A Lightning Protection System (LPS) is designed to protect a structure or building and contents from damage caused by the intensely high voltage currents of a lightning strike (often exceeding a 1,000,000,000 Volt Amps). Lightning protection systems act like a Faraday Cage for buildings. Protecting the building and its contents from external electric fields by migrating that energy around the cage instead of through its contents. A lightning protection system offers a lightning strike a low resistance path to ground where the enormous energy is then safely dispersed. A typical lightning protection system includes lightning rods, metal conductors and ground electrodes designed to offer a low resistance path to ground and to take any high voltage currents from a lightning strike away from the structure of the building.
The low resistant path offered by a lightning protection system is very important as high voltage currents from a lightning strike will always take a path of least resistance to ground.
Without lightning protection any grounded object that provides a path to earth will emit fingers of electrical charge called positive streamers upwards into the sky. These positive streamers intercept the downward negative leaders from a thunder storm so creating a channel of plasma air for the giant voltage currents of a lightning strike to travel along. If the grounded object is a building the high voltage currents will then travel along any low resistant paths within that building’s structure causing heat damage. Lightning energy may even jump through the air to reach a better conductive path.
With a lightning protection system, lightning rods or air terminals are strategically sited on a structure to increase the chances of intercepting a lightning strike before it hits the property being protected. The highly conductive lightning rods of a lightning protection system are normally made of copper or aluminium and are designed to emit positive streamers into the air instead of the structure they are protecting. These positive streamers from the rods intercept the negative leaders of a lightning strike drawing the high voltage currents safely into the lightning protection system and away from the building’s structure. A lightning protection system significantly increases a building safekeeping from the damage caused by lightning and not its probability of being struck.
Lightning can be unpredictable and a well designed lightning protection system will take this into consideration. It will be designed so even if lightning does strike the building’s structure first, its large voltage currents will be drawn into the lightning protection system before any serious damage or harm can be done. It will be designed to draw the huge energy away from parts of the building not able to safely carry such large current loads, while at the same time safely utilising other parts that can. Some buildings require a large re-enforced metal framework in their construction. If suitable additional grounding can be provided at its base so it can be utilised as a low resistance conductor able to carry large currents safely to earth.
Roof damage caused by a lightning strike.
Without a lightning protection system structural materials of a building that share the immense loads from of lightning strike can be damaged and this damage is not always immediately apparent. If there is no low resistance path offered by a lightning protection system the high voltage current from a strike will divide to follow every conductive path to ground it can find. The extremely large voltage currents will pass through materials normally considered insulators instantly generating large amounts of heat. Due to rapid heating any porous materials like masonry can shatter violently as the air inside it expands with super sonic speed. Any materials containing moisture from humidity or rain can explode with even more volatility as its water content is flashed to steam. Other materials may suffer different forms of heat damage, become melted or even burst into flames. These events can cause secondary damage to the building’s human inhabitants or contents.
A correctly installed lightning protection system will be designed to prevent “side-flashes” to and from highly conductive parts of the building. High voltage currents travelling through the bonding conductor of a lightning protection system can create large electric potentials when compared to objects near to the bonding conductor. Side jumps to and from objects of different potential can cause damage and fire hazards especially if the building houses flammable or explosive materials. This can be avoided by maintaining the electrical continuity of such objects to a bonding conductor so zeroing any potential difference and allowing any voltage changes to occur in tandem.
Proper grounding is essential for efficiently and safely dispersing the large amounts of energy from a lightning strike. Failure to provide adequate grounding will cause a lightning protection system to be ineffective resulting in property damage and risk to human life. Standard earthing provided to a building by a utility supplier is not satisfactory for grounding a lightning protection system. Different techniques or additional earthing is used to ensure a lightning protection system has strong electrical connection to ground. These include using additional grounding rods, plates, meshes or a Ufer Grounding system (concrete earthing plate with an embedded steel conductor).