Requirements for the number of conductors in the instrument power cable
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I would like to ask everyone: for the cable that supplies power to the instruments separately (as well as the solenoid valves), is it necessary to use a 3-core cable, or can a 2-core cable be used? Are there any regulatory requirements? 24V DC using 2x2.5mm2? 220V AC, 3x2.5mm2?
24V devices usually have only two terminals for connection; even if you use a three-core cable, it won’t work. At 220V, there is usually an additional PE conductor; of course, the grounding method depends on the design of the specific system. It may not come from the power supply cabinet, but rather from a nearby grounding point, in which case it is not a three-core cable.
Could you explain the design of a three-core PE grounding system? Or could you recommend any materials or standards? Thank you~
Find out the differences between TN-C, TN-S, TN-C-S, TT, etc
AC220V requires PE grounding protection, so it is generally three-core; DC24V can do with two cores. Article 3.1.3 of HG/T20513-2014 \"Code for Grounding Design of Instrument Systems\": Field instruments, transmitters, local switches, etc., powered by voltages below 36V do not require protective grounding unless there is a specific need for it. Article 10.2.2 of GB50093-2013 \"Code for Construction and Quality Acceptance of Automatic Instrumentation Projects\": For on-site instrument switches and similar devices with a supply voltage not exceeding 36V, protection grounding is not required unless specified otherwise in the design documents.