How To Install; The Bacnet Interface - Danfoss Native BACnet VLT HVAC Drive Operating Instructions Manual

How to Install

3 How to Install

3.1 The BACnet Interface

3.1.1 Cabling
Cable lengths and number of nodes
For the correct function of a BACnet MS/TP system, it is mandatory to fulfill installation of the communication cables given in
this manual. Under correct installation it is possible to have up to 250 nodes (125 masters and 125 slaves) on 1200 meter (4000
feet) cable.
The use of drop cable connection (i.e. T-connection) is not allowed in a BACnet MS/TP system. Drop cables will lead to reflection
and malfunction of the system. In location where the cabling will demand a T-connection the use of repeaters is recommended.
Note that a repeater is a node in both of the two segments it connects. The number of frequency converters is based on a single
master system. If there are two or more devices (e.g. PC tools, Routers), the number of frequency converters must be reduced
correspondingly.
- Maximum length of an MS/TP segment: 1200 meters (4000 feet)
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Characteristic impedance: 100 to 130Ω
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Resistance: <110Ω/km
- Distributed capacitance: <100pF/m, between conductors
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Cross section: 0.82mm
- Cable type: twisted in pairs, 1 x 2, or 2 x 2 wires
- Screening: Copper-braided screen or braided screen and foil screen
Use of the same cable type throughout the entire segment is recommended to avoid impedance mismatch.
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VLT HVAC Drive Native BACnet Operating Instructions
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conductor area, corresponding to AWG 18
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MG.14.C1.02 - VLT is a registered Danfoss trademark
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