You might want to consider the deployment of the DSL products. GR-1089 and the FCC (although the Telcordia stuff is the most stringent in the world) apply the surges coupled to tips and rings with the chassis frame ground being the return path. Even the ground rise test (2500V, 500 amp) is applied to tips and rings with no primary protector installed. If proper single point low impedance bonding and grounding are assured, the Telcordia model is pretty good. However the reality is that most sites are grounded and bonded inadequately if at all. As such GPR's (ground potential rises) especially at cell sites cause huge currents to flow backward through the chassis ground through back through the longitudinal voltage suppression, through the overcurrent protection and over to the primary protectors that have a different voltage potential on thier ground, and on back to ground. In many cases all the fuses are blown on the tips and rings as well as the TVS devices (such as Teccor Sidctors)are shorted. These surges are thousands or tens of thousands of amps. This phenomena has nothing to do with surges coupled onto telecom wiring, and is becoming a bigger problem each year as DSL equipment is extended into outside plants. It is really a big issue at cell sites with large antennas and the potential for large GPR events. It is even worse with subcontractors with little training or concern for bonding and grounding do more of the installations.
The good news is that proper bonding and grounding will fix the vast majority of these problems. Special primary protectors and special protection gadgets sold by a few companies are not the answer and are simply a waste of money if the equipment itself complies with GR-1089-CORE issue 3 and the bonding and grounding is correct. They in fact generally are less robust than equipment being damaged. The cost is generally the service provider having to roll a truck and the cost of lost service. So trying to protect the equipment better due to poor installation of grounds simply may cause more truck rolls and more loss of service, although the equipment may not be damaged. However the reality is that the equipment is under warranty on carrier class equipment for 5-10 years and replaced free. So from a business standpoint (all costs considered), it is better to let the equipment get damaged than to put gadgets or special primary protectors on lines. The REAL solution is proper bonding and grounding. The other possibility although it seems to be much more rare, are components rated for GR-1089 being damaged due to being installed in circuits where the primary protector is defective, has gone totally bad, is missing, or where a near direct strike occurs and the secondary protection fires before the primary protection. If gas tubes or 3 mil carbon blocks are the primary protectors, nobody knows they go bad until equipment is damaged as thier failure mode is open circuit. Another thing to remember is that GR-1089 does not model lightning. What it models is the theoretical let-through of a coordinated 3 mil carbon block primary protector which are not used any more that I know of. Gas tubes and solid state protectors are generally much more forgiving with lower and faster firing voltages, so GR-1089-CORE lightning tests are probably major overkill these days. But it is worst case based on Bellcores original study in TR-EOP-00001 and 3 mil carbon blocks. Just remember GR-1089 does not properly test for GPR's. Jim Jim Wiese NEBS Project Manager/Senior Compliance Engineer ADTRAN, INC. 901 Explorer Blvd. P.O. Box 140000 Huntsville, AL 35814-4000 256-963-8431 256-963-8250 fax [email protected] From: Anil Allamaneni [mailto:[email protected]] Sent: Tuesday, August 05, 2003 11:37 AM To: [email protected]; [email protected]; [email protected] Cc: [email protected] Subject: Lightning Surge Characterization/Standards Greetings folks, We have products that meet all the Surge requirements of NEBS GR-1089, FCC-68 and EMC 4-5. But, the same products are continuously failing in the field due to real-world lightning strikes. I have spoken to four other manufacturers who make similiar interfaces (DSL) and they all have the same problem : they meet the standards, but fail in the real world. I have two questions for the esteemed people here : 1) Were these standards written based on somebody doing some field evaluations? Has IEEE/Bellcore done any research into what the waveforms really are for actual *real-world* lightning strikes? How do they do that? 2) Is somebody working on re-charaterization of lightning strikes throughout US (eg, the surges seem to be more lethal in TN as opposed to CA)? Would you have the contact details of Working Groups? Thanks [email protected] __________________________________ Do you Yahoo!? Yahoo! SiteBuilder - Free, easy-to-use web site design software http://sitebuilder.yahoo.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 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
