Foundation Fieldbus Trunk & Spur Topology — Explained Simply
Still confused about how FF devices are connected in real plants?
This is the backbone of every Foundation Fieldbus segment 
Basic idea
One main cable = TRUNK
Multiple branches = SPURS
Devices connect through spurs
TRUNK (Main Highway)
Carries power + communication
Runs from control room → field junction box
Long distance (up to ~1900 m)
High-quality shielded cable
Think of it as the main backbone of the network
SPUR (Drop Lines)
Connect individual field devices
Short cable length (typically ≤ 120 m)
From JB to transmitter / valve
Each device gets connected through a spur
How it looks in real plant
DCS / FF Card
Trunk Cable
Fieldbus Junction Box
Multiple Spurs
Transmitters / Valves
Why this topology is powerful
Multiple devices on single cable
Reduced wiring & installation cost
Easy expansion (just add spur)
Better maintenance & troubleshooting
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Important design points
Terminators required (2 per segment)
Spur length limitations must be followed
Proper shielding & grounding is critical
Power supply with conditioner required
Simple understanding
Trunk = Main road
Spur = Street to each house (device)
If you are in instrumentation, FF is not optional… it’s essential.
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