Cpu Communication Ports - GE L30 Instruction Manual

3.2 WIRING 3 HARDWARE

3.2.9 CPU COMMUNICATION PORTS

a) OVERVIEW
In addition to the faceplate RS232 port, the L30 provides a rear RS485 communication port.
The CPU modules do not require a surge ground connection.
NOTE
3
Figure 3–26: CPU MODULE COMMUNICATIONS WIRING
b) RS485 PORTS
RS485 data transmission and reception are accomplished over a single twisted pair with transmit and receive data alternat-
ing over the same two wires. Through the use of the port, continuous monitoring and control from a remote computer,
SCADA system, or PLC is possible.
To minimize errors from noise, the use of shielded twisted pair wire is recommended. Correct polarity must also be
observed. For instance, the relays must be connected with all RS485 "+" terminals connected together, and all RS485 "–"
terminals connected together. Though data is transmitted over a two-wire twisted pair, all RS485 devices require a shared
reference, or common voltage. This common voltage is implied to be a power supply common. Some systems allow the
shield (drain wire) to be used as common wire and to connect directly to the L30 COM terminal (#3); others function cor-
rectly only if the common wire is connected to the L30 COM terminal, but insulated from the shield.
3-28 L30 Line Current Differential System GE Multilin