Control room grounding selection

Considering the mutual influence, it’s the same in theory.

The current standard requires equipotential grounding, which is what the original poster meant by “drawing from a mesh grounding system”; there are requirements regarding the grounding resistance

Let me tell you, there’s actually no difference; it’s just an additional parallel ground connection. Remember, no matter how many ground connections you make, they all need to be connected together in the end. So if the factory’s grounding network meets the requirements, try not to create separate ground connections – it’s a waste.

In my understanding, mesh grounding may cause interference due to different potentials at various points; for control systems in control rooms where high performance is required, it is best to use separate grounding.

This post was last edited by hfrs on 2016-1-19 at 20:55. A potential difference can only occur with a separate grounding, which in turn can interfere with the system. It is also not allowed by the regulations.

Most of the engineering projects I have come across and about which I have information suggest a mesh grounding system to ensure equal potential throughout the entire plant; however, special attention must be paid to the connection points for instruments – for example, the grounding point for DCS systems should be placed far away from the building’s lightning protection grounding system.

:So why does the DCS control panel of Zhejiang Zhongkong need to be grounded separately? Their installation staff said it cannot be connected to the main power grounding system

　　Within the area of mesh grounding, the potential difference between different grounding electrodes is small, resulting in low contact voltage and step voltage for humans. Interference between different grounding methods is also low; for example, in areas with mesh grounding and in areas without it, when signals are grounded at multiple points, the consequences in areas with mesh grounding are much less severe than those in areas without such grounding. 　　However, the potential distribution outside the mesh grounding area remains uneven, and the step voltage there is still very high. Especially in areas near the mesh ground, the potential difference between different grounding electrodes is relatively larger. The greater the area of the grounding grid, the more pronounced this effect is. 　　If the control room is located within a mesh grounding system, using a grounding busbar drawn from this mesh grounding system as the grounding for the control system yields better results than creating a separate grounding system. 　　If the control room is located outside the area covered by the mesh grounding system, and a grounding busbar is drawn from the mesh grounding system for the grounding of the control system, then a potential difference may exist between the ground and the surrounding environment (such as the building). By using an independent ground, this potential difference can be reduced. 　　I’m not quite sure about the specific requirements. It seems that the control room is above the device’s grounding grid, and using a mesh grounding system is fine ； 　　The control room is not above the grounding grid and has its own grounding system; for the grounding of the control system, some connections are made from the mesh grounding system, while others use a separate grounding method. I’m not sure exactly what the considerations are; according to the electrical specialist, it’s fine to use a grounding grid with an area of three to fifty square meters for a shed located about twenty to thirty meters away.

You’re right; I couldn’t find any national standards regarding the grounding distance, but I generally agree that a distance of more than 15 meters is sufficient for lightning protection grounding.