Question: Is it acceptable to install only one grounding wire for a storage tank?
Answer: No. Two grounding wires should be installed to provide both lightning protection and ensure effective static electricity discharge. The purpose of setting up two grounding points for storage tanks is primarily to guarantee the safety and reliability of lightning protection and static electricity prevention.
From the perspective of lightning protection, storage tanks, as large metal containers, are prone to becoming targets of lightning strikes during thunderstorms. If only one grounding point is installed, once that point fails due to corrosion, loosening, or other reasons, the tank may lose grounding protection. When struck by lightning, electric charges cannot be discharged in a timely manner, which could easily lead to dangerous incidents such as fires or explosions. Two grounding points create redundant protection: even if one point malfunctions, the other can still function, reducing the risk of lightning strikes.
For static electricity prevention, static electricity is generated when materials rub against the tank walls or pipes during storage and transportation. Accumulated static electricity can generate sparks when it reaches a certain level, triggering safety accidents. Two grounding points can discharge static electricity more quickly and evenly, preventing excessive local accumulation of static electricity and improving the effectiveness of static prevention.
In addition, large storage tanks have a large volume and occupy a large area. Two grounding points can reduce grounding resistance, ensure the effectiveness of the grounding system, meet the strict requirements of relevant safety standards for grounding protection in flammable and explosive areas, and provide dual protection for the safe operation of storage tanks.
Therefore, enterprises should strictly comply with relevant standards, implement the requirement of dual grounding in the design, construction, and operation and maintenance phases, and regularly inspect the grounding resistance and cable connection status.
Main Basis:
-
SH/T 3552-2021 Code for Construction and Acceptance of Petrochemical Electrical Engineering
4.4.6 For equipment or vessels with a diameter of 2.5m or more, or a volume of 50m³ or more, there shall be no fewer than 2 grounding points. The grounding points shall be evenly arranged along the outer edge of the equipment or vessel, with a spacing of no more than 30m. They shall be symmetrically connected to the grounding body around the bottom of the equipment or vessel, and the grounding body shall form a closed loop.
-
SH/T 3097-2017 Code for Design of Static Electricity Grounding in Petrochemical Industry
5.1.2 For equipment with a diameter of 2.5m or more, or a volume of 50m³ or more, there shall be no fewer than 2 grounding points. The grounding points shall be evenly arranged along the outer edge of the equipment, with a spacing of no more than 30m.
-
GB 50057-2010 Code for Design of Protection of Structures Against Lightning
4.3.10 For open-air steel enclosed gas tanks with explosion hazards, if their height is ≤60m and the roof thickness is ≥4mm, or if their height is >60m and both the roof thickness and side wall thickness are ≥4mm, no air-termination system is required, but grounding shall be provided. There shall be no fewer than 2 grounding points, the distance between the two grounding points should not exceed 30m, and the impulse grounding resistance of each grounding point shall not exceed 30Ω.
-
GB 50650-2011 Code for Design of Lightning Protection of Petrochemical Plants
5.5.1 Metal tanks shall be grounded for direct lightning strike protection, with no fewer than 2 grounding points. The grounding points shall be evenly arranged along the perimeter of the tank, and the spacing between down conductors shall not exceed 18m. The impulse grounding resistance of each down conductor shall not exceed 10Ω.
-
GB 50257-2014 Code for Construction and Acceptance of Electrical Installations in Explosive and Fire Hazardous Environments
7.2.1.6 For storage tanks with a volume of 50m³ or more, there shall be no fewer than 2 grounding points, with a spacing of no more than 30m. They shall be symmetrically connected to the grounding body around the bottom of the tank, and the grounding body shall form a closed loop.
