In what situations is it appropriate to use an on-site terminal box?
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When designing control systems, should the control cables be connected directly from the field instruments to the DCS, or should they first be connected from the field instruments to local terminal boxes, with multi-core cables then being used to lead them to the DCS terminal blocks?
Isn’t it done through the local bus technology to the control room now?
If there are few instrument panels, they can be connected directly to the secondary instruments. Since DCS is used, there are certainly many instruments, and they are generally connected through junction boxes.
The function of the on-site junction box is to branch or combine wires/cables; in addition, it provides a testing point for on-site instruments. In situations where there are multiple instruments at a certain location on site, it is advisable to use on-site junction boxes to branch or combine cables. Additionally, if the instruments are installed on equipment, it is recommended to use on-site junction boxes to monitor them without having to climb up onto the equipment.
What was said on the 4th floor is correct – the function of the on-site junction box is not only to provide a point for instrument monitoring; it also offers significant advantages when additional instruments need to be added or when wires need to be replaced, as it reduces the amount of work required.
If it is the client’s instrumentation personnel, multi-core cables are not recommended. Just having so many intermediate connectors, that is, failure points, is a huge problem. Approximately one-third of trips caused by general instruments are due to loose terminals. Is it scary? The additional cost of one jump has already been recovered. How dare there be so many terminals in the middle?