In a message dated 4/17/2003, you write:
As an FYI, we see very few instances of damage on our carrier class products due to lightning events. As such I doubt the coordination issue is really that significant. Hi Jim: Thanks for your detailed discussion of the coordination problem. I share the concerns you expressed, particularly your general discomfort with the surge tolerance of PTC devices. I should also mention that my own experience is that GR-1089 compliant products rarely have lightning failures in the field. I have seen some cases where the *voltage* of real world longitudinal lightning surges exceeded what GR-1089 tests for, due to nonfunctional primary protectors. GR-1089 makes no attempt to treat this field condition as a Level 1 test, but experience has taught me that it must be considered. On the other hand, I have not seen any significant incidence of cases where the short circuit *current* was enough to damage a GR-1089 compliant design. Fuses that can handle a 10x1000 uS, 100 amp surge almost never fail in the field. This suggests to me that the coordination requirement in the new K.20 is excessive, and that the coordination requirement in GR-1089 is probably more closely aligned with actual field conditions. GR-1089 does not require the primary protector to operate if the secondary protector can handle 10x1000 uS 100 amp surges. I wonder whether there is any room for the authors of K.20 to consider lowering the amount of short circuit current that the secondary protection must be able to survive in order to waive the requirement that the primary protector must operate. The present K.20 level of 1000 amps is extraordinary. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 [email protected] http://www.randolph-telecom.com
