Max FF spur length is 120 m. However one of the Shell DEP says: "The maximum spur length shall be 200 m. The spur length is the length of the cable from the device coupler to the FOUNDATION Fieldbus device. While un-terminated spur lengths up to 200 m are allowed, any spur over 100 m requires the Principal's approval."
What does this mean? As per FF standard, spurs cannot be more than 120m. Is it possible for spurs to be more than 120m?
What is the max spur length in case of IS devices?