Belden EIA-485 Cables Provide Superior Electrical Performance in Plenum Environments – Without the Use of Conduit
EIA-485 (formerly RS-485 or RS485) is an OSI model physical layer electrical specification of a two-wire,  half-duplex, multipoint serial connection. The standard specifies a differential form of signaling. The difference between the wires’ voltages is what conveys the data. One polarity of voltage indicates a logic 1 level, the reverse polarity indicates a logic 0 level. The difference of potential must be at least 0.2 volts for valid operation, but any applied voltages between +12V and -7V will allow correct operation of the receiver.
Using a EIA-485 physical interface, the maximum distance achieved would be 4,000 ft. at 100kbps. A maximum of 247 nodes is possible.