Power; Network Cabling & Requirements - Delta Controls DNT-T221 Installation Manual

Delta Network Thermostat: BACstat II DNT-T221 (Rev 2.0) Installation Guide
7. If the same power source is used for more than one device, ensure that the transformer is properly sized for the
rated VA and ensure that the same polarity is observed from device to device. Each BACstat is rated for 2 VA,
not including output loading (which is 0.5 A @ 24 VAC per triac and 20 mA maximum per analog output).

Power

The DNT-T221 BACstat II requires a 24 VAC @ 4 VA power supply – not including output loading for its
internally powered triac – typically an isolated Class II transformer. More than one device – not including
DCUs or V2 products – may be connected to the same transformer, providing the transformer is properly
sized, including line losses, and polarity is observed between controllers (in regards to 24~ and GND). The
transformer must ONLY be used to provide power to other MS/TP or LINKnet devices and field devices
powered through its outputs. Auxiliary field devices (i.e., 4-20 mA devices) that don't use ½ wave
rectification must be powered separately.
Network & Cabling Requirements
To ensure network stability and reliable communications, particularly at high speeds on the RS-485 MS/TP or
LINKnet networks, it is imperative that you adhere to the following network and cabling requirements:
Item Description
Cabling For MS/TP and LINKnet networks it is recommended that you use network cabling that
matches the following specifications:
• Balanced 100 to 120 ohm nominal impedance Twisted Shielded Pair (TSP) Cable
• Nominal capacitance of 16 PF/FT or lower
• Nominal velocity of propagation of 66% or higher
Topology For MS/TP and LINKnet networks, ensure the cable is installed as a daisy-chain from one
device to the next.
• MS/TP: The maximum number of devices per MS/TP network without any repeaters is 50.
Max. Nodes
• LINKnet: The maximum number of devices per LINKnet network is 12, depending on the
Application Controller used. Refer to Appendix G in the Technical Reference Manual.
• MS/TP: A termination board must be installed at each end of each MS/TP network segment
Termination
– or two per MS/TP or LINKnet network. Ensure you do not overlook this in laying out
Boards
your network architecture and ordering product.
• LINKnet: Termination boards need not be installed for only one or two nodes.
However, install a termination board on each end of the network when there are more
than 2 nodes.
• MS/TP: A repeater (RPT-768) is not necessary unless more than 50 nodes will be installed
Repeater
on a network or you need to extend the network beyond 4000 ft (1220 m).
• LINKnet: Repeaters should not be necessary. Ensure the maximum distance is no
more than 1000 ft (300 m).
For more detailed information, including wiring, refer to the RS-485 Network Installation Guide (DOC818-11).
Page 6 of 9 Document Edition 1.5