One strike and you’re out!
Mother Nature won’t deliver a warning shot, so take measures to guard against lightning-related damage.
High winds from hurricanes and tornadoes can cause significant damage to local government facilities, but another facet can also cause damage – lightning strikes from the storms that are associated with these natural disasters. Fortunately, local governments can take certain precautions to minimize the damage associated with lightning strikes.
Besides the property damage to delicate equipment and potential for serious injury, lightning strikes can bring a major disruption in our ability to serve the public.
Radio and telecommunications systems damage is the most frequent cause of loss, followed by damage to computers. There are also claims involving damage to landfill scales and equipment. While no system will likely survive a direct hit by lightning, it is critical that each facility have a good, low-resistance grounding system to protect against surges caused by nearby strikes.
Electrical equipment damage is usually caused by improper or insufficient grounding or a lack of special protection from a ground potential rise (GPR) – or “outgoing energy.” A lightning strike to a grounding system produces an elevated ground (or GPR). Any equipment bonded to the grounding system and also connected to wire-line communications is likely to be damaged by outgoing current seeking remote ground.
Damage to most electronic equipment can be prevented with methods that are simple, reliable and inexpensive, compared to the cost of repair. The best defense against power surges utilizes multiple layers of protection.
A transient voltage surge suppresser (TVSS) should be installed on the electrical service entrance to protect against surges generated from outside the facility. A second layer of protection should be provided by surge protection devices (SPDs) installed at each distribution panel supplying sensitive electronic equipment. These protect against internally generated surges. Finally, additional SPDs should be installed locally at each piece of equipment.
The outgoing energy from a GPR places most communications and power installations at risk for equipment damage and the people near them at risk for harm. One of the most dangerous locations for personnel and the potential crisis that could ensue from damage to the communications network is a 911 center.
A typical center is a small building beneath a large tower supporting communications antennas – an ideal target for a lightning strike. Communications operators do not have the luxury of staying off the phone during lightning storms, which is a standard safety recommendation.
One North Carolina county incurred an expensive loss when lightning struck its 911 center. Since then, the county has implemented a policy to switch over to generator power whenever an electrical storm is approaching. The practice has eliminated most losses and has the side benefit of helping maintain the generators by running them a few times a year.
Determine the level of risk to your equipment and personnel
To determine the potential for damage or destruction to equipment and injury or death to personnel from a lightning strike, count the number of bullets that describe conditions at your location:
- Lightning damage has previously occurred at the location
- Personnel work and use equipment at the location
- An antenna tower is within 50 feet of the location
- At least 30 days of thunderstorm activity occurs in the location’s area per year
- The location requires AC power but lacks surge-protected power panels
- The location requires wire-line telecommunication services that have not been isolated using optical isolation or isolation transformers
- Equipment at the location is not bonded at a single point on the building grounding system
- Coaxial cables enter the location directly without first going through a bulkhead panel/waveguide hatch
- The location’s associated antenna tower lacks a grounding system consisting of at least 200 feet of buried bare ground conducting wire with multiple paths (minimum of five, each 40 feet in length) away from tower base
- Coaxial cables enter the location at ceiling height (15 to 20 feet above ground level), and all equipment grounding is done at floor level or below
Key elements for proper protection of equipment and personnel from lightning
- Use current division to control the dissipation of lightning strike energy on an antenna tower grounding system through multiple paths.
- Separate an antenna tower from an equipment building by a minimum of 30 feet.
- Use a single-point grounding system for an equipment building.
- Use a bulkhead panel/waveguide hatch for all coaxial cable entering an equipment building.
- Coordinate the location of the bulkhead panel bond, power and telecommunications entry bond, and antenna and equipment building bond at the single point ground connection and building master ground bar.
- Isolate all wire-line communication services from remote ground with optical devices or isolation transformers.
- Use AC power surge protection at main power entry and critical secondary panels.
Information contained in this article should serve only as a guide to determine risk from lightning strikes. For additional information, consult with a qualified company or individual experienced in lightning protection.