GE Industrial Solutions POWER LEADER PMCS Network Architecture Guide - Manual (Page 26)

Power Management Control System
Chapter 2 – Network Design
16
5. Each RS-485 network must have its shield properly
grounded. Figure 9 illustrates proper RS-485 wiring
and grounding.
CAUTION: Improper grounding may create a
ground-loop condition and cause
communications failures. Make sure you follow
the wiring diagram carefully.
To ensure proper grounding, follow this procedure.
Begin by grounding the RS-485 cable shield at the
host. Follow the cable to the first IED on the
network. Do NOT connect the cable ground to the
IED. Pick up the RS-485 output cable from the IED
and attach its ground to the IED’s shield connection
or grounding screw. For IEDs with no grounding
connectors, connect to earth ground.
Follow the cable to the next IED, and repeat the
above procedure. Do not connect the RS-485 shield
from the previous IED, but DO connect the RS-485
OUT shield on its way to the next IED.
EXCEPTION: The Multilin 565 Feeder
Management Relay does not have isolated
communications ports. Do NOT connect the
shield at this IED. Instead connect the shield of
the incoming RS-485 cable to the shield of the
outgoing RS-485 cable, skipping the Multilin 565.
Rules of thumb : RS-485 cable ground should always be
connected at the previous IED, never upon arrival at
an IED. All RS-485 IEDs must have either two
communications cables attached or one
communications cable and a terminating resistor.
RS-485 Host
(RS-485 card*, RS232/RS-485 converter,
Multiple Serial Port or Ethernet Gateway RS-485 port)
Network Connections: + - Shield
RS-485 IED #1
Shield
+
-
RS-485 IED #2
Shield
+
-
Two wire, twisted,
shielded pair cable
RS-485
RS-485 IED #31
Shield
+
-
120-ohm
terminating resistor
Shield
connected
at host
Shield not
connected
at first IED
RS-485 IN
Shield
connected
at first IED
RS-485 OUT
Shield not
connected
at IED
RS-485 IN
Shield
connected
at IED
RS-485 OUT
Shield not
connected
at IED
RS-485 IN
120-ohm terminating resistor
* Connect Tech RS-485 cards
require a 600-ohm resistor
in place of the 120-ohm
terminating resistor.
Figure 9. Network illustrating Modbus Rules 4 and 5.
6. A single RS-485 network may have up to 215
commnet IEDs attached to it via POWER LEADER
Modbus Concentrators. Figure 10 illustrates this
rule.