Communications surge protection: From zip to Zap
Power problems or lightning strikes at public safety answering points (PSAPs) are costly not only because of equipment damage but also because of interruption of critical police, fire and ambulance services. Migration to computers by public safety agencies over the past 10 years has been a costly investment. Destruction has occurred because the plant environment is not suited, in many cases, for communications center needs.
There are over 7,000 public safety agencies across America. Most are police and fire departments, many of which are manned by volunteers. What do these centers typically require? They have a radio antenna, a few hundred thousand dollars in computer-aided dispatch (CAD) consoles, a telephone switch and a lot of software. Most of this infrastructure gets tied to a copper rod driven in the ground and clamped with a pair of pliers. Usually, four types of telephone circuits feeding the building: 9-1-1, police administration, old seven-digit numbers and data lines for outdial to search databases or to retrieve automatic location information (ALI) for the 9-1-1 caller. Most of this is in a single, 100-pair cable. Most of it is protected with cheap carbon protectors that cost the phone company a buck each. We have proven that is not good enough.
All the old vacuum tube radios are gone; all the black IA2 copper-driven key sets are gone. Mostly, there is an absence of good design and an absence of grounding standards specific to 9-1-1 facilities.
Who can use new standards? Public safety answering points (PSAPs) receiving 9-1-1 calls are of primary interest. The Institute of Electrical and Electronics Engineers (IEEE) has sought standards changes for many years since PSAPs began using low-voltage logic circuits instead of 1250V plate currents to do business.
The National Emergency Number Association (NENA; I joined in 1984, when there were 40 members. There are now more than 5,000 members.) has also written standards for 9-1-1. The results of this work include FCC-adopted regulations, operability standards, training, telecommunications device for the deaf (TDD) and data formats for location information-but “zip” for the protection of equipment.
It would be expected that the National Electrical Association, Underwriters Laboratories, the National Fire Protection Association (NFPA) and the Association of Public-Safety Communications Officials-International (APCO) would also have a concerned interest.
The problem close-up My own interest started out local, and specific, 13 years ago. The Greater Harris County (TX) 9-1-1 Emergency Network (GHC 9-1-1 ENET) is a communications district created in 1983. The network covers 2,400 square miles, including Harris County, the city of Houston, 36 smaller municipalities and Fort Bend County, which together contain over 152 public safety response entities. The network receives telephony from several dial tone providers that service over four million people in Harris and Fort Bend counties. This 9-1-1 network has been branded the “Ultimate Real-world 9-1-1 Lightning Lab.” Thirty-three massive El Nino-related storms have encroached on this network, which is one of the highest frequency lightning strike areas in the United States according to Global Atmospherics of Tucson, AZ.
Lightning strikes in this region of east Texas are above normal both in quantity and volume, because of both geography and geology. Moisture-laden air masses from the Gulf of Mexico collide with warm air masses in the Houston area, 50 miles inland, producing numerous strikes, both cloud-to-ground and ground-to-cloud. Additionally, the region sits atop numerous piezoelectric faults and is strewn with natural salt domes and man-made oil pits for which lightning strikes seem to have an affinity. Meteorological conditions in recent years have seen an increase in the severity of the lightning problem. For example, in the area of Missouri City, TX, (a Houston suburb) last November, we recorded 2,215 strikes in one 8-hour period, including 40 or 50 strikes on a single police radio tower. Ground strikes as strong as 2159kA have been documented.
Since 1987, 21 of 39 sites in our network have experienced from one to four strikes, including a massive strike at the Houston police communications center. As a result of my responsibilities for design and repair of the emergency network systems, I set out years ago to find a better way to protect millions of dollars of public safety equipment-all critical, all requiring maximum uptime-from this assault.
Experimenting with protection schemes over time, I developed the following axiom: “When the mass of the ground exceeds the mass of the gear, you will improve your survival, and equipment survival, significantly.”
Over time, the program steps became: * to install silicone avalanche diode line protection on all
communications and power circuits entering the building, not just the critical ones. * to move the antenna away from the building-at least 50 feet, if possible. * to bond the main bus and the sub panel to the critical equipment. * to use copper coating paste on all lugs. * to use clamping at 400 torque pounds. * to install center conductor shunt to ground on all coaxial feeds from the tower antenna. * to ring the tower with halo grounding. * to remove all improperly grounded devices entering the call-taking area. * to secure all elevated computer flooring to the common ohm level. * to scope all power 5V to ground, and 3V peak-to-peak on the neutral ground. * to have all installation performed by experienced communications grounding specialists.
