Instrument grounding system
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I would like to ask everyone: (1) According to the latest specifications for instrument installation, should the instrument grounding system be connected to the grounding system of low-voltage electrical equipment? If that is the case, how are the working ground and protective ground of the DCS system connected to the low-voltage electrical ground? (II) Additionally, according to standard 10.4.7 of the petrochemical instrumentation construction standards, the outer shielding layer of split-screen shielded cables, as well as the protective metal layer of armored cables, must be connected to protective grounding at both the site and the control room/cabinet room. As per 10.4.9, the shielding layer of the cables at the field instrument equipment side should be left ungrounded and insulated. The shielding layer of the same circuit should maintain reliable electrical continuity; it should not be left floating or grounded repeatedly. The shielding layer of armored cables should be grounded together with the instrumentation equipment. Are there any conflicts? (III) In previous years, wasn’t it required that the grounding of DCS systems be separate and not connected to the electrical ground? If I remember correctly, in a DCS cabinet, the working ground and the protective ground are eventually connected together and fed into a single ground, right?
(1) According to the latest specifications for instrument installation, the instrument grounding system usually needs to be connected to the grounding system of low-voltage electrical systems. The working ground and protective ground in the DCS system should be connected to the low-voltage electrical grounding point through separate grounding wires, to ensure the safety and reliability of the entire system. (II) Regarding the grounding of shielded cables and armored cables, although the two regulations may seem to conflict, they actually apply to different situations. Clause 10.4.7 states that grounding at both ends is required to prevent circulating currents, while clause 10.4.9 specifies that the shielding layer of the cables at the field instrument equipment end should be left ungrounded, in order to avoid grounding loop problems caused by too many grounding points. As long as the electrical continuity of the shielding layer is ensured and the armor layer is properly grounded, these two requirements can coexist. (III) Early DCS systems typically require separate grounding to avoid potential interference with the electrical ground. However, with advances in technology and standards, it is now preferred to combine the working ground and the protective ground and connect them to the electrical ground, provided that the grounding system is designed properly to avoid circuit or noise issues. It is recommended to consult the latest relevant specifications to obtain specific guidance for implementation. .
Thank you for your patient explanation! I would also like to ask: According to the latest regulations, for a DCS system, should two separate grounding wires be used for the protective ground and the working ground, both of which are connected to the electrical neutral ground?