Grounding System Design for Anti-static Work Areas
Anti-static work areas (EPAs) are important electrostatic protection zones. Below, we mainly introduce how the electrostatic grounding system within an EPA is designed.
Discharging static electricity to the ground is a primary method for eliminating static electricity. To ensure rapid, safe, and effective discharge, an anti-static grounding system should be installed.
EPAs often contain single-phase electronic equipment with unbalanced currents. Furthermore, the presence of fluorescent lamps, thyristors, and other non-linear loads in the environment generates high-order harmonics in the circuits, causing a significant current to flow through the neutral conductor. TN-S or TN-C-S power supply grounding systems have a dedicated, non-energized protective earth (PE) conductor, thus providing better safety.
EPAs inevitably contain various electronic devices and equipment. Therefore, in addition to the common lightning protection grounding, working grounding, and protective grounding systems found in general buildings, there are also DC working (signal reference grounding, logic grounding) grounding, shielding grounding, power grounding, and anti-static grounding systems. Due to their different functions, different grounding systems should not be mixed to suppress mutual interference and must adhere to the principles of overall equipotential bonding and local equipotential bonding. To ensure proper interrelationships between various grounding systems, the design of the grounding system should be based on the design of the lightning protection grounding system. Since various functional grounding systems often ultimately adopt a combined grounding method, the design of the lightning and static electricity protection system should be considered first, ensuring that other functional grounding systems are included within the protection scope of the lightning protection grounding system.
Equipotential bonding should be established between the grounding ports of the static electricity grounding system. The static electricity grounding system should be designed with a low-impedance static discharge gas path. In addition to meeting low resistance requirements, the cross-sectional area of the grounding conductor must also meet sufficient mechanical strength and other electromagnetic compatibility requirements. Electronic and aerospace industry standards stipulate that the cross-sectional area of the main grounding conductor should not be less than 95^2 mm², and this specification references this standard.
The main anti-static grounding line should generally be connected from the main equipotential bonding terminal block. When the anti-static work area is located in a high-rise building, and the vertical distance between the main equipotential bonding terminal block and the floor of the anti-static work area is large, the main anti-static grounding line should preferably be connected from the floor's equipotential bonding terminal block to ensure equipotential bonding between the anti-static grounding terminal block and other grounding equipment on the floor.
The explanation of Clause 5.2.2 of the National Standard "Technical Specification for Lightning Protection of Electronic Information Systems in Buildings" GB50343-2004 states that when equipotential bonding measures are adopted in a building, each equipotential bonding network has a reliable direct connection to the earth to the common grounding system. Each electronic system's equipotential bonding network should not have a separate grounding down conductor connected to the main equipotential bonding terminal block; instead, each equipotential bonding network should be connected to the equipotential bonding terminal block of its own floor or electrical shaft using a grounding wire.
This regulation is to ensure a good grounding connection and a low-impedance electrical path for the entire facility's grounding system. To reduce electromagnetic interference coupling, the shielding metal layer of the grounding cable should be grounded at both ends.