These concepts, with a few additional refinements, have been developed over the last 10 years, and comply with NFPA 250.1 and 750.1. They are the keys to banking your equipment protection investment.
Demonstrated success Our uptime is now at 100%. We have extended the life of all tariffed or owned equipment and achieved better performance from the computers-the noise is gone. (In fact, after we had cleaned up the grounding at one police center, mobile officers thought there was a new radio at the base.) Overall, our callouts have been reduced by 92%. In addition to protecting the equipment, the best result is that it protects our people.
In our experience, a minor change in the method of bonding the main bus panel and the critical 9-1-1 equipment will save millions of dollars of damage caused by lightning strikes. It will also reduce noise on building ground to virtually zero volts. Grounding is not enough. Well-designed, quick response devices for power protection, line protection and coax protection all play a major role in proper design.
In applying these techniques to our facilities, we have found that a commitment to apply an investment equal to 10% of the capital budget for the equipment that is to be protected is crucial to accomplishing adequate protection. The alternative is someday having to find the budget to replace the full investment. As an example, we received a severe strike at the Pasadena, TX, facility that destroyed about $1 million in radio equipment, owned by the city of Pasadena, that was not yet three months old. Implementing the above procedures cost $60,000-which had an immediate payback one week after we finished, when a 40kA strike hit the same facility, and nothing happened.
Our team has redesigned grounding methodology with maximum payback, speedy installation and minimum investment. The scheme has been in place in over 80 police, fire and other call-taking centers. The plan has successfully reduced the impact of lightning and power over a ten-year period to near-perfect protection. Noise is eliminated from the power provisioning element of each LAN, virtually eliminating computer rebooting.
Historical data documenting the near elimination of damage in the Greater Harris County 9-1-1 area might be enough to satisfy us locally, but to recommend these procedures as a broader model, more proof needs to be in the pudding; that is, proof by simulation.
If we build it, then we’ll know Ideally, the proof would require building a look-alike police department that could be subjected to man-made simulators, rather than “waiting for lightning to strike” an actual facility. The replica building would be constructed as if for actual use and equipped with the hardware used in police communications, including an antenna, working CRT screens, printers and other devices collected as salvaged but working equipment. This would create actual conditions for rigorous testing to prove the application of these basic bonding techniques. The mock-up site would be protected to the maximum level we could determine, using our methods, then “destroyed,” incrementally, with takedowns of protection and grounding, until it equaled a typical site. The testing and results could be recorded on video, as well, for dissemination into the public safety communications community. This visual would be easily understood and would provide public safety and commercial executives an opportunity to understand the need to invest 10% of the original capital budget for protection and grounding.
It was decided that the concepts-which can be used to define minimum grounding and power protection for thousands of public safety facilities through NENA, APCO and national electrical standards-would have more merit and generate more acceptance of the results if conducted at the engineering level and monitored. To accomplish this project, GHC 9-1-1 ENET is cooperating in a joint venture with Fowler Engineering, Houston, which will provide historical data and manpower for testing and recording, and Northern Technologies (NTI), Liberty Lake, WA, which will provide lightning simulation facilities and engineers. GHC 9-1-1 ENET will ship used, but working, devices and technology salvaged from its centers to NTI for the project. The simulation, conceived in 1996, has come to be known as “Project Zap.”
Project Zap involves the simulation of a police department’s electrical infrastructure at NTI’s Liberty Lake facility and subjecting it to NTI’s “Big Blue” lightning generator, which can produce an 8320 waveform. Now in its final planning stages, the project, expected to begin this summer, will be covered in a future article.
Summary We have compiled 12 years of historical data, showing near elimination of lightning damage at our facilities in the Greater Harris County 9-1-1 area. We anticipate that monitored testing at NTI will further prove the need to have new protection standards for communications centers, both public and private.
Grounding equipment solves equipment damage problems at cellular site A lightning strike at a telecommunications tower can fry expensive radio equipment. One New Jersey-based engineering firm dealt with this problem for a New York state cellular provider.
