User manual

eElectro Industries/GaugeTech Doc # E113-7-03-1.18 1-7
1.4: RS485 Wiring Details1.4: RS485 Wiring Details
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RS485 communication allows multiple devices to communicate on a bus. The Substation
Multiplexor’s Slave Port 1 and Port 2 are 2-wire RS485 terminals, viable for a distance of up to 4000
feet (1219 m).
• Use a shielded, twisted pair cable, AWG 22 (0.33 square mm) or larger.
• Establish point-to-point configurations for each device on a RS485 bus: Connect (+) terminals to
(+) terminals; connect (-) terminals to (-) terminals.
• Protect cables from sources of electrical noise.
• Avoid both “star” and “tee” connections (see diagrams on the following pages). No more than
two cables should be connected at any one point on an RS485 network, whether the connections
are for devices, converters or terminal strips.
• Include all segments when calculating the total cable length of a network. If you are not using an
RS485 repeater, the maximum length for cable connecting all devices is 4000 feet (1219 meters).
• Connect devices using the diagrams on the following pages. A correct connection requires 1/4
watt resistors connected to the (+) and (-) terminals of each device at the end of a straight-line
bus. The line impedance of the cable and the resistor should match. Generally, a 100- or
120-Ohm resistor will work.