In a message dated 6/13/2003, Jeffrey Collins writes:
( 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? Hi Jeffrey: I think the exemption for cables that are shielded and grounded at both ends is based on the *assumption* that this form of shielding will prevent significant energy from being coupled onto the twisted wire pairs. If you decide to perform the tests by actually applying the specified surges to the twisted pairs, I don't think the presence of a shield and/or ground will make any difference in the results. In general, I have found that it is fairly easy to design T1, E1, and Ethernet ports to pass these tests. However, if consideration of these surges was not part of the original design, there is usually something that will cause the port to fail. For example, the spacings or trace widths in the layout may be inadequate, a needed surge protector may be missing, or the chosen magnetics may be inappropriate. Lightning tolerant designs often have some differences on the low voltage side of the barrier as well. In view of this, don't be too surprised if your interfaces fail the tests. In fact, some types of failure can be predicted by an inspection of the schematic and the layout. You might want to review these before you start testing, just to get an idea of what the likely outcome will be. By the way, you have included RS-232 in your list of ports that are subject to these tests. I do not normally classify RS-232 as a "telecommunication port" for the purposes of these tests. Maybe this determination is subject to different interpretations. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 [email protected] http://www.randolph-telecom.com
