Process Signal Wire Sizing

[GaDawg]

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

 

[sreid]

There are safety specs for industrial control wiring that call for 18 gage wire minimum.

 

[Loopee]

This is an old thread but I can't stand not adding my two cents anyway.

I can't imagine that there would be a standard for such. The sizing for signal purposes would be dependent on how much voltage you have with your power supply after all the other load drops are considered. Then what you had left to work with would let you figure how many feet of what size you could use. Knowing the length, the size limitation would follow. 20mA doesn't drop much voltage unless the length is really long. I've never needed to even consider it unless out in a wastewater treatment situation where the signal goes thousands of feet.

But.... A practical consideration that will more likely govern the minimum length is how strong the wire or cable is when pulling through conduit. The rated pull stength may be the determining consideration. We never pulled single conductors less than 16 AWG for that reason but I've gone to multiconductors in the past to give good pull strength with smaller conductors usually #18 or #20.