In the 20th Century, U.S. telcos designed and built a nation-wide Public Switched Telephone Network, complete with outside plant (OSP) infrastructure to deliver Plain Old Telephone Services (POTS) to every home and business in America. It took the whole century, and several generations of OSP people, methods, and materials to do the job. The 20th-Century OSP was built from wood, concrete, plastic, and copper, and telcos went to great lengths to protect it from the elements. Occasionally, the elements won out, and OSP linemen and cable repairmen (now called OSP Technicians) went out and put things right. Fiber and electronics came on the scene in the last years of the 20th Century, mainly to reinforce or replace copper feeder cables. But, as of the turn of the century, The Last Mile was still, mostly, copper.

The 21st Century is full of new challenges and opportunities for U.S. telcos. To meet the challenges and to realize the opportunities, telcos need a new breed of broadband OSP, capable of delivering POTS, Internet and, often, video services as high-speed streams of IP packets. As such, telcos must rebuild the OSP, from the ground up, on a new IP technology foundation, and deploy many more broadband electronics sites to shorten copper loops for broadband services.

As always, broadband OSP must be protected from the elements: rain, wind, dust, and heat. Broadband OSP must be powered, usually by a commercial AC power, backed-up by batteries or by local generators. Broadband sites must have properly designed grounding systems, to protect the broadband equipment and the OSP technicians who work on it. And, the electronics equipment at the sites must be protected from harm by external sources of electrical energy. (See Figure 1.)

Figure 1. Lightning Shield.

Unwanted electrical energy can get into a site by direct contact, by induction from magnetic and electric fields, or by conduction from interconnected electrical conductors.

Remote sites are always equipped with electrical protection devices to intercept harmful electrical currents on the AC power line or other metallic cables entering the site. These devices are designed to shunt harmful currents into the site’s grounding system before they can reach the electronics.

Lightning = Serious Electrical Threat to Broadband OSP Equipment
Lightning occurs during a thunderstorm when a cloud attains an electrical charge of sufficient potential to cause a dielectric breakdown of the air. A lightning strike is the resulting electrical discharge, either between 2 clouds or from a cloud to the earth. Lightning strikes are the most serious electrical threats to broadband OSP equipment, especially at remote sites in rural areas.

There are 2 types of thunderstorms: convection storms and frontal storms:

1. Convection-type storms are caused by localized warming of air near the earth which rises and meets cold air at higher altitudes. Convection storms are localized and are of short duration.

2. Frontal-type thunderstorms occur when a front of warm, moist air collides with a cold front. Frontal storms can extend for several hundred miles and can bombard an entire telco with lightning strikes for several hours.

Thunderstorms occur all over the United States. Their incidence and intensity varies greatly through the year, but they are most frequent in the summer months: June through September, often called the  lightning season. A broadband OSP remote site can be subjected to hundreds of nearby strikes during a single 24-hour period during lightning season. Believe it or not, the electrical potential of a lightning strike is very high, estimated at 5 to 20 million volts. (See Figure 2.)

Figure 2. 24-hour lightning strike record for a remote site in northern New Mexico.

Telecommunications towers and other tall structures are usually designed with low-resistance, high-current paths to ground (i.e., lightning rods) to enable them to withstand a direct lightning strike. Fortunately, the probability of a direct strike at a typical broadband OSP site is miniscule.

But a direct hit is not the only way that a broadband site can be harmed. A direct strike to an AC power line can produce a dielectric breakdown of the surrounding air resulting in an arc between 2 of its phase conductors. The resulting unbalanced condition can cause a surge on the AC line to a remote site. Remote broadband sites are usually equipped with surge suppressors to divert the excess energy into the site’s grounding system.

There’s yet another way broadband sites can be impacted by lightning. Since most lightning strikes are direct strikes to earth, the electrical potential of the earth at the point of the strike rises rapidly and an electrical field radiates outward through the surrounding soil. This electrical field may be intense enough to induce harmful currents on the shield and/or conductors in nearby telecommunications cables. To protect it, the shields of OSP cables entering a remote site are always bonded to the site’s grounding system and their conductors are connected through gas tube or solid state protection devices designed to shunt harmful currents into the grounding system.

As you would expect, rural sites are more threatened by lightning than those in towns and suburbs because there are no nearby tall structures to intercept lightning strikes, and there are no water pipes or other underground infrastructures to dissipate a ground strike’s energy. So, broadband OSP sites in rural areas, even where the incidence of lightning is relatively low, must always be equipped with comprehensive electrical protection and surge suppression equipment.

