Classification and Measures for Lightning Protection in Buildings

1. Classification of lightning protection in buildings

According to the importance of the building, the nature of use, the possibility of lightning accidents and the consequences, as well as the requirements of lightning protection, it is divided into three categories:

Type I lightning protection building:

• Any dangerous building where explosives and their products are manufactured, used or stored may cause great damage and casualties due to the explosion and detonation caused by electric sparks.

• Buildings with explosive hazards in Zone 0 or Zone 20.

• Buildings with explosive hazards in Zone 1 or Zone 21 will explode due to electric sparks, causing great damage and casualties. 

Type II lightning protection buildings:

• Buildings belong to key cultural relics under state protection.

• National halls, office buildings, large exhibitions and expo buildings, large railway stations and airports, state guesthouses, national archives, important water supply and pump rooms in large cities and other particularly important buildings.

• National computing center, international communication hub and other buildings of great significance to the national economy.

• National super and class A stadiums.

• Dangerous structures in which explosives and their products are manufactured, used or stored and which are not likely to explode or cause great damage or injury to persons by electric sparks.

• Buildings with explosive hazards in Zone 1 or Zone 21 where the electric spark is not likely to cause an explosion or cause great damage or injury.

• Buildings with explosive hazards in Zone 2 or Zone 22.

• Open steel closed gas tank with explosion hazard.

• Ministry, provincial office buildings and other important or densely populated public buildings and fire hazard places where the number of lightning strikes is expected to be greater than 0.05 times/a.

• General civil buildings, such as residential buildings and office buildings, or general industrial buildings with an estimated number of lightning strikes greater than 0.25 times/a.

Type III lightning protection buildings:

Buildings and provincial archives center belong to key cultural relics under provincial protection.
The number of lightning strikes is expected to be greater than 0.01 times/a and less than or equal to 0.05 times/a in ministry, provincial office buildings and other important or densely populated public buildings and places with fire hazard.

The number of lightning strikes is expected to be greater than 0.05 times/a and less than or equal to 0.25 times/a for residential, office and other general civil buildings or industrial buildings.
Isolated tall buildings such as chimneys and water towers with a height of 15m or higher in areas where the average thunderstorm day is greater than 15d/a. Isolated tall buildings, such as chimneys and water towers, 20mm or higher in height, in areas where the average lightning strike day is 15 days or less per day.

2. Lightning protection measures for buildings

All types of lightning protection buildings should be equipped with external lightning protection devices to prevent direct lightning strikes, and measures should be taken to prevent lightning surge intrusion (external lightning protection system). 

Lightning-sensitive measures (internal lightning protection systems) should be adopted for type I buildings and type II buildings at explosive risk sites. Other types of buildings should also be protected against lightning EMP, especially if the importance of the equipment attached to the building is high.

All types of lightning protection buildings should be equipped with internal lightning protection devices, and should meet the following requirements in the basement or ground floor of the building. The following objects should be connected with the lightning protection device for lightning protection equipotential: building metal body; metal devices; in-building systems; metal lines to and from a building.

The distance between the external surge protection device and the metal body, metal device, and internal system of the building must meet the requirements.

Lightning protection measures for type I lightning protection buildings:

All outdoor low-voltage distribution lines should be directly buried with cables, and the metal skin and steel pipe of the cables should be connected to the equipotential connecting belt or the lightning inductive connecting device at the entrance.

When it is difficult to use the cable in the whole line, the overhead line with reinforced concrete rod and iron cross arm should be used, and a section of metal-armored cable or sheathed cable should be directly buried through the steel pipe. The distance between the overhead line and the building should not be less than 15m.

Outdoor SPD should also be installed at the connection of cable and overhead line. SPD, cable metal skin, steel pipe, insulator feet, and gold tools should be connected together to ground, and the impact ground resistance should not be greater than 30 ohms.

SPD installed should be Grade I (10/350µs) test product, and the impact current Iimp of each protection mode ≥12.5kA. If no outdoor SPD is available, the indoor SPD can be installed in the IP54 protective box.

SPD installed on the communication line should choose Class D1 (10/350µs) high energy test products, and the impact current Iimp≥2kA. 

Lightning protection measures for type II lightning protection buildings:

SPD of Grade I test shall be installed in the main distribution box and distribution cabinet where the low-voltage power supply line is introduced, and SPD of Class D1 high energy test type shall be installed in the terminal box where the electronic system is introduced.

Lightning protection measures for Type 3 lightning protection buildings:

SPD of Grade I test shall be installed in the main distribution box and distribution cabinet where the low-voltage power supply line is introduced, and SPD of Class D1 high energy test type shall be installed in the terminal box where the electronic system is introduced.

When the power line has no shielding layer, the SPD impulse current is calculated as Iimp=0.5I/nm. When the power line has shielding layer or steel pipe, the SPD impulse current is calculated as Iimp=0.5IRs/n (mRs+Rc). 

I ⸺ lightning current (kA), the type I lightning protection buildings take 200 kA, the type II 150 kA, the type III 100 kA;

n ⸺ the total number of external metal pipes and lines introduced underground and overhead;

m ⸺ the total number of conductor cores in the circuit to be determined;
Rs ⸺ resistance of shielding or steel pipe per kilometer (Ω / km);
Rc ⸺ resistance of core wire per kilometer (Ω / km). 

For outdoor line into the building which means LPZ0 zone into LPZ1 zone, the installation of SPD should conform to the above requirements. Near the equipment to be protected, that is, at the interface of LPZ2 zone or higher, SPD of ClassⅡ (8/20µs) test or Class Ⅲ test should be selected for the power system, and SPD of D1 high energy test or C2 fast rise rate test should be selected for the electronic information system.