Jeff, I think the difference may be in the distributed ground arrangement in the CBN. In a surge event, the CBN would distribute the energy from a lightning event and common mode voltage differences within the CBN would minimal (hence the exemption).
In an IBN (shielded w/isolated ground), the differences in ground potentials could be severe and the test would be necessary. Unshielded cables could obtain coupled energy from the building (the classic intrabuilding example) and also make the test necessary. Since most if not all North American telecom providers (those that use the NEBS standards) do NOT want to install IBN equipment, you should be able to stick with your shielded cable exemption if you want to. If EMI considerations aren't an issue and you want to test for the unshielded intrabuilding, I'd go for it because I have always had the impression that carriers don't like to run STP (cost & labor objections if nothing else). BTW, about a year ago I looked into the floating one end of the shield thing (well, for coaxial DS3/E3 anyway) and found out that no one requires isolation any more. There were a few countries that held out longer than others but the isolation is no longer required anywhere in the world (I think the EMC issues outweighed the ground loop problem). Anyone out there feel free to correct me if I'm wrong, but I spent quite a bit of time researching this. Best Regards, Dave Heald >>> "Collins, Jeffrey" <[email protected]> 06/13/03 08:07AM >>> All, We have taken the waiver to this requirement by using shielded cables that were grounded on both ends. Since it is common for carriers to float one end of their grounds we are planning to perform this test on our telecom ports. Looking at the levels of the surge in table 4-4, I'm not confident that a grounded shielded telcom cable would make the difference in passing this test. ( Surges are at 800V and 1500V) ( Ports / Cables are T1, E1, Ethernet, and RS232) My plan is to run this test with both unshielded ungrounded cables and shielded grounded cables. Does anyone have any experience in passing this test where the shielded/grounded cable made the difference? Anyone have a theoretical opinion/prediction on this? Thanks in advance, Jeffrey Collins Sr. HW Engineering Manager EMC/ NEBS/ Reliability/ Safety CIENA Corporation 5965 Silver Creek Valley Rd. San Jose, CA. 95138 (408) 571-3002, Fax (408) 965-2705 [email protected] http://www.ciena.com This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ________________________________________________________________________ This email has been scanned for computer viruses. ________________________________________________________________________ This email has been scanned for computer viruses. This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
