Tstat8 Wiring Topology

I will be trialing a few of the Temco Bacnet/Modbus controllers and programmable thermostats for commercial HVAC applications. Tstats8’s may be used for Fancoil and VAV Box Control and Monitoring over Bacnet MS/TP. The T3-XB’s with T3-IO’s may reside on TCP/IP Ethernet Networks, for AHU Control, Monitoring and Trending of (All) connected Analog Inputs.

My typical (Standard) RS485 bus topology supports 32 (Daisy Chained) devices between “EIA-485 Repeaters” on a single bus of approximately 1200 meters length with 18 AWG twisted shielded cable, 3 repeaters increase the total to 128 devices with a maximum RS485 bus length of approximately 2800 meters (3 repeaters with four segments).

My questions are;

  1. What is the recommended topology for Temco Tstat7’s, Tstat8’s, Tstat9’s, Tstat10’s to T3-XB, T3-Nano or USB-RS485 Gateways/ Controllers/Converters
  2. Are separate end of line termination resistors (EOL, 120 Ohm, 1/4, watt 5%) required on the 485 Bus.
  3. What are the recommended maximum quantity of Tstat8’s per T3-XB’s and T3-Nano’s.
  4. What are the maximum quantity of T3-XB’s, T3-IO’s and T3-Nano’s per each Ethernet Bus

I would like to create a similar wiring topology diagram (for my use), but have not seen / found any info on “Quantity of devices” in the Temco Controls Documentation. Thanks.

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Will have to ask my team to look up the details but in general we have sites with hundreds of devices per 485 bus. I usually don’t put more than 50 devices or so to keep the cabling more manageable. If you run into trouble you can always add a repeater, the OR485 and t3-nano both can operate as optically isolated repeaters.

Termination resistors are optional.

Will add more details from the rs485 chip data sheets shortly, specifically the device loading info.

Thanks for the prompt reply.
I received my trial Temco tstats and controllers today, thanks.

I am setting up a test / demo board with the devices and sensors. The info would be valuable for submittal data if the client initially accepts the lack of UL and FCC listings (UL 916 and FCC Part 15). Bacnet / Modbus is the selling point due to existing Honeywell (Legacy), Siemens, Johnson (Legacy) and recently KMC DDC Bacnet devices. Looking forward to any additional info.

Yes, the approvals are coming. What we have so far us there on the various product pages. I can add FCC soon. BTL is under way.

Maurice Duteau

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Thanks, the FCC and BTL would be helpful, looking forward to any additional info…

A possible “Work-Around” for the UL listing of the T3-X controllers could be installing them in NEMA1 or Nema12 UL Listed Electrical Panel Enclosures…

  1. http://www.kele.com/Catalog/06%20Enclosures/PDFs/NSTA%20Series%20Catalog%20Page.pdf
  2. http://www.kele.com/Catalog/06%20Enclosures/PDFs/RP%20Series%20Catalog%20Page.pdf

But here it depends on written approvals from the Institutions and Architects / Mechanical Engineers…

A preliminary topology diagram…

Technically speaking, the controlllers are classified as “low voltage” devices. Anything under 40v, as long as it’s powered by a UL listed class 2 (which means it’s energy limiting or fused) transformer then the electrical inspector will not give you a hard time.

I realize owners and the specifying engineers ask for UL though so we are in the middle of getting UL on a number of items.

Maurice Duteau

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