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!
