【2026 Grounding Systems】Differences between instrument grounding, electrical grounding, and lightning protection grounding
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Instrument grounding, electrical grounding, and lightning protection grounding are three common types of grounding in industrial and building electrical systems. Although all serve the purpose of ensuring safety and system stability, they differ in function, application scenarios, and regulatory requirements. Mixing may cause safety hazards or equipment failures.
I. Definitions and Key Differences of the Three Concepts Instrument grounding: It is primarily used for signal reference and noise suppression, to ensure the stability of signals in automated instruments and control systems such as DCS and PLC. According to SH/T 3081-2019, instrument grounding includes: protective grounding (safety grounding): to prevent the metal enclosure from becoming charged. Working ground (signal ground): Provides a stable reference potential for the signal circuit. Shield grounding: to suppress electromagnetic interference. Anti-static grounding: Prevents the accumulation of static electricity. Intrinsically safe grounding (required only for Zener safety barriers).
Electrical grounding: Refers to the grounding system in electrical power systems that is implemented to ensure the safety of people and equipment. It mainly includes protective grounding: connecting the metal casing of equipment to ground in order to prevent electric shock caused by leakage current. Working ground: Such as the grounding of the transformer neutral point, to maintain system voltage stability. Repeated grounding: Multiple points of grounding for the neutral wire in TN systems to enhance the reliability of protection.
Lightning protection grounding: Specifically used to quickly conduct lightning current into the ground, thereby protecting buildings and equipment from damage caused by lightning strikes. This is achieved by connecting lightning arresters such as lightning rods and lightning strips to a dedicated grounding system.
Note: Common grounding refers to the situation where all grounding systems share the same grounding grid, in which case the total grounding resistance must be ≤ 1Ω.
III. Prohibitions and Risks of Mixing Groundings Prohibited scenarios: Connecting lightning protection grounding directly in parallel with instrument/electrical grounding. Lightning currents can be extremely high (tens of thousands of amperes), and if the impedance of the common path is insufficient, it may lead to high-voltage backfeed, which can destroy sensitive electronic equipment. Mixing of protective earth (PE) and working earth (N): This violates standards such as GB 50054, and may result in the equipment enclosure becoming charged. Mixing of instrument signal ground with high-voltage ground: introduces power-frequency interference, affecting control accuracy.
Conditions for shared use: All grounding systems share a single grounding electrode, with a total grounding resistance of ≤1Ω (combined grounding). The instrumentation system is connected to the electrical grounding system through an equipotential bonding network to avoid potential differences.
IV. Recommendations for proper practices: Separate installation – It is advisable to use separate grounding electrodes for lightning protection, keeping a distance of ≥3 meters from the grounding electrodes used for electrical and instrumentation purposes (unless combined grounding is employed).
Equipotential bonding: All grounds are connected to a common ground plate, forming an equipotential body to eliminate potential differences.
Independent grounding wire: The instrument grounding should be connected to the grounding bus using a separate grounding wire; series connection is prohibited.