Wiring; Signal Wire - Macurco MRS-485 User Instructions

Macurco MRS-485 Modbus RS-485 Adapter
Figure 3-2 Connection Expanded
3.4

Wiring

3.4.1

Signal Wire

A Modbus over Serial Line Cable should be shielded for best performance. The shield should be connected on
each detector at SHD terminal and connected to a ground terminal or chassis only at one end of the bus. An RS-
485-Modbus must use a balanced pair (for A & B) and a third wire (for the Common). For RS-485-Modbus, Wire
Gauge must be chosen sufficiently wide to permit the maximum length (1,000m or 3,281ft). AWG 24 is always
sufficient for the Modbus Data. Category 5 cables may operate for RS-485-Modbus, to a maximum length of 600
m 1968.5 ft. For the balanced pairs used in an RS-485-system, wire with a characteristic impedance of higher
than 100 Ohms may be preferred, especially for 19200 and higher baud rates.
REV – 1.0 [34-2900-0019-8] 9 | P a g e