Issue
Can existing communication wiring from a NETWORK 8000 (ASD) or DMS (MicroSmart) system be reused for a BACnet MS/TP trunk?
Product Line
TAC IA SeriesEnvironment
- NETWORK 8000 (ASD) cable
- DMS (MicroSmart) cable
- BACnet MS/TP
Cause
ASD and MicroSmart cables were designed for lower baud rates. BACnet MS/TP networks often require higher speeds, which these cables may not reliably support beyond 9600 or 19200 baud, especially over extended distances.
Resolution
-
Reuse Conditions:
- ASD and MicroSmart wiring can be reused for BACnet MS/TP only at 9600 baud, and possibly 19200 baud under limited conditions.
- For higher baud rates or longer cable runs, replace with BACnet-compliant cable.
-
Recommended Cable Specifications for BACnet MS/TP:
- Type: Shielded twisted pair
- Gauge: 18 AWG or 22 AWG
- Impedance: 100–120 Ω
- Capacitance: ≤ 30 pF/ft (98 pF/m)
- Maximum Length:
- 9600 baud: up to 1200 m (4000 ft)
- 38400 baud: up to 1200 m (4000 ft) with proper cable
- Examples: Belden 3105A, 3106A or equivalent
-
Ensure proper network biasing and termination when reusing existing wiring.
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If communication issues persist, migrate to recommended cabling standards for BACnet MS/TP.
Cable Specification Comparison
| Parameter | ASD / MicroSmart Typical Cable | BACnet MS/TP Recommended Cable |
|---|---|---|
| Type | Unshielded or basic twisted pair | Shielded twisted pair |
| Gauge | 22–24 AWG | 18–22 AWG |
| Impedance | ~70–90 Ω | 100–120 Ω |
| Capacitance | ~50 pF/ft (164 pF/m) | ≤ 30 pF/ft (98 pF/m) |
| Shielding | Often none | Foil or braided shield |
| Max Segment Length | Designed for ASD baud rates | 1200 m (4000 ft) at 9600–38400 baud |
| Examples | Legacy ASD/DMS cable | Belden 3105A, 3106A or equivalent |
