Wiring
RID16
16
Hauser
4.3.3
Maximum spur length
The line between the distribution box and field device is described as a spur.
In the case of non-Ex applications, the max. length of a spur depends on the number of spurs (>1
m/3.28 ft):
4.3.4
Number of field devices
In accordance with IEC 61158-2 (MBP), a maximum of 32 field devices can be connected per
fieldbus segment. However, this number is restricted under certain conditions (explosion
protection, bus power option, field device current consumption). A maximum of four field devices
can be connected to a spur.
4.3.5
Shielding and grounding
Optimum electromagnetic compatibility (EMC) of the fieldbus system can only be guaranteed if the
system components and, in particular, the lines are shielded and the shield forms as complete a
cover as possible.
• To ensure an EMC protective effect, connect the shield as often as possible to the reference
ground.
• For reasons of explosion protection, you should refrain from grounding however.
To comply with both requirements, the FOUNDATION Fieldbus™ basically allows three different
types of shielding:
• Shielding at both ends
• Shielding at one end on the feed side with capacitance connection to the field device
• Shielding at one end on the feed side
Experience shows that the best results with regard to EMC are achieved in most cases in
installations with one-sided shielding. Appropriate measures with regard to input wiring must be
taken to allow unrestricted operation when EMC interference is present. These measures have been
taken into account for this device. Operation in the event of disturbance variables as per NAMUR
NE21 is possible with one-sided shielding.
Where applicable, national installation regulations and guidelines must be observed during the
installation!
Where there are large differences in potential between the individual grounding points, only one
point of the shielding is connected directly with the reference ground. In systems without potential
equalization, therefore, cable shielding of fieldbus systems should only be grounded on one side, for
example at the fieldbus supply unit or at safety barriers,
Number of spurs
1 to 12
13 to 14
15 to 18
19 to 24
25 to 32
Max. length per spur
120 m (393 ft)
90 m (295 ft)
60 m (196 ft)
30 m (98 ft)
1 m (3.28 ft)