The cellular company’s vulnerable equipment included receivers, transmitters and couplers-equipment valued in the millions of dollars. The site included three transmitting antennas and six receiving antennas located on a mountain top in southeastern New York state, near Harriman. Whenever a thunderstorm would occur, it was liable to large lightning strikes.
“It’s well known that large towers are very good lightning rods. For example, the towers near Harriman were not only getting hit, but they were sustaining a lot of damage to the equipment inside [the shelters], which is a good indication that there was a grounding problem,” said Kevin Leary, P.E., managing director of The Avoca Group, Watchung, NJ. “Basically, it was blowing out circuit boards in computers and radio equipment,” said Leary, who is an electrical engineer.
Avoca is an engineering and planning consulting firm primarily involved in consultation, design and planning for the construction of paging, cellular, PCS, satellite, E-911 and cable TV systems. In the site preconstruction phase, Leary said, one of the first things Avoca does is test the site soil resistivity to determine how suitable the soil is for grounding requirements. That information is then given to the construction contractor.
To solve the problems at the Harriman site, Leary first tested the existing grounding system in place: conventional ground rods installed in drilled holes in solid granite. He discovered that the original construction contractor had backfilled the drilled rod holes with material that had washed away over time, leaving the grounding rods rattling loosely in open holes. The ground resistance was high, 50V to 60V. After assaying the rocky soil, Avoca sent the data to a company that specializes in grounding systems.
“We told them that we had a real problem here since the soil was so rocky. It was not at all the normal type of site that we work with in this part of the country. We usually have at least some kind of soil and ground cover to work with, but this was basically solid granite,” Leary said. “Plus, we needed to be able to re-install rods with the least amount of on-site work, because it was such a steep, mountainous area. We had to use a truck-mounted drilling rig that would make it up the twisting, switchback road. We couldn’t do any blasting, and it was heavily wooded. So it was a real challenging job.”
“Lyncole, the company we use for grounding systems, was able to evaluate a very difficult site situation and find an economical, efficient solution,” Leary said.
Lyncole Industries, Torrance, CA, has been developing and supplying precision grounding systems since 1968. Its leading product is the XIT grounding system. The company also performs on-site system installation, ground testing and educational seminars, and distributes its own testing and monitoring equipment.
Because every site has different soil conditions, no two grounding grids are identical. Analyzing and interpreting soil conditions are important steps in designing a precision grounding system. Extremes in soil moisture, ambient temperature and soil content need different grounding specifications.
An effective grounding system should be more than just a copper pipe attached to a strand of wire. For example, Lyncole starts with a high-quality, 2″-diameter, copper tube with an exothermically welded pigtail. Breather holes are drilled at the top to bring in moisture, and weep holes are placed along the length of the tube in order to form electrolytic roots. The tube is filled with Calsolyte, an electrolytic compound that attracts moisture from the air. The rod is then inserted into the earth and surrounded by a backfill of bentonite clay material Lyncole supplies under the trade name Lynconite.
Over time, the clay increases in density, adhering to the rod surface and creating an excellent conductive medium with the surrounding soil. The clay is non-corrosive, with a pH of 8.0, and also protects the rod from acids in the soil. The clay has a resistivity of 2.5V/m, which in conjunction with the electrolytic solution inside the pipe increases the overall effectiveness of the system. The system is designed to improve performance over time and provide a seasonal stability.
At the Harriman cellular site, four new holes were drilled for locating the new rods in a 100ftx100ft base area. V-shaped notches were cut in the granite for placement of the ground wires, which were then covered with a concrete material.
Leary said one of the benefits of using the bentonite clay backfill material that Lyncole supplied is that it retains moisture and expands, so it is not as likely to wash away over time.
“This tremendously improved the grounding problem at this site,” Leary said. “We got the ground resistance way down, below 10V, which is very good, thereby solving the lightning damage problem.”
“The savings that come into play when using an efficient grounding system are that you’re eliminating downtime when electronic equipment has to be repaired. Also, the high cost of replacement parts for damaged equipment can be avoided,” Leary said. “Many companies think that they don’t have the time or manpower to worry about installing a good ground, but this sort of thinking can get them into trouble in the long run.”
Pickett is director of operations for the Greater Harris County 9-1-1 Emergency Network, Houston. Contributions to this article were made by Northern Technologies, Liberty Lake, WA, and Fowler Engineering, Houston.
