Bulletin No. 3020IM9503R6/98 Power Meter
December 1998 Chapter 6—Communications
1998 Square D All Rights Reserved 41
LENGTH OF THE COMMUNICATIONS LINK (POWERLOGIC, MODBUS, OR JBUS)
The length of the communications link cannot exceed 10,000 feet (3,048 m).
This means that the total length of the communications cable from the PNIM,
personal computer, or PLC, to the last device in the daisychain, cannot exceed
10,000 feet. The maximum distance may be shorter, depending on the baud
rate. Table 6-1 shows the maximum distances at different baud rates.
DAISYCHAINING PM&CS DEVICES (POWERLOGIC, MODBUS, OR JBUS)
Note: To daisychain the power meter with other PM&CS, Modbus, or Jbus devices, use
a communications cable containing two twisted-shielded pairs (Belden 8723 or
equivalent). Strip back the cable sheath 2" (51 mm) on each end of the cable, and strip
back the insulation 0.25" (6 mm) from the end of each wire. Then follow daisychaining
instructions in this section. Torque terminal block screws to 5–7 lb-in (0.56–0.79 N•m).
Each communicating power meter has a 5-position plug-in RS-485 terminal
block for connection to a PM&CS, Modbus, or Jbus communications link. On
all PM&CS devices, the terminals are labeled IN+, IN-, OUT+, OUT-, and
SHLD. On the power meter, the IN+, IN-, OUT+, OUT-, and SHLD terminals
are numbered 5, 4, 3, 2, and 1, respectively.
To daisychain a power meter to another PM&CS, Modbus, or Jbus device,
wire the power meter’s RS-485 communications terminals to the matching
communications terminals of the next device (wire the IN+ terminal of the
power meter to the IN+ terminal of the next device, wire IN- to IN-, OUT+ to
OUT+, OUT- to OUT-, and SHLD to SHLD). See figure 6-5.
If the power meter is the last device on the daisychain, use a terminator at the
end of the link. See Terminating the Communications Link in this chapter
for instructions. If the power meter is the first device on the daisychain,
connect it to the PNIM, personal computer, or programmable controller using
a CAB-107 or equivalent cable and a Multipoint Communications Adapter.
See Biasing the Communications Link in this chapter for instructions. See
Appendix C for the CAB-107 pinout.
Note: See Appendix H for 2-wire Modbus and Jbus wiring distance limits.
Baud
Maximum Distances
Rate
1–16 devices 17–32 devices
1200 10,000 ft. (3,048 m) 10,000 ft. (3,048 m)
2400 10,000 ft. (3,048 m) 5,000 ft. (1,524 m)
4800 10,000 ft. (3,048 m) 5,000 ft. (1,524 m)
9600 10,000 ft. (3,048 m) 4,000 ft. (1,219 m)
19200 5,080 ft. (1,548 m) 2,500 ft. (762 m)
Table 6-1
Maximum Distances of Comms Link at Different Baud Rates
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