Throughout time people have attempted to protect themselves and their belongings from the effects of lightning. Equipment in today’s computerized world is very susceptible to lightning. However, no magic bullet exists for lightning protection. Protection is achieved only through a careful investigation to identify all sensitive components and all possible paths for lightning currents and voltages, followed by the design, specification, installation and maintenance of a protection system.
Unfortunately, lightning protection methods add cost to the overall site and no solution is fool-proof. The owner/operator of a site must then evaluate the trade off between the risk and the cost of additional protection. The lightning protection devices described can not guarantee no damage will result from a lighting strike, but they can minimize the damage.
Remember that surge protection devices are usually of a sacrificial design. They are designed to take the brunt of the surge while protecting the attached equipment. After a major surge, these devices will probably need to be replaced. Protecting equipment is very challenging, the path a lightning strike will take is impossible to predict. It only takes a portion of the main strike energy to hit sites electronic equipment to damage or destroy it, even if the majority of the strikes energy is directed away from sensitive electrical equipment.
How Lightning Causes Damage
Lightning strike causes damaging transient voltages and current surges that can affect equipment depending on what and where the lightning strikes. This factor determines the effectiveness of the lightning and surge protection and the amount of damage a strike can cause. Lightning can damage equipment in several ways the following describe the most common events:
1. Line Surge - Lightning enters a site through the power utility that supplies the site. This can happen through a local strike or a more distant strike at a power substation. Most substations are equipped with circuit breakers that will trip in the event that a lightning surge hits the substation or the lines that it feeds. In most cases, the circuit breaker causes a temporary power outage. This type of lightning event often causes a major power line surge or spike.
2. Ground Wave – Occurs when a nearby lightning strike sends an electrical surge through the ground. These surges can travel several miles and get picked up by wires installed at or below ground level. They usually cause only temporary interference with any connected equipment. Permanent damage rarely occurs from this type of surge.
3. Direct Strike – When lightning directly strikes a facility, its buildings, or the utility lines immediately adjacent to the site induce very large voltages and currents on all electrical wiring at the facility. A direct strike often damages large parts of a facility and its electrical and computer equipment. Wiring, electrical circuits and computer chips often get vaporized by the very large currents resulting from a direct strike.
Lightning Protection Methods
Lightning protection devices switch the threatening surge to ground around the signal connection point of the protected equipment. Thus, redirecting the threatening surge on a path-of-least resistance (impedance) to ground where it is absorbed. The composition of a lightning protection device includes a switch and a good ground connection to allow dissipation of the surge energy. We cannot emphasize the need for a good ground connection. Computer equipment has been damaged by lightning, not because of the absence of a protection device, but because inadequate attention was paid to grounding the device properly. The configuration of the grounding system depends upon soil conditions, building construction and the presence of other underground conductors.
Installers can create Grounding systems with driven ground rods, plates and possibly a counterpoise, which is a buried cable encircling the site. A counterpoise adds greatly to the protection from earth voltage rises that may injure people standing on the ground.
Grounding improvements can also provide additional paths for lightning currents to flow to earth, thereby minimizing surges. These improvements usually involve interconnecting adjacent conductors, such as structural steel, conduits and ground conductors. Commonly overlooked grounding problems include conduits, metal equipment cabinets and individual components within computer rooms.
Sensitive electronic and computer equipment, and any equipment interconnected by cables over long distances, require the installation of surge suppressers. Many manufacturers provide a wide variety of surge-suppression equipment. Users must take care to select the most cost-effective device to the currents and voltages expected from a severe strike in their region. Installers must place the surge suppressors where they can easily inspect and replace them if damaged by a severe strike.