Several questions regarding the power cables for control cabinets and instruments
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This post was last edited by The project’s progress on 2022-3-18 06:55. 1. The electrical power supply is of the TN-S type; should the power cables for the local control cabinets and instruments be two-core or three-core? Is there any difference in the number of core wires for the 220VAC and 24VDC power cables used to supply the instruments? Is there a difference between explosion-proof and non-explosion-proof environments? I understand that the extra conductor is PE, used for protective grounding. So, is it feasible to connect a wire directly to the nearest ground plane on site? 2. Are there any requirements regarding running the 24VDC power cable for the instruments and the 220VAC power cable for the local cabinet in the same tray?
Just casually mentioned: 3-core, with the PE end having a metal casing and the other end connected to ground； It is best to use separate cable trays for 24V and 220V; if that’s not possible, partitions should be used……
I would like to ask if there are any specific requirements regarding the pattern when laying them separately; what criteria should be used to make the adjustments to the drawings?
There are regulations specifying that the analog signals from the instruments and the DC24V supply at the instrument site must be separated; if they are to run in the same conduit, a partition must be placed in between
In the TN-S system, it is required that the N and PE wires on the source side (isolation transformer/UPS) be combined and grounded together at that side. N is the alternating-current working point, where there is loop current in the circuit, whereas the PE wire normally has no loop current. Three-core cable, L/N/PE, is supplied from the electrical supply to the instrument distribution cabinet. Due to the operating current, the voltage of the N terminal on the instrument side with respect to ground is higher than that of the PE terminal. The PE of the cabinet should also be grounded repeatedly, ultimately connected to the electrical grounding system. The on-site equipment 220 is powered using 3-core wires, with the PE wire connected to the grounding terminal inside the equipment. Enclosure grounding is considered redundant grounding, but on-site grounding is required in explosion-proof areas.
I checked the SH and HG specifications, and both state that the AC power supply lines for instruments should be laid separately from the instrument signal lines; there is no mention of separating 220V AC from 24V DC……