I'm looking for comments to the following: I just received my copy of the draft proposal of UL1950/CSA 950 to incorporate changes in IEC 950 4th amendment. This was worked up by the Bi-national Working Group for Information and Technology and Telecommunications Equipment. It is dated February 6, 1997.
My concern has to do specifically with section 6.2 "TNV Circuits" in which they have chosen to reduce the peak voltage of a TNV circuit from 120 VDC in IEC 950 and replace it with a maximum of 60 VDC. They did this in UL 1950/CSA 950 3rd edition also. The problem is that this Bi-national standard replaces UL-149 in the year 2000. As such all telecommunications equipment must be tested to this new standard to receive a Listing or recognition Mark from an NRTL. The scope of UL 1950/CSA 950 specifically states that it applies to mains or battery powered ITE regardless of ownership or source of power. This is going to cause a real big problem for equipment that is owned by the telcos since many of the newer technologies rely upon span powering for proper operation. Examples are HDSL, ISDN, T1, and E1. These technologies work by having the central office equipment supply a voltage simplexed with the digital signals over the Outside Plant Cable( telco lines). These voltages allow enough power to be delivered over the telco lines to power repeaters and remote units located at the customer premise. Typically these voltages are less than 140 VDC with respect to ground so that they will comply with Bellcore's Class A3 safety requirements. Most of these devices reside in Industry standard channel banks or telecommunications shelves that are not designed to meet any type of creepage and clearance requirements. Some might meet basic insulation requirements for creepage and clearance at 120 VDC, but do not even come close to meeting reinforced insulation requirements for power supplies that they would need to meet if they have to be classified as power supplies. The telcos want to go farther which means lower power remote units or higher voltages (simple ohms law). They also want span powering since power outages at the customer location do not cause loss of the telecommunications network. As more and more companies install UPS's, they will want to transport voice and data even during power outages. The remote units are already about as low as they can go with respect to power consumption. The span voltages do not appear at the customer side of the demarcation point because the remote unit isolates the network interface from the customer interface and only sends out possibly sealing current(-48 VDC <100mA) and the digital signal. The Baby Bells (RBOC's), GTE, and the independent service providers as well as AT&T, Sprint, MCI etc. now are asking for UL 1459 or UL1950 3rd edition recognition or listings on products they own. Once UL-1459 goes away that only leaves UL1950/CSA 950. As such they could replace all their host systems, shelves, channel banks etc with UL-1950/CSA 950 compliant ones. However that would cost BILLIONS and WOULD NOT BE DONE. Instead they would probably just drop the Listing and /or Recognition requirement. As such the new Telco equipment would not be checked at all for safety and would pose an even greater risk to individuals. I would propose that an exemption be added that states something like the following: Section 6.2 TNV 2 and TNV 3 circuits Exception: Equipment that is owned, operated and maintained by a public utility or telecommunications service provider may have voltages up to 120 VDC on the network interface provided that they meet all other requirements for TNV 2 or TNV 3 circuits and do not pass a voltage above 60 VDC to the Customer side of the telco demarcation point. Any comments please!