LPS System as per NBC 2016 & IEC-62305

When lightning strikes at a point, it brings down a huge amount of charge, which flows in all directions until all the charges are neutralized by opposite charges in the earth. There could be charges flowing from surrounding areas towards the point of strike too, as a bolt of lightning has short pulses of current going up as well as coming down. As the charges flow along the ground, constituting and electric current, it produces voltage difference between points. The voltage difference depends on the amount of current flowing (I) and the resistance between the points (R). This voltage difference is given by the equation V = IR. Obviously, the value of R is determined by several factors such as the conductivity of the soil (which in turn depends on the moisture in the soil) and the distance between the points. Therefore, if the points are separated by a large distance, the resistance will be large and the voltage also will be large. Such voltage between two points on the ground separated by a distance is called step voltage. As the current in a lightning bolt is on the order of tens of kilo amperes, the voltages also can be very large. Therefore, if you happen to be near the point where lightning strikes and you happen to be standing with your feet apart or lying down on the ground, you could experience a large voltage between your feet touching the ground or between your feet and your head. In the former case, you could get a nasty shock on your legs as the current enters your body through one leg and leaves through the other. This could cause you to lose your balance and fall or be thrown over a short distance. In either case, you could get hurt, sometimes seriously too.
If you happen to be lying down, the voltage difference will be much larger and the lightning current could flow through your body, from head to toe or toe to head. In either case, it passes through your torso. A tiny part of it could go through your heart, in which case, it could result in the fibrillation of your heart, which could kill you if you don’t get immediate medical care.
Lightning can happen in different circumstances. The most common among them is the thunderstorm or technically, the Cumulonimbus cloud. Lightning can also happen during volcanic eruptions and dust storms (possibly in other situations too). But we will discuss only how lightning happens in Cumulonimbus clouds.
Cumulonimbus is a huge type of cloud that grows from about 1–2 km height above the earth’s surface to the top of the troposphere (the lowest layer of the atmosphere), also known as the tropopause. The tropopause is at a height of about 17 km in the tropics, but comes down to about 11 km near the poles. Therefore, cumulonimbus clouds are about 15 km tall in the tropics, but only about 10 km tall in the temperate regions. There are mainly three types of cumulonimbus, namely, the single-cell type, the multi-cell type and the super cell type. The last one is much bigger and can be a couple of hundred kilometers in diameter, but they grow only when there is vertical wind shear, that is, when the direction of the wind changes with height. They are much more destructive than the single cell type that we see mostly in this part of the country (South-West coast of India). Single cell thunderstorms are usually about 20 km in diameter. The peculiar feature of thunderstorms is that, as they grow so tall, they cross the level in the atmosphere where the temperature falls to zero. Therefore, these clouds have water in all three states in them, namely, water vapor, liquid droplets and small ice flakes.
In a process that is not yet clearly understood, the presence of the three phases of water and the powerful circulation inside the cloud causes electrical charges to separate with the positive charges moving mostly up and the negative charges moving mostly down, though we find charge accumulations in other parts of the cloud too.
While air is normally an insulator of electricity, when the charge accumulation continues for some time and the electric potential differences increase beyond a certain limit, the insulation of air brakes down and electrical energy starts flowing through it. As you know, a flow of electricity through any material causes it to heat up. So air also heats up. As the current that flows through air in a lightning discharge is huge, around 30,000 amperes, this causes the airt in the channel to become extremely hot, again around 30,000 C. This is about five times the temperature of the surface of the Sun. So, the air expands suddenly, causing a shock wave, which we call thunder. Hope this clears your doubt.
Lightning is formed by the the most air inside a cloud being buffeted by the winds. The droplets of water and ice rub together and a static electric charge is produced. It's a bit like when you pull a jumper made of certain synthetic materials over your head and in the dark you can see tiny sparks or arks of energy.

Benjamin Franklin invented the Lightning Rod in 1753. This lightning conductor is made up of a 2 to 8 m high tapered metal rod that dominates the structure to be protected and which is connected to minimum two down conductors and two earthing system.
As the protection radius of this type of Air-Termination Rod is limited to around 30 meters environ (Lightning Protection Level = IV, height = 60 meters), it is normally only used to protect small structures or zones such as pylons, chimneys, tanks, water towers, aerial masts, etc...

Protection of an external explosive storage area by a catenary wire lightning conductor
This lightning protection system, using a similar principle to that of the mesh cage, consists of a mesh of conductors, but at a distance from the structure to be protected. The aim is to avoid the lightning current coming directly into contact with the structure.
Catenary wire conductors placed above the structure to be protected are connected to down conductors and dedicated earthing systems. The size of the mesh and the distance between down conductors are subjected to the same rules as for the meshed conductors lightning protection system.
This protection requires that additional mechanical studies (resistance of materials for masts, qualifying ground pressure, resistance to wind and weather condition, etc.) be carried out and insulation distances defined.
The catenary wire lightning conductor is particularly used to protect open areas when there is no architectural support or hazardous storage.

According to this method, conductors forming a mesh should be placed on the structure. The separation depends on the protection level:

Protection level	Mesh	Distance between down conductors
1.	5 x 5 m	10 m
2.	10 x 10 m	10 m
3.	15 x 15 m	15 m
4.	20 x 20 m	20 m

This method is based on an electrogeometric model that assumes that the last step of the downward leader can propagate in any direction. The model represents this with a sphere (of different radius depending on the required protection level) whose centre is the end of the lightning downward leader. This sphere is rolled along the external surface of the structure to be protected, so that the points in contact with the sphere are susceptible to get a lightning strike.
According to the Standard IEC 62305-3, the rolling sphere radius depends on the protection level:

• •   Protection level I: D = 20 m
• •   Protection level II D = 30 m
• •   Protection level III D = 45 m
• •   Protection level IV D = 60 m

A low impedance bonding network is needed to avoid dangerous potential differences between all equipment inside the building. Moreover, such a bonding network also reduces the magnetic field, thereby reduces the radiated surges inside the building and provides more protection for electrical/electronic equipment. This can be realized by a meshed bonding network integrating conductive parts of the structure, or parts of the internal systems, and by bonding metal parts or conductive services at the boundary of each LPZ directly or by using suitable SPDs. The bonding network can be arranged as a three-dimensional meshed structure with a typical mesh width of 5 m (see Fig. 24 and Fig. 25). This requires multiple interconnections of metal components in and on the structure (such as concrete reinforcement, elevator rails, cranes, metal roofs, metal facades, metal frames of windows and doors, metal floor frames, service pipes and cable trays). Bonding bars (for example, ring bonding bars, several bonding bars at different levels of the structure) and magnetic shields of the LPZ shall be integrated in the same way. Conductive parts (for example, cabinets, enclosures, racks) and the protective earth conductor (PE) of the internal systems shall be connected to the bonding network.
Materials and Dimensions Copper and aluminium are recommended for exposed areas on installations required to have a long life. Galvanized steel may be preferred for temporary installations such as exhibition centres. Although it is a common practice to use material in the form of strip for horizontal air-terminations, down-conductors and bonds, it is more convenient to use round material,particularly as it facilitates the making of bends in any plane. If different materials are used in an installation, care should be taken to avoid galvanic corrosion by the use of bi-metallic connectors.