In a message dated 96-08-01, Debbie Mallory Olson writes: >By the way, can someone help educate me on the K.21 requirement for >lightning surge for TE? Why have most European countries dropped this, >but Switzerland, the Czech Republic, and Italy still require it? Section >9 a) says "TE that employs insulation spacings that are dimensioned and >tested in accordance with IEC 950 need not be subjected to further tests >under this Recommendation". Does this mean that my EN60950 approval is >adequate?
Debbie: EN 60950 is concerned only with product safety. The lightning requirements that appear in Switzerland, The Czech Republic, and Italy are performance requirements. The equipment must continue to function after the surges are applied. Thus, there is a fundamental difference in the motivation for applying the tests. For this reason, I would not expect these countries to consider compliance with EN 60950 as sufficient. In response to your question "why have most European countries dropped this?," I would say that to my knowledge, most European countries never had requirements to survive simulated lighting. During the last 10 years, the three countries that you mention are the only ones where I have encountered lightning immunity requirements (plus South Africa, of course). In general, the lightning environment in Europe is less severe than it is in the southeastern USA. Florida has been described as the "lightning capital of the world." This may help to explain why lightning immunity has not received as much attention in Europe. In response to your request for suggested test labs, you might try the Global Product Compliance Laboratory in Holmdel, NJ (908-834-1800). They have a very nice $50K Keytek surge generator that I have used for some Bellcore surges. Simulating the K.21 surge would be a simple matter if they have the proper plug-in module for K.21. Before you go to the trouble of testing, though, take a close look at the K.21 surge circuit. Yes, the voltages are high, but the source impedance is high too. For the 1500 volt surge, the short circuit current is only about 40 amps. Overall, I consider the K.21 surges to be less severe than the FCC Part 68 surges. Lastly, you questioned the remark in K.21 that "the test voltage may be different in different countries to meet local requirements." I believe that this is a reference to the fact that some countries use primary protectors that differ from the 1500 volt primary protector assumed in K.21, and some countries do not install primary protectors at all. In such cases, the test voltages might need to be revised. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc.
