Cable Specs:

  • 22 AWG with (1) Twisted Pair + 1 Conductor Shielded
  • Plenum rated where required
  • Impedence of between 100 and 130 ohms
  • Capacitance between conductors of less than 30 pF per foot (100 pF per meter).
  • Capacitance between conductors and shield less than 60 pF per foot (200 pF per meter)

Installation Requirements

  • Trunks may be up to 1000 ft., but 500 ft. or less is recommended.
  • Check specifications on max device count per trunk.  In general, we recommend no more than 32 per trunk.
  • Repeaters are not recommended.
  • 120 OHM resistor at each end of the trunk across the receiver (+ and - terminals).  Do not terminate resistor in third (ground) wire or on shield.
  • Butt splice shield/drain at each location
  • Butt splice and tape common reference/ground where common terminal is not available
  • Ground shield/drain at one end only.
  • RS-485 is polarity sensitive. 
  • Ungrounded end of the drain must be wrapped with at least 4 rotations around cable casing and taped with 2 wraps.  Do not cut the drain short in the casing.
  • Must be wired in point-to-point daisy chain fashion.  No T-taps, stubs, spurs, or stars.
  • May not share conduit with 120v+ cabling.



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