BACnet MS/TP Communication Data Bus Fundamentals
Network Guide 25
Figure 8: Typical Cable-Shield Grounding Requirements for a BACnet MS/TP Data Bus Segment with a Building
Controller located in the Middle of the Data Bus
Figure 9: Typical Cable-Shield Grounding Requirements for a BACnet MS/TP Data Bus Segment without a
Building Controller
ECB-PTU Line-Powered Data Bus Controller Shield Grounding
Requirements
The shield on each data bus segment must be connected to the electrical system ground at
one point only, for example, at the Data Bus Master (Building Controller) if there is one, as
shown below in Figure 10 and Figure 12. On data bus segments without a Data Bus Master,
the ideal point to ground the shield is in the middle of the data bus segment as shown in Figure
13.
Figure 10: Typical Cable-Shield Grounding Requirements for a BACnet MS/TP Data Bus Segment with a Building
Controller located in the End of the Data Bus
Typical BACnet 24VAC-
Powered Controller
Data Bus Shield:
Isolate with
electrical tape
Data Bus Shields: Twist
together and Isolate
with electrical tape
Typical BACnet 24VAC-
Powered Controller
Typical BACnet 24VAC-
Powered Controller
Data Bus: Shielded Twisted Pair Cable
NET+
NET-
NET+
NET-
NET+
NET-
Bus Master (Building Controller)
Typical EC-BOS Device
+ -S
Typical BACnet 24VAC-
Powered Controller
NET+
NET-
Data Bus Shield:
Isolate with
electrical tape
Data Bus Shields:
Connect to the ‘S’
terminal
Electrical
System
Ground
The shield of the data bus must be connected to
the electrical system ground at one point only –
usually at the Building Controller , when present
Data Bus Shields: Twist
together and Isolate
with electrical tape
Typical BACnet 24VAC-
Powered Controller
Data Bus Shield:
Isolate with
electrical tape
Typical BACnet 24VAC-
Powered Controller
Data Bus Shields: Twist
together and Isolate
with electrical tape
Typical BACnet 24VAC-
Powered Controller
Data Bus Shields: Twist
together and Isolate
with electrical tape
Typical BACnet 24VAC-
Powered Controller
Data Bus: Shielded Twisted Pair Cable
NET+
NET-
NET+
NET-
NET+
NET-
NET+
NET-
Typical BACnet 24VAC-
Powered Controller
NET+
NET-
Data Bus Shield:
Isolate with
electrical tape
Electrical
System
Ground
The shield of the data bus must be connected to
the electrical system ground at one point only,
ideally in the middle of the data bus as shown
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