Hello Dino, I think you pose an interesting question. I think the best way to approach it is from a historical and safety perspective. First from a historical perspective. The UL 60950 test level of 1000Vrms is actually extremely conservative assuming the equipment is protected by primary surge suppression that is referenced to ground. In some countries, this is not the case. In North America, this is mandated by various regulations and practices at the customer premises. At the C.O. end it is standard operating procedure by all the service providers to protect their investments. The worst case primary protector is a 3 mil carbon block which fires at 600Vac or less. That is why the overvoltage tests are limited to 600Vrms. Even if damaged they almost always fire prior to 1000Vrms. My guess is that UL 1459 and later UL 60950 were concerned about all transients such as lightning let-through, and a 1000Vrms dielectric withstand test was deemed adequate to achieve this goal. However, I doubt you could find a handful of 3 mil carbon blocks still being used to protect T1 services in North America. Most T1's (if not all), will be protected by either gas tubes or solid state protectors which have much lower and reliable firing voltages. Since UL 60950 covers all telecom interfaces generically, it still assumes 3 mil carbon blocks for all the test including overvoltage. This is reasonable since there are probably a few hundred thousand homes that still have 3 mil carbon blocks installed. I have not been able to find a supplier of these in years though, so they eventually will gone. Now for your original question. Since T1's will be protected by gas tubes or solid states in North America, the maximum AC voltage possible between tip/ring and ground will be 300-400Vrms. So there is really no need for higher dielectric strengths from a pure safety perspective. Also, UL 60950 only requires this test if the ground is not reliable. Since most telecom equipment shelves that use bantams have a permanent ground connection, a breakdown does not cause a safety issue, even if it could occur. Originally the bantam style connectors were used for DSX-1 cross connects (intra-building), but due to the cost and size of the larger WECO 310's, these bantam style connections have been migrated to generic use. But again since locations that have these style connections would be unlikely to have carbon blocks as protectors, there really is not a real safety issue. Where this really gets messy from a standards perspective is when you try to use UL 60950-21, in conjunction with UL 60950. Virtually nothing in the network provides the re-enforced insulation that UL 60950-21 requires between RFT circuits (span powered circuits such as T1, HDSL, HDSL2, HDSL4, some ISDN, FT1, DDS and other services) and SELV, TNV1, 2, and 3. Remember that many (actually most) OSP T1's are actually RFT-V's. Even with a NIU installed (which is not legally required), it does not provide re-enforced insulation. So the customer side is still technically RFT-V, following safety standard logic. UL 60950-21 also requires basic insulation to ground. The ILEC service providers (Bellsouth, Verizon, Qwest, and SBC) which participate in T1E1.7 last years advised UL in a letter, that they rejected UL 60950-21 in whole as incompatible with the telecom infrastructure and their practices, and your bantam array and cables are just one example of the incompatibility. But this is just a fraction of the incompatibility. Due to the requirements in UL 60950-21, technically, if the safety organizations (NRTL's) were to properly evaluate any equipment that has interfaces that face toward the OSP network, they would have to be evaluated as RFT's since there is no attempt to provide isolation from RFT's on the service providers side of the demarc. The service providers only adhere to Telcordia GR-1089-CORE section 7 which does not contain any dielectrics or isolations requirements. In other words the service providers requirements (GR-1089-CORE), are incompatible with the consumer requirements (UL 60950-21). More interesting than this is that GR-1089-CORE has no provisions for limiting RFT's (Class A2, or A3) to the end customer at all. It only limits access to Class A3 under normal operating conditions. The UL standards assume that nothing other than TNV1, 2, or 3 or on the customer side of the demarc. However, in the case of a T1 or HDSLx, since there is only one possible termination, the accessibility for GR-1089-CORE is only determined with the T1 or HDSLx terminal adapter operating normally. In this case, the cord is plugged in and there is no access, so GR-1089-CORE requirements are met, even though the voltages to ground may be 200VDC or 400VDC to earth. Note T1 is usually up to +- 130VDC to earth, HDSLx is normally -190VDC to earth, and some newer type remote products are now +-200VDC to earth.
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: [email protected] mailto:[email protected]]On Behalf Of Dino Christy Sent: Wednesday, December 01, 2004 9:59 PM To: [email protected] Subject: Bantam Connectors Isolation Why is it that Bantam connectors/cables are common amongst T1 "outside plant" test gear yet Bantam cable manufacturers commonly spec their cables at 500 or 650VDC isolation. In fact, the three samples I've inspected measured 0.030" between Tip/Ring and Sleeve and when tested, breakdown occured at approximately 1000Vac. Is 0.030" clearance sufficient to withstand 1000Vrms reliably? I always though 0.040" was more appropriate. Section 6.0 of 60950 requires isolation between Tip/Ring and Ground. Can this be achieved reliably using Bantam connectors in "Outside Plant" applications? Is Weco 310 more appropriate for such applications? Dino Christy _____ Do you Yahoo!? Yahoo! <http://us.rd.yahoo.com/mail_us/ aglines/security/*http://promotions.yahoo.com/new_mail/static/protection.html> Mail - You care about security. So do we. ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: [email protected] Scott Douglas [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: [email protected] Scott Douglas [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
