The fieldbus specifications recommend that new fieldbus Type A cable be used whenever possible. The standard fieldbus Type A cable provides a maximum distance of 1900 meters for a single segment. Before using any other type of cable, verify the cable characteristics to determine its suitability and the maximum distances associated with its use.
When upgrading a system to fieldbus devices, you can use existing instrument wiring such as multi-conductor cable if you require a significantly reduced cable length. Where it is required, we recommend at a minimum the use of Type B cable which has multiple twisted pairs with an overall shield. This type still provides reasonable distance at 1200 meters. Since the DeltaV Controller and I/O can be remotely mounted, there should be minimal need for the multi-conductor cables. Use new fieldbus Type A cable for all trunk portions of the segment, and use existing field wiring only for spurs of short length.
For new and upgrade installations, Emerson highly recommends only new fieldbus Type A cable for the trunk and spurs.