, such requirements separation is probably desirable for protection of any electronic circuits in the equipment. The separation is tested either with 10 All of EN 41003 applies where the equipment has an interface to the impulses or with a steady state voltage for 60 seconds. The manu- PSTN, because it was written around that system. However, not all facturer has the choice. It is not forbidden to have surge suppressors of it applies to every piece of telecom equipment. Subclause 4.4.2 connected to line (as in Figure 23.15 of this chapter) but special test and 4.5 may not apply; in some cases none of it applies. It is not conditions apply if this is done. IEC 950 is not quite the same always obvious to a hardware designer which parts do apply to the regarding these test conditions. box he is designing. The problem does not arise with traditional IT The use of impulse testing is to be preferred when surge sup- equipment: if a circuit needs to be accessible it needs to be an SELV pressors are used; the 60 seconds test may destroy them. It is also circuit or a limited current circuit, as specified in IEC 950; if a box best to leave them in place during impulse testing, otherwise the contains no cathode ray tube, the section on cathode ray tubes parts they are t