Insulation issues with cabinets and cable trays

An additional note on specification SH 3521 for trough boxes is attached; how should this sentence be understood?

I’m here to address the zero-replies issue~ For these two questions, the standards indeed don’t provide explicit guidelines, but it’s possible to arrive at the answers easily through logical analysis. 1. Does the DCS cabinet need to be insulated from the steel foundation? First, you need to understand what the purpose of insulation is here The DCS cabinet is a device that operates under electrical voltage. In accordance with grounding requirements, it needs to be grounded both for operational purposes and for protection purposes. You don’t seem to understand the concept of insulation here – is it meant to prevent electric shock or interference? 2. Insulation is certainly not required between the cable trays and supports on the pipe rack, because according to the instrument grounding standards, the cable trays need to be bonded together and grounded at multiple points. These grounding points can be dedicated grounding electrodes, or the supports and the frame structures of the pipe rack can be used for grounding; this grounding serves the purpose of providing shielding against interference. Therefore, from the perspective of grounding purposes and principles, the insulation option is never chosen.

I don’t think it’s necessary to use insulating pads for the two issues I mentioned, but the client insists on their use, which I find unreasonable; I’m looking for a basis for this requirement.

Mm. . . The first question indeed doesn’t state it clearly; it only says that the enclosure needs to be grounded, so in theory insulation is not required. The second question is explicitly specified in HG20513

If insulation pads (or other measures) are required to isolate the cable trays on the pipe rack between aluminum alloy and carbon steel supports, this is explicitly stipulated in standard 50093, in order to prevent electrochemical corrosion.

In GB 50093 - 2002: 5.2.5 When dashboards, cabinets, and control panels are installed in vibrating environments, vibration prevention measures shall be taken in accordance with the requirements of the design documents. The rubber pads placed between the DCS cabinets in the cabinet room and the steel frames serve as vibration prevention measures, not insulation measures. According to 9.2.1 of GB 50093 - 2002: 9.2.1 All normally non-electrified metal parts of electrical measuring instruments, such as enclosures, instrument bases, cabinets, boxes, cable trays, protective devices, brackets, and bases, which may acquire dangerous voltages due to insulation failure, shall be provided with protective grounding. For local instruments, switches, etc. with a supply voltage not exceeding 36V, protection grounding is not required unless specified otherwise in the design documents. The DCS cabinets in the cabinet room shall be grounded in accordance with this clause.

I feel like it’s all about the same issue, namely the protective grounding of instruments. I feel that the chemical industry standards provide more detailed explanations than the national standards!

1 The rubber pad for the cabinet is included, as are the bolts – ordinary stainless steel bolts. (The owner can raise objections and show the manufacturer’s delivery instructions; that’s how Zhejiang University Zhongkong does it.) Insulating pads are to be placed on the bridge frames – I’ve really never seen that done before; it’s too complicated for construction purposes. As for corrosion, over time, or in an environment with many corrosive gases, it is inevitable. As the owner, I didn’t ask the construction party to do this, which delayed the progress.

I think it’s crazy to try to use insulation; plus, chemical corrosion – compared to the importance of protective grounding, chemical corrosion is completely insignificant.

Everything is grounded, so what’s the point of insulation?