Is there a specific specification in which the cable cross-section for 2-wire 24VDC instruments used in DCS/PLC is defined?
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I would like to ask everyone: Is there any specification that specifies the cross-sectional area of the cable for 24VDC two-wire instruments used in DCS/PLC systems? Generally, KVVP cable with a cross-sectional area of 1.5 square millimeters is used, but I haven’t delved into to find out exactly where the relevant specifications can be found. My idea is that there are specific regulations for 4-wire systems: the signal cable can use a gauge of 1.0 to 1.5, while the cable used for powering the instruments should have a gauge of at least 1.5. From this, it can be inferred that 2-wire systems should also use cables with a gauge of at least 1.5
It can be roughly estimated using the load capacity of the two-wire system. In the operation manuals of standard two-wire instruments, there is a diagram showing the relationship between the supply voltage and the circuit load; calculations can be done using this diagram. When selecting the wire gauge for the circuit, ensure that the circuit resistance does not exceed the specified value.
The wire area can be determined using the wire resistance and the allowable voltage drop in the circuit. It is generally not less than 1.5 mm2.
Our requirement is 1.5mm
The same standard is sought; the instrumentation industry is quite arbitrary, unlike the electrical engineering field which has strict standard requirements – there is always a basis for everything, and this industry is highly mature
The Code for Electrical Design in Explosive Atmospheres GB50058 specifies the minimum wire diameter for cables in such areas; the design codes for instrument piping and wiring also address wire diameters. You can check these out – PDF versions of the codes are available on forums
It depends on the industry, distance, and many other factors; regulations don’t cover everything.