Process Signal Wire Size
Process Signal Wire Size
(OP)
Can anyone suggest a recognized standard (ISA, IEEE,...) that provides information on sizing 4-20mA process control wire? I am specifically looking for a recommended maximum voltage drop for the wire using a 24VDC, two conductor circuit.
Regards,
GaDawg
Regards,
GaDawg





RE: Process Signal Wire Size
RE: Process Signal Wire Size
You may find short distances within a DCS cabinet between 18-22 AWG. Home run cables from the marshaling cabinet to junctin boxes may be 16 AWG. Individual instrument runs to the JB may also be around 16 AWG.
Several ISA standards mention conductor gauges for various applications. Examples include 12.06.01 for IS wiring, 50.02 part 2 for Foundation Fieldbus, etc.
RE: Process Signal Wire Size
xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Process Signal Wire Size
GaDawg
RE: Process Signal Wire Size
Through the courtesy of Ohm's law, R=v/i=12/0.020=600 total ohms. The receiver device typically has about 125 ohms impedance. That leaves 475 ohms. So you can select whatever wire you want that will give you less than 475 ohms in the distance you need to run it. It takes a long run of wire to make that much resistance. Most instrument loops use vast overkill in selecting wire that will carry 20 amps instead of 20 milliamps.
RE: Process Signal Wire Size
For single twisted pair cable, we generally specify a minimum size of #16 AWG. For multi-pair cable, we specify #18 AWG.
RE: Process Signal Wire Size