From Power Protection—Is Wire Obsolete? Combining Old and New Technologies May Help Telcos Answer Their Power Protection Problems. Part 1 in series, by Russ Gundrum, Telephone Engineer & Management
published on December 15, 1984.
“Bell Communications Research (Bellcore) issued a technical advisory on digital loop carrier (DLC) systems in August, 1984 and sponsored a Technology Requirements Industry Forum (TRIF) on the same subject. It was obvious in this document and during the public forum that DLC is the ‘way to go’ for the operating companies to meet many of the future telecom services, whether DLCs operate over metallic ‘T’-carrier or use fiber optics. However, metallic test pairs are still required for end-to-end testing and metallic pairs up to 12 KF are also utilized from the remote terminal to the customer. (Pronto and GR-303?) It was estimated that only 2.5 million lines would be served over DLC systems by 1990, which is less than 3% of the 111 million combined access lines in the U.S.” (From the January 31, 2002 website of Westell, www.westell.com , broadband market facts:
Today there are about 200 million access lines in the U.S. alone.
About 95% of these lines are copper-based.
The U.S. represents only 15% of the world market for copper-based broadband.
For the next 5 – 10 years, the delivery of broadband services will involve this access network.)
“The Bellcore documentation and forum focused on what the DLC manufacturer’s design criteria should be, as opposed to what the telco facility requirements should be. In many cases, the equipment design requirements for electrical protection and power induction magnitudes were much higher than what you might normally expect on a telephone facility and much greater than what was even allowable from a safety hazard standpoint for trained personnel! While any manufacturer can design his equipment to meet a customer’s specification, that does not necessarily result in the most reliable or cost effective engineering approach when looked at from a total operating system’s point of view. Unnecessary ‘gold-plating’ or over-engineering can result in expensive equipment to purchase and maintain.”
“In this age of bypass, the telco customer definitely has other alternatives to basic telecommunications if better price, quality and variety of services can be provided by another vendor. Hopefully this new technology equipment will result in higher quality and less expensive services to the customer. However, if the customer is paying more and the service doesn’t even work, he/she will definitely be looking for alternatives! This situation is not just confined to the developing countries. They don’t have a lot of personal computer telecom needs. Primarily they just want to be able to talk to one another easily and inexpensively. It may get to that point in the U.S. some day!”
“The power induction story, along with its effect on telephone service, is an old one that has been costly to the entire telecommunications industry. Much of this cost has resulted from the thousands of futile manhours spent annually on attempts to reduce noise and AC induction on telephone lines. Such expenditures failed to buy any permanent relief from the power influence inherent in the types of systems and materials involved in both the telecom and power industry. Many engineers and managers seem convinced that the only solution to these problems is to totally abandon their existing copper plant in some situations and replace it with non-metallic facilities such as lightwave fiber optics or microwave radio. While some may call this ‘new car fever’, it is being done even though it cannot be justified for future growth. Often this approach may be more expensive than alternative techniques, even with new wireline facilities if all aspects are considered.”
“Telcos have traditionally been able to combine old technology with the new, as recently dramatized on a trip to a satellite earth station that was being served over open wire facilities! There were problems with AC induction and protection on the open wire, but they were easily and inexpensively solvable when compared with more costly alternatives.” (Indonesia)
“Telcos spend a lot of money annually trying to cope with AC induction and noise problems. Besides the man-hour expenses, material costs go for such things as gas tube protectors, ringer isolators, improved cable sheaths and ground rods, subscriber carrier systems, CDO’s (RTs), better balanced and less susceptible central office and station equipment, etc. The late Don McLellan of Bell Labs once stated at a 1978 Northwest Inductive Coordination Committee meeting in Seattle, that one-third of the annual maintenance costs in the Bell System, or about $315 million dollars a year, are spent on solving noise problems!”
“Considering that staggering figure of six years ago, it is no wonder that many resources are spent trying to find other ways of transmitting data or voice communications from one place to another!”
“Certainly every technology has its good and bad points, and you would think after 100 years in the wire business, the telcos should understand everything possible concerning wire problems and solutions. Even in 1984 (and 2002), people are struggling and perplexed by this ‘old’ technology, and yet fascinated by the many good things that it still has going for it.”
“Some negative things are definitely known about the new systems when compared to the old, but the harbingers of such equipment are reluctant to mention these points. The new technology is capital intensive and may still be relatively expensive, when compared to upgrading and conditioning existing facilities, especially if the terminal equipment or repeaters that might be required all require backup power. One definite advantage of copper wire is providing power remotely from the central office. Bell Northern Research recently completed a study that found DC powering of computer-controlled equipment economically attractive for systems requiring up to 50,000 watts. Although this study only applied to the main power supply compared to conditioning an AC power line, on a smaller scale, could DC powering remotely over metallic telephone facilities be practically and economically feasible?”
“Another aspect about fiber optic technology that one should be concerned with was pointed out in an October 1983 report prepared for the Electric Power Research Institute (EPRI) by the Illinois Institute of Technology Research Institute on the Mutual Design of Overhead Transmission Lines and Railroad Communications and Signal Systems. The report stated that while fiber optic technology offers the possibility for complete immunity to electromagnetic interference, a number of interference mechanisms may still cause problems:
‘The fiber optic cable may be vulnerable to damage by lightning and faults if the cable has any metal reinforcing wires, wraps or jackets. The metal component of the cable can conduct current under both steady magnetic induction and transient conditions. If the current is intense enough, the heating and puncturing effects of the current and associated voltages-to-ground could destroy the cable.
Repeaters installed in the fiber optic system are just as vulnerable to lightning and fault-current effects as repeaters installed in other systems, such as carrier.’”
“Of course one way to minimize these problems is to keep anything metallic out of the fiber cable. Another way is to not have the metallic jackets or pairs of wire for order wire, fault locate or powering repeaters, associated with ground. If the latter decision is made, you could have a potential safety hazard to the plant construction or maintenance personnel who might come into contact with the metallic conductor and become a path-to-ground for current to flow! Sound familiar?”
“Other considerations about any transmission facility is that one should not be faced with an ‘all your eggs in one basket’ situation. There are events that occur in the real world, such as backhoe operators, who are great at finding your buried cable for you! If this route happened to be used for subscriber DLC systems, a lot of customers could be isolated from total telecom services. Toll routes that go down just isolate a community from the long distance network, leaving local service unaffected. Usually there is adequate alternative toll routing over different types of transmission facilities. This option or luxury may not be available in the local loop situation, however.”
“Training a work force on new equipment when they still haven’t mastered the craft that has been around for over 100 years, will be interesting to watch. New test equipment and splicing techniques can be very expensive and sophisticated.”
“Properly protecting and treating a metallic facility to operate reliably, safely and noise-free is as old as open wire technology itself. Devices such as neutralizing transformers, longitudinal chokes and drainage reactors were developed in the early 1900’s for treating open wire against the effects of power line interference. When the industry moved toward a balanced, two wire transmission facility placed in a heavily shielded (lead) cable, many of these problems were mitigated and the need for additional treatment devices seemingly disappeared. Of course this type of cable facility was connected to rugged electro-mechanical type switching equipment, vacuum-tube type repeaters and 300 and 500 type station sets. This kind of telephone system bought the industry about 40 years of relief from the serious consequences of power induction.” (While also losing a generation of folks that understood it!)