Doc# E107706 5 - 11
5: Communication Wiring
Electro Industries/GaugeTech
The Leader In Power Monitoring and Smart Grid Solutions
Electro Industries/GaugeTech
The Leader In Power Monitoring and Smart Grid Solutions
5.6.1: RS485 Connection—Nexus® Meter to Nexus® I/O Modules
• Six feet of RS485 cable harness is supplied. Insert one end of the cable into Port 3
or Port 4 of the Nexus® 1250/1252 meter.
• Insert the other end of the cable into the I/O module’s female RS485 side port (see
Figure 5.8). The connectors fit only one way into the ports.
• Use the male RS485 side port to attach another I/O module. The Nexus® 1250/
1252 meter can power up to four connected I/O modules using 15–20V DC at 50–
200mA. Use the steps in Section 5.6.2 to determine if you must use a separate
power source (for example, EIG’s PSIO) to supply added power to the group. See
Section 9.2.1 for information on the PSIO. RS485 communication is viable for up to
4000 feet (1219 meters). However, if your cable length exceeds 200 feet, use the
remote power supply and:
1. Connect the + and - terminals on the Nexus® meter to the + and - terminals of
the female RS485 port. Connect the shield to the shield (S) terminal. The (S)
terminal on the Nexus® meter is used to reference the meter’s port to the same
potential as the source. It is not an earth-ground connection. You must also
connect the shield to earth-ground at one point. Vous devez également
connecter l’écran à la terre à un moment donné.
2. Provide termination resistors at each end, connected to the + and - lines. RT is
approximately 120 Ohms. See RT EXPLANATION in Section 5.3
5.6.2: Steps to Determine Power Needed
Available power for all ports of the Nexus® 1250/1252 meter is 12 VA.
1. Refer to the tables on the next two pages to determine the VA Ratings for I/O
modules and displays.
2. Add together the VA Ratings for all I/O modules and displays in use.
3. Compare available power to power needed to determine if you must use an
additional power source.
NOTE: EIG recommends the PSIO 12V power source if the I/O module VA rating
exceeds the Nexus® specification. See Section 9.2.1 for information and usage
instructions.
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