Regarding the issue with instrument trays

HGT 20509-2014 \"Code for Design of Instrument Power Supply\" includes provisions for the calculation of instrument power supply capacity. The method of laying cables separately often causes difficulties. In fact, the purpose of laying cables separately is to prevent interference and prevent energy transfer between intrinsically safe and non-intrinsically safe systems. In accordance with this requirement and taking the on-site conditions into account, in most cases it is sufficient to separate the 220V wires from other wires, or to separate intrinsically safe wires from those that are not intrinsically safe. For the remaining few special cases, a small amount of armored wire (or shielded wire) will suffice. The “armoring” of armored cables can serve as a partitioning barrier. At the same time, armored cables are well-protected and are less likely to experience external leakage of electricity, so it doesn’t matter whether they are intrinsically safe or not ； Optical cables are not energized and are not affected by electromagnetic interference, so they can be installed freely. However, it is usually placed on the low-voltage side.

It depends on who is responsible for the 220VAC power cable – the electrical department or the instrumentation department.

Q1: Is it the instrument’s responsibility to handle the 220V power supply cable, or is it the electrical department’s responsibility? A1: Please refer to HGT20636.2-2017, Chapter 4, on the division of design tasks between the automation team and the electrical team. Theoretically, the division of labor is as such, but in practice, if these instrument wires originate from the DCS power distribution cabinet (UPS) for automatic control, they are all designed by the automatic control team itself. It is recommended to consult with the design institute and the electrical engineering team to determine which department should be responsible for producing the drawings. Q2: For non-intrinsic safety applications, does an AC power supply signal require two partitions? A2: Signal cables with different levels and voltage ratings should be separated; as for how to do this, different cable trays can be used, or partitions can be added to the same cable tray. It is recommended to follow the overall plan; if it is a main cable tray on the utility tunnel, it is advised to use different types of cable trays. Q3: Can armored cables and optical fibers be laid together? A3: This mainly applies to the laying of optical fibers. When a cable is armored, it is equivalent to having a metal sleeve added to it; in such cases, the optical fiber can be placed inside the ordinary cable (in fact, dual-shielded cables have a similar nature to armored cables)

The power supply for on-site instruments is designed by the instrumentation team; the cables within the cable trays should be separated into active and passive types, as well as between intrinsically safe and non-intrinsically safe systems

In practice, it is uncommon for intrinsically safe and non-intrinsically safe cables to be laid separately; however, 220V power cables and signal cables are indeed laid separately.

The power supply must be kept separate from instrument wires, control wires, etc. If it’s all one control unit, or the wires on one long screen are connected through one trunking, there is no problem.

Thank you, I’m here to learn from all of you experts.

Generally, an instrument tray can be divided into three sections: for power cables, intrinsically safe cables, and non-intrinsically safe cables. Optical cables are not affected by interference and can be placed anywhere