But, rural sites are vulnerable to another kind of lightning threat.

With direct lightning strikes to the earth, the earth does not provide a very good ground. In fact, dry soil is an excellent electrical insulator. When lightning strikes the earth, its energy is radiated through the soil, sometimes for several miles, until it is dissipated or until it encounters a lower impedance path to ground than the soil itself, such as a remote broadband site’s grounding system! The strike’s energy can momentarily raise the potential of the site’s grounding system to hundreds or thousands of volts. This effect is called Lightning Ground Potential Rise (L-GPR).

If the soil’s resistivity is high, a strike’s potential rise, and the distance it travels through the soil, is greater and farther than if its resistivity is low. Soils that take up and hold moisture (e.g,. loam and clay) have lower resistivity than do sandy and rocky soils. So, a broadband OSP site in a dry, desert area with only an occasional frontal type storm can be just as threatened by L-GPR as a site in a high-lightning area.

If the site’s grounding system is unable to quickly drain off the high L-GPR energy into the earth, the potential will overflow through the site’s master ground bar toward the AC power neutral conductor. This causes a surge on the commercial AC line, albeit in the reverse direction from what is expected.

A surge suppressor device is bi-directional, so it will clamp this surge. This turns the L-GPR current back toward the site ground through the electronic equipment. The electronic equipment is not designed to withstand the excess current trying to flow across it to ground. The results can range from disruptive to devastating.

A modern broadband OSP remote site is densely packed with electronics equipment: a DSLAM, or an MSAN, an Ethernet switch, etc. A single plug-in board can cost thousands of dollars. Damages to broadband plug-ins caused by L-GPR will cost U.S. telcos an estimated $250 million this lightning season. The costs of disrupted operations, interrupted services, and lost customers will take millions more off telcos’ bottom lines.

An Ounce of Protection
Thunderstorms, lightning strikes and L-GPR can't be avoided. However, some telcos have ways to prevent the harmful effects of L-GPR while reducing their costs and safeguarding their broadband OSP investments.

A Lightning Shield system has 2 components: a Detector and a Controller. (See Figure 3.) The Detector senses the electrostatic field of an impending lightning strike. The Controller disconnects site's commercial AC power connection "just in time", before its electronics equipment can be damaged by L-GPR. The L-GPR energy is dissipated harmlessly through the site's grounding system. The site operates on standby power during the lightning threat. Commercial power is restored when the threat has passed. Lightning Shield also protects the electronics equipment from harmful effects of other power line events, such as downed power lines, voltage surges and sags, or high-speed transients.

Figure 3. A Lightning Shield system has 2 components: a Detector and a Controller.

The Controller is mounted near the AC power service entrance, and is wired on the load side of the AC disconnect switch. The Detector can be mounted on any nearby structure. The elapsed time from when the Detector senses the impending strike until the Controller disconnects the AC power line is about 15 ms, "just in time" to avoid damage to the electronic equipment. The Controller continues to poll the Detector during the threat, and, when the threat has passed, it restores the AC power until another threat is detected.

An optional Remote Manager allows Lightning Shield functions and operations to be monitored and controlled from any location. The Remote Manager's capabilities include monitoring the Lightning Shield's current status, configuring its operating parameters, testing its functions, and saving a history of L-GPR events for later analysis. The Remote Manager also simulates a L-GPR event, checks the batteries under load, and checks for proper operation of a back-up generator.

Building to Protect the Future
The National Broadband Plan challenges telcos to provide broadband to everybody, everywhere in the U.S. To achieve this goal, telcos will build thousands of new broadband OSP sites, many in rural areas exposed to lightning. Meanwhile, telcos will upgrade many thousands of existing sites, many in rural areas exposed to lightning.

As always, these the telcos' new broadband OSP must be protected, and the broadband services it carries must be safeguarded from the elements. Because so much of the 21st Century OSP will be electronics, installed in remote sites in rural areas, exposed to lightning, new electrical protection technologies and methods will be required.

Hundreds of remote sites, wired and wireless, from coast to coast, and from border to border, are already shielded from L-GPR, "just in time" for the 2010 lightning season. But, many thousands of existing sites are not shielded, and many new sites won't be protected in time to avoid damage by L-GPR.

