The Importance of Anti-Static Grounding
Below, I will introduce several common concepts regarding grounding:
A. Protective Grounding: This involves establishing a secure metallic connection between the non-current-carrying metal parts of electrical equipment and a grounding electrode (grounding system).
B. Functional (System) Grounding: This refers to the direct connection-or connection via specialized equipment (such as arc-suppression coils, impedances, or resistors)-of a specific point in an electrical power system (typically the neutral point) to the earth.
C. Repeated Grounding (Parallel Grounding): By maintaining a very low grounding resistance, this method ensures that if a phase conductor comes into contact with the metal enclosure of a device downstream from a break in the neutral (zero) line, the voltage of that enclosure relative to the earth remains minimal, thereby significantly reducing the risk of electric shock to personnel.
D. Lightning Protection Grounding: This type of grounding is designed to rapidly conduct lightning currents into the earth to prevent damage from lightning strikes.
E. Anti-Static Grounding: This involves creating an electrical path to the earth for objects that carry static electricity or are capable of generating it (provided they are not insulators). The resistance for anti-static grounding is generally required to be no greater than 10 ohms.
(2) Relationship Between Anti-Static Grounding and Other Types of Grounding
In anti-static engineering, there are two common methods for installing ground lines within an electrostatic protected area (EPA). The first involves installing a dedicated, independent grounding system and routing the ground line to the specific anti-static workstations on the production line. The second method utilizes the ground line from a three-phase, five-wire power supply system; in this setup, a separate earth-ground line is routed alongside the neutral (zero) line to serve as a grounding bus for anti-static purposes.
Anti-static grounding should, whenever possible, avoid sharing a grounding electrode with the grounding systems used for precision instruments. This is because the discharge of static electricity can sometimes generate high-amplitude pulses, which may interfere with the operation of such instruments.
Anti-static ESD grounding must be kept separate from lightning protection grounding. When lightning protection grounding discharges lightning current, it can generate a high back-strike voltage; if this voltage is introduced into an electrostatic protection zone via an electrostatic grounding system, it may lead to safety incidents or damage to instruments and equipment. In engineering practice, electrostatic grounding should be kept at a distance of 20 meters from lightning protection grounding.