Regarding the selection of cable trays for instruments
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This post was last edited by The project’s progress on 2024-8-7 07:01. We have a boiler room project abroad, and the general contractor has purchased the materials based on the list provided by the electrical control manufacturer. For analog instrument cables, RVVP is used, while RVV is used for digital signals. The cable trays used are open-type ladder-type cable trays. In our design, according to the standards, instrument signal cables should be computer cables, whereas digital signals from motors and valves require shielded cables. The cable trays used are covered slot-type trays; the selection of cables is primarily based on considerations related to interference resistance. Chemical industry standards specify the use of covered cable trays, but nothing is mentioned regarding ladder-type or slot-type trays. I’m not sure whether covered cable trays are also chosen for the purpose of reducing interference. These materials have now been purchased and shipped onto the ship. The project requires that we use these materials for drawing, with no changes allowed. I also consulted the electrical control manufacturer regarding the selection of cables, and they said that this is the standard approach they use, so there should be no issues. I think the only thing we can do is ensure proper grounding during construction, and avoid laying the cables near electrical cable trays. But for the tray-type cable trays that don’t have covers, I originally thought that having covers would serve not only to reduce interference but also as a form of protection for the cables. This project is located in Africa, in an outdoor environment; I’m not sure if using cable trays without covers could lead to other problems
When selecting cable trays for instruments, several key factors need to be considered for the uncovered ladder-type cable trays used in your project: 1. **Interference resistance requirements:** Generally, to reduce electromagnetic interference, it is recommended to use shielded cables for instrument signal cables, along with cable trays that have covers. Covered cable trays provide additional protection, preventing cables from being affected by external electromagnetic interference and ensuring the accuracy and stability of signal transmission. 2. **Environmental factors:** You mentioned that the project is located in Africa and is set up outdoors; therefore, special attention must be paid to the material of the cable trays and their protection rating. The outdoor environment may pose greater risks of physical damage (such as storms, rain erosion, ultraviolet radiation, etc.), and cable trays without covers may not be able to adequately protect the cables from these factors. 3. **Installation and Maintenance:** Trunking with covers provides better protection during maintenance and repair, preventing damage to the cables during these tasks. At the same time, in areas with a lot of dust or animal activity, covered cable trays can better prevent contamination and animals from biting the cables. Given these factors, I recommend considering a reevaluation of the use of covered trough-type cable trays in your project, especially for the transmission of critical instrument signals, to enhance the reliability and security of the system. If it is necessary to use the materials that have already been purchased due to cost or other reasons, it is recommended to take additional protective measures for the cables in critical areas, such as adding local shielding or using cables with a higher protection rating. It is worth noting that before implementation, local standards and regulatory requirements should also be taken into account to ensure that the selection of all equipment and materials complies with local regulations. .
1. Ladder racks are used mainly due to their good heat dissipation properties, which make them suitable for power cables. From this perspective, not having a cover is beneficial for heat dissipation. 2. The design of the cover plate takes into account the following 5 aspects: ① electrical interference, ② dust, ③ high temperatures and splashes of corrosive chemicals, ④ mechanical damage, ⑤ direct sunlight. When electrical interference needs to be blocked, a pore-free metal tray with a solid cover plate should be used ； In areas with flammable dust, each layer of cable tray should be equipped with a solid cover ； Areas prone to dust accumulation should be equipped with covers ； Measures should be taken to handle high temperatures and prevent chemical liquids from splashing. It is advisable to use empty pallets, with a solid cover plate on each layer ； Measures to prevent mechanical damage should be taken. Except when laid in a distribution room or shaft, vertical cables below 1.8 m in length shall be provided with protective measures. When the horizontal laying height is too low, it also needs to be considered. (Civilian: 2.2m, Petrochemical: 2.5m) Measures should be taken to protect against direct sunlight. (At least the top cable tray should be covered with a plate.)
Well, I’ve included the suggestions you gave in the construction requirements. The materials themselves can’t be changed, so I’ve asked them to take additional measures to prevent direct sunlight exposure and mechanical damage