Cable requirements for FOUNDATION fieldbus are different from 4-20mA networks. That's why we have many kinds of cable that have been tested and registered by the Fieldbus Foundation. Jim Cahill over at Emerson Process Experts blog actually has a great post regarding a conversation that was going on in the Fieldbus Foundation LinkedIn group, where users were discussing cable requirements.
This goes into interesting territory because there is always the ongoing debate among solution providers and end users as to whether or not existing cable can be used in a retrofit fieldbus project. Existing cable can be used in some circumstances, but you have to watch out for inductance, capacitance, and resistance.
Read Jim Cahill's Blog Post Here
Read the LinkedIn Discussion Here