The idea is to keep the lightning in the ground, and out of the broadband OSP. Otherwise, better stock up with spare boards!

Just in time.

About the Author
Kermit Ross is founder and principal of Millennium Marketing, a marketing consulting firm specializing in OSP issues and technologies. He has more than 45 years in the telecommunications industry, beginning in OSP Construction at Indiana Bell. He has spent sleepless nights dealing with the effects of lightning. Mr. Ross can be contacted at klross@grandecom.net.

Two Small Telcos Strike Back

Telco A: Seneca Goodman Ozark (SGO)
SGO is a family-owned telephone company located in the southwest corner of Missouri, with telephone, broadband, and IPTV customers in Missouri, Arkansas, and Oklahoma. SGO is an RUS borrower, and, over the last several years, it has modernized its outside plant (OSP) and shortened its copper loops by installing over 85 Next-Generation Digital Loop Carriers (NGDLC) spread across its 6 exchanges. The NGDLCs are used for POTS, special services, and DSL, and SGO has installed broadband IP equipment at all its remote sites to upgrade them for IPTV and higher speed Internet services.

Lightning has always been a problem in SGO’s territory, and the region’s rocky soil just aggravates the problem. By 2007, SGO’s owners and managers, Jay and Brian Mitchell, were fed up with the outages and equipment damages caused by lightning, and were searching for a solution. They found a new company, Alset Corporation, with a new product, Lightning Shield, which offered the most promise.

Alset’s engineers knew that there was no way to prevent Lightning Ground Potential Rise (L-GPR). However, if an impending lightning strike could be detected in time, preemptive action could be taken “just in time” to prevent harm to the electronic equipment at a remote site.

SGO installed a Lightning Shield at a trial site in the spring of 2007, and the results were immediate and dramatic. There were severe thunderstorms with plenty of lightning in the area during the 3-month trial, but no damages at all to the equipment at the site. SGO estimated that the costs of Lightning Shield equipment could be recovered within 1 year or less.

Since then, SGO has installed Lightning Shield at all of its remote sites, with the same dramatic results. Kim Little, SGO’s Assistant Manager, reports that “Lightning Shield has cut our lightning-related damages down to almost nothing. And, our board repairs are down by 80 or 85%. Our remotes used to get torn up a lot by lightning, but it just doesn’t happen anymore.”

Telco B: Sacred Wind Communications
New Mexico’s Sacred Wind Communications is a privately-owned company dedicated to improving telecommunications services in rural areas of northern New Mexico. Sacred Wind started up operations in December 2006 after acquiring Qwest’s local facilities that served portions of Navajo lands and nearby areas in the northwestern Four Corners area.

Sacred Wind is committed to provide advanced telecommunications services, including broadband Internet connections, to its Navajo and non-Navajo residents, to government entities, and to businesses in its territory. It secured a $70 million RUS loan to expand and modernize the facilities it acquired from Qwest in order to provide voice and Internet services to un-served and underserved customers throughout its rural, remote territory.

Sacred Wind is using a combination of advanced OSP technologies, including point-to-point microwave, WiMAX and multiservice access platforms on its existing copper OSP to build 21st Century broadband OSP throughout its 3,200-square-mile service territory.

Where it has existing copper, Sacred Wind is deploying some of the most advanced technologies and products to upgrade it to broadband OSP. Since it is so time-consuming to acquire rights-of-way for new fiber feeders, bonded copper pairs are being used to transport Ethernet links as much as 40kft to new IP access equipment at remote sites.

Where there is no existing OSP infrastructure, Sacred Wind is building new wireless OSP on a common IP technology platform. The wired and the wireless OSP infrastructures are combined by modern soft switches into a common, all-IP, all-broadband access infrastructure to serve the area.

The high-desert region served by Sacred Wind has dry, sandy soil and is subject to frontal thunderstorms, which can have devastating effects on remote electronic sites. And, since the distances are so far, the time and cost to repair a remote site adds up fast. So, Sacred Wind has taken great pains to protect its remote broadband sites from electrical faults and surges caused by lightning and from L-GPR. (See Figure 1.)

SGO and Sacred Wind are two progressive telcos who are building the broadband OSP they’ll need to reach every home and every business with robust and reliable broadband services. They are shining examples that show that broadband can reach everybody, everywhere, and can work reliably in the toughest conditions... even during a thunderstorm!

What’s your take on this subject? Leave a comment and get the conversation going.