The DCS is grounded separately; how should the instrument enclosure be grounded?
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The DCS system has its own grounding piles; the grounding of equipment that is not part of the system cannot be connected to this grounding. The lightning protection and electrical systems are grounded together. So, if the enclosures of my field transmitters and other instruments must be grounded, do they need to be connected to the DCS grounding electrode? In this way, during thunderstorms, the signal wires will be at the same potential as the enclosures, eliminating any potential difference and thus preventing damage to the electronic components. If connected to the lightning protection ground, and if the lightning protection ground is not at the same potential as the DCS ground, the equipment will be damaged. Is this correct?
Generally, grounding one end is sufficient
DCS systems generally do not require separate grounding piles; they can be connected to the electrical grounding system, as long as the grounding resistance is less than 4 ohms. However, note that the access point should not be too close to the lightning protection grounding point; a distance of at least 10 meters is required, and the greater the distance, the better if conditions permit.
If the enclosures of instruments such as field transmitters must be grounded, do not connect them to the DCS grounding electrode; it is better to ground the DCS separately
Regarding grounding, there are already many discussions and examples on the forum; full-length equipotential bonding is used far more often than separate grounding installations for electrical and instrumentation purposes. The regulations require that the enclosures of field instruments be grounded only when the voltage used is above 36 V; if you really need to ground yours, then use lightning protection grounding. It’s not easy to connect the DCS grounding terminal to the device! !
At present, our company adopts the following measures for instrument grounding: 1. When instruments are connected to the DCS, single-end grounding is used, that is, the cable shielding layer is grounded to the DCS working ground electrode. 2. The protective grounding and the working grounding of the DCS are separated and connected to their respective grounding busbars. 3. After the protective grounding and the working grounding busbars are combined into one common grounding busbar, this busbar is connected either to the individual grounding of the instruments or to the plant’s ground electrode. 4. It is ensured that the total instrument grounding resistance is less than 0.4 ohms
For the grounding of the transmitter enclosure, a value of <100Ω is sufficient.