I wasn't involved with the development of the surge requirements for 10m cables but not shorter, but I do remember some of the rational:
Compared to other phenomena in EMC, surges are relatively slow and consist of energy at primarily at frequencies of a few MHz, as opposed to hundreds of MHz or even GHz for EFT and/or ESD events. As a result, pick-up of radiated energy at these low frequencies by short cables is minimal and not considered to be a problem; however, as the cables get longer, it gets more and more likely that significant energies can be induced into cables from slow surge events, such as distant lightning or other switching transients. Whether the cable is inside or outside doesn't matter: very long cables inside a high rise building are just as an effective at picking up energy from nearby lightning as telephone lines strung horizontally outside a building. As a side note, there used to be an old lineman's rule of thumb: 1kV per meter per mile -- In other words, it is possible to develop 1kV across a meter of unterminated wire a mile from the flash. I have no idea how accurate this is, but it was commonly used in the 60's and 70's. Anyway -- the basic idea is that shorter cables won't pick-up any significant energy from a radiated surge event. Hope this helps, Mike Hopkins -----Original Message----- From: Zohar Zosmanovich [mailto:[email protected]] Sent: Wednesday, December 20, 2000 6:47 AM To: '[email protected]' Subject: Surge (immunity) requirement for equipment in telecommunication c enters Hi, The EN 300 386 (EMC requirements for telecommunication network equipment) require to perform a surge of 1.2/50 Tr/Th us, 0,5 kV to ports for indoor signal lines (in telecommunication centers), when cables longer than 10 m are connected ! Can some one explain my the rational of divided up to 10 m and more than 10 m, anyway all cable is in the building (indoors) ? Zohar (Jana) Zosmanovich Compliance Engineer, RADWIN ltd. 34 Habarzel St., Tel Aviv 69710, Israel Tel.: 972-3-7666735 ; Fax: 972-3-7657535 Email: <mailto:[email protected]> ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected] ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
