A look at this modern-day construction challenge, which requires the coordination of architects, civil engineers, electrical engineers as well as lighting protecting experts.
The purpose of this article is to explain the modern way of protecting the contents of a building against lighting and its associated Electro Magnetic Pulse (EMP). Improvement in the current construction techniques is necessary to increase the protection of a building against lighting and its effects. Systems followed in most of the buildings now are unfortunately not meeting the basic or statutory requirements. Implementation of new IS standard for Lighting Protection IS/IEC 62305 opens a new topic of discussion, which has been in practice internationally for several decades. Effective protective measures should start from the foundation, and it is not the electrical engineer, but the designers and civil engineers involved in the preplanning of the building who should start and implement the techniques from foundation onwards. The new techniques will not influence the aesthetics of the building while routing the down conductor on the wall as well as improve the efficiency of the building against LEMP. The modern protection techniques avoid routing of down conductors through shafts and will reduce the chance of fire during lightning. This is also the cheapest and efficient way of protection in a new building.
Lightning protection is often a challenge for the building designer when it comes to aesthetics of the building. Routing of down conductors through outer wall generally spoils the aesthetics of the building, due to which the down conductors are often routed through shafts, un-accessible areas, non-visible places, etc. These down conductors increase the chance of fire and explosion in case of lightning. As a matter of statutory requirement lightning protection is implemented in most of the buildings, but unfortunately is an inefficient way. There are no devices or methods capable of modifying the natural weather phenomena to the extent that they can prevent lightning discharges. Lightning flashes to, or nearby, structures (or lines connected to the structures) are hazardous to people, to the structures themselves, their content and installations.
Lightning protection not only protects the structure against a direct lightning strike, but also protects modern electronic installations in the building. A recent study in Germany conducted by an insurance company reports that about 65% of failure in electronic systems are due to surges created by direct and indirect effects of lightning.
An EMP is a short burst of electromagnetic energy. Such a pulse may occur in the form of a radiated field or a conducted electric current depending on the source and may be natural or man-made. EMP has become a known subject nowadays due to science fiction movies and is also one of the widely researched subjects where modern military weapons with EMP emissions are developed that can destroy electronic systems in specific places. Lightning is the largest natural EMP whose effects can destroy electronic equipment in a large area. This is due to the induced transient voltage in long wires created due to the magnetic field of lightning. Various studies proved that the effects of Lightning EMP (LEMP) can be felt as far up to 2 Km's radius from the point of lightning strike. Modern electronic equipments are sensitive to electrical and electromagnetic disturbances in the installed environment. Reducing the effects of LEMP by the way of Shielding and bonding will protect this equipment. Here comes the role of structural/ civil engineer. By adopting simple improvements in the steel reinforcement in a building, the protection measures against LEMP can be achieved.
Techniques adopted nowadays in most of the high rise buildings do not meet the requirement of LEMP protection measures, but invite additional problems. One example is a single down conductor for lightning protection in a building. Lightning current passing through one metallic conductor creates a large amount of EMP radiation, whereas the same current if routed through 10 conductors reduced the effect by 10 times. The new standard of Lightning protection IS/IEC 62305 recommends the use of naturally available steel in a building such as steel reinforcement as down conductors and earthing. This concrete encased conductor connected to the building steel, making the building steel effectively grounded, is not only an effective system, but cost efficient too. The availability of large amount of down conductors achieved by interconnecting the natural steel will reduce the EMP effect to a large extent. Interconnected concrete encase steel will work as “Faraday Cage” and limit the LEMP effects of a nearby and distant lightning strike too. Equipotential bonding of different steel installations and steel reinforcement in a building reduce the failure of electronic equipment.
This method of Equipotentialisation (Protective Bonding) is well accepted and proven for many decades in developed countries. PED buildings with metallic roof, metal wall cladding and main structure - if all are interconnected together satisfying basic bonding requirements will ensure the protection of industrial electronic against EMP. But in general, the basic bonding measures are not followed now or the purpose is not understood well.
Earthing of electrical system in a building is assumed and followed as a connection to soil with a metallic media such as rod/pipe or plate. In America, the national electric code does not favour the use of an earth rod/pipe/plate. It recommends to use of metal underground water pipe, metal frame of building, concrete encased steel in foundation or a ground ring as earth electrode. Buildings without these only need a rod, pipe of plate for a connection to earth. Where as in India even though the Indian standards, which are in practice for several decades. Recommend the use of steel in foundation as earthing; it is followed only in very few industrial installations.
Purpose of earthing for safety and for safe operation of a protective device is often overlooked and hence the belief of connection to earth rod in soil with a very low resistance value is given more importance in India.
Building with electronic installations need either foundation earth or ring earth for the reliable operation of the installation as strongly recommended in IS/IEC 62305-3. Such an earthing system provides Equipotentialisation and hence the effects of transient currents are reduced. Statutory requirement of "earth pit" with a disconnector is not mandatory, if foundation earth is used. The belief of concrete encased foundation is often viewed with suspicion, due to the myth that "Concrete is an insulator".
Concrete used for the foundations of buildings has certain conductivity and generally a large contact area with the soil. Therefore bare metal electrodes completely embedded in concrete can be used for earthing purposes, unless the concrete is insulated from the soil by using insulating material against ingress of water. Due to chemical and physical effects, bare or hot-dip galvanized steel and other metals embedded in concrete with a cover depth of more than 50mm are highly protected against corrosion, normally for the whole life-time of the building.
Creation of a concrete-embedded foundation earth electrode during the erection of the building is an economical solution to obtain a good earth electrode with long life because:
It addition, the concrete-embedded foundation earth electrode provides a good basis for the main protection bonding. If insulation measures against water (e.g. using plastic sheets of more than 0.5mm thickness) are used, earthing using the foundation concrete is not viable. In such cases, the positive effect of metal reinforcement for protective bonding may be used, and for earthing purposed another earthing arrangement should be used, e.g. an additional concrete-embedded foundation earth electrode below the insulated foundation, or an earthing arrangement around the building or a soil-embedded foundation earth electrode.
Special care, material and expertise are required to avoid corrosion in places where the steel inside concrete is exposed outside. The newly published IS/IEC 62305 provides detailed information about the special measures. Implementing these protective bonding techniques along with surge protective devices for power, voice, data, communication lines etc in new buildings not only saves cost, but will effectively protect electronic system against EMP including the ill effects of lightning.
Implementations of modern lightning protection methods need coordination between architect, civil and electrical engineers as well as lightning protection expert. Implementing the protection measures from foundation onwards is cost effective, efficient and do not influence the aesthetics of the building. The system can be efficiently implemented in places where space is the major constraint for earthing in high rise buildings. This also avoids frequent inspection of installation and problems due to corrosion and theft. The installation is permanent and its life is equal to the life of the building.