Issues related to lightning protection and grounding
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Today, it was found in the liquid ammonia workshop that the motor housings had been grounded. The workshop supervisor said this was done for lightning protection. This raises a question for me: if the power system uses a TN system, then both lightning protection grounding and protection grounding to prevent electric shock exist simultaneously. How is it possible for the housings to be connected to both neutral and ground in a TN system? When protecting against lightning, workshops generally use lightning rods and lightning protection strips. Can the grounding of the enclosures of energized equipment for lightning protection be combined with both grounding and protective neutral connection?
The workshop supervisor is right. It is not only for protecting against induced lightning but also for static grounding. You need to first understand your company’s TN system. TN-C? (Impossible), TN-S-C (also impossible); therefore, it can only be TN-S. Therefore, the motor enclosures in the liquid ammonia workshop must be electrically grounded. Please refer to the \"Code for Design of Low-Voltage Distribution Systems\" (GB50054), as well as the \"Code for Design of Lightning Protection in Buildings\" and the \"Code for Static Grounding\", among others.
This post was last edited by suhuoyi212 on 2009-8-4 20:24. Do electrical equipment need to be grounded against static electricity? It is only known that static grounding is required for storage tanks and pipelines to prevent high-speed flow of the medium. This is a live electrical device; grounding is done to prevent the insulation from being broken down. Also, the workshop already has lightning protection strips installed – why is it still necessary to protect against induced lightning? In TN-S systems, both the PE and N wires are grounded; since the equipment’s casing is already connected to the N wire, why is grounding needed again? Also, it’s not possible to perform grounding and neutral connection for welding machines at the same time; the principle is the same – grounding and neutral connection should not be carried out simultaneously
The enclosures of fixed equipment (towers, vessels, pumps, heat exchangers, filters, etc.) in flammable and explosive environments where there is a risk of static electricity should be grounded to prevent static discharge.
There are many measures to prevent static electricity, such as humidification, controlling flow rates, bonding, grounding, using static neutralizers, and adding antistatic agents. For example, in the pharmaceutical industry, insulating materials are used instead of metal pipes in order to control the level of metal ions in drugs. Many of the reaction vessels used in this industry are lined with enamel, and grounding isn’t effective in such cases. Unless it’s required by regulations, I don’t think grounding is necessary; after all, this goes against the principles of TN system
Motor enclosures usually have anti-static grounding points. Motor-based equipment is generally located inside factories, and as long as the factory is equipped with proper lightning protection measures, it is not necessary to install additional grounding for the motors, as the factory’s internal infrastructure already provides shielding.
According to the Code for Design of Electrical Installations in Explosive and Flammable Environments (GB50058-92), 3.5.15(2), in explosive hazardous environments, the metal enclosures of electrical equipment shall be reliably grounded. All electrical equipment in Zone 1 of explosive gas environments, as well as all electrical equipment other than lighting fixtures in Zone 2 of explosive gas environments, shall be equipped with dedicated grounding wires. If this ground wire is laid in the same protective conduit as the phase wire, it must have the same level of insulation as the phase wire. In such cases, the metal conduits and the metal sheaths of cables in explosive gas environments can only serve as auxiliary ground wires. In explosive gas environment Zone 2, lighting fixtures may use a metal piping system with a reliable electrical connection as the grounding wire; however, pipes used for transporting flammable substances cannot be utilized. The grounding main lines shall be connected to the grounding electrode in at least two different directions within the explosion-hazardous area. The grounding system for electrical equipment should be separate from the grounding system of independent lightning rods designed to protect against direct lightning strikes. It is possible to combine the grounding system with those of lightning rods installed on buildings to prevent direct lightning strikes, as well as with the grounding system designed to protect against lightning induction; in such cases, the lowest value among these resistance values shall be adopted.
Everything mentioned above is quite comprehensive; as a supplementary point, liquid ammonia is an explosive chemical, with an explosion limit of 15%-28%.
I don’t think this is for lightning protection grounding, nor do I think it’s for static electricity grounding. Generally speaking: 1. The factory already has lightning protection grounding, so there is no need to provide separate static electricity grounding for the electrical equipment inside. 2. The measure to prevent induced lightning is not to install grounding wires, but rather to achieve equipotential connection of live equipment and facilities or to install SPDs (surge protection devices). 3. This might be redundant grounding, serving as a protective grounding in case of leakage current
The grounding of the motor enclosure may be a redundant grounding measure to prevent the otherwise uncharged enclosure from becoming charged accidentally.
It’s about anti-static grounding; it’s indeed necessary.