Do I need a shielded wire for 4-20mA signal?

I have a SLC 500 PLC with NI4 analog input card. I am using two 4-20mA signal coming from an RTD transmitter. The overall length of the cable is around 20ft. I have very limited knowledge in grounding and shielding. In my understanding, voltage signals are more susceptable to interference than current signals. So I am not sure if we need a shielded cable for this signal..

Please let me know what I should do.. Any documentation on basics of grounding/shielding would be helpful too..

Thanks for your time!

I would use shielded cable. Even if you don't have interference from any other source NOW, you might in the future from a new/changed process requiring components that would interfere with non-shielded wire.

This is a good overall reference:

http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/gmc-rm001_-en-p.pdf

Download this document from mrplc.com: EMC Guide

Help with selecting shielded cables:
Chapter 2 - Cables

Advice on termination of shielding:
Chapter 2 - Wiring Rules

mgvol,

...good link...that's a handy document

Thanks for your replies.. It would definitely help me..

krk, I created a login on that site but still it doesn't let me download anything.. says

You Do Not Have Permission To Download Files In This Category

What should I do to see the files?
Thanks..

Got it.. Had to activate..