*Class lightning protection buildings

1、 The equipment, pipelines, structures, cable metal sheaths, steel roof trusses, steel windows, and other large metal objects inside the building, as well as the metal objects such as exhaust pipes and air ducts protruding from the roof, should be connected to the grounding device for lightning protection induction.

The perimeter of the metal roof should be grounded with a down conductor every 18-24m.

Reinforced concrete roofs cast on site or composed of prefabricated components should have their steel bars tied or welded into a closed loop, and should be grounded with a down conductor every 18-24 meters.

2、 When the net distance between parallel laid pipelines, structures, and cable metal sheaths is less than 100mm, metal wires should be used for bridging, and the spacing between crossing points should not exceed 30m. When the net distance between crossings is less than 100mm, they should also be bridged at their intersections.

When the transition resistance at the connection of long metal objects such as elbows, valves, flanges, etc. is greater than 0.03 Ω, metal wires should be used to bridge the connection. For flanges connected by no less than 5 bolts, cross connections are not required in non corrosive environments.

3、 The grounding device for lightning protection induction should be shared with the grounding device of electrical equipment, and its power frequency grounding resistance should not exceed 10 Ω. The distance between the grounding device for lightning protection induction and the grounding device for independent lightning rods, overhead lightning protection lines, or overhead lightning protection networks should meet the requirements.

The connection between the indoor grounding main line and the lightning protection induction grounding device should not be less than two.

Secondary lightning protection building

When the entire length of the low-voltage line is introduced using buried cables or cables in overhead metal cable trays, the metal sheath of the cable and the metal cable tray should be grounded at the entrance end, and connected to the lightning protection grounding device.

2. Low voltage overhead lines should use a metal armored cable or sheathed cable with a buried length of not less than 2 (m) that is directly buried through a steel pipe, but the buried length of the cable should not be less than 15m. Lightning arresters should be installed at the connection between the cable and the overhead line. Lightning arresters, cable metal sheaths, steel pipes, and insulator iron feet should be connected together for grounding, and their impulse grounding resistance should not exceed 10 Ω.

Buildings with an average thunderstorm day of 30 or less in 3 years can be directly introduced using low-voltage overhead lines, but they should meet the following requirements:

(1) A lightning arrester should be installed at the entrance end and connected to the lightning protection grounding device together with the insulator iron foot. The impulse grounding resistance should not exceed 5 Ω;

(2) The iron feet of the insulators of the three base poles at the entrance should be grounded, and their impulse grounding resistance should not exceed 20 Ω.

The third type of lightning protection building

1、 For cable entry and exit, the metal outer sheath, steel pipe, etc. of the electric winding should be connected to the electrical equipment grounding at the entry and exit ends. When cables are converted into overhead lines, lightning arresters should be installed at the conversion point; Lightning arresters, cable metal sheaths, insulator iron feet, fittings, etc. should be grounded together, and their impulse grounding resistance should not exceed 30 Ω.

2、 For low-voltage overhead incoming and outgoing lines, lightning arresters should be installed at the entry and exit points and connected to the grounding device of electrical equipment together with insulator iron feet and fittings. When multiple circuit overhead incoming and outgoing lines are installed, only one set of lightning arresters or other types of overvoltage protectors can be installed at the busbar or main distribution box, but the insulator iron feet and fittings should still be connected to the grounding device.

3、 The overhead metal pipelines entering and exiting the building should be connected to the grounding device of lightning protection or electrical equipment nearby or independently grounded at the entrance and exit, and their impulse grounding resistance should not exceed 30 Ω.