Meter Engineers Handbook for Cellular Communication 14
4.5  ABB/Elster Alpha Power Plus Meters
Identical to Elster A3 Meters in section 5.1. Requires optional RS-485 communications board.
4.6  AMETEC Power Instruments JEMStar Meters
Requires the optional RS-485 board. Half Duplex (two wire) RS-485 only. 120 ohm termination resistor is not 
required at the Digi TransPort WR21 end of the cable. The Digi TransPort WR21 has an internal termination resistor 
that is soware selectable. It is necessary at the meter end.
RS-485 Output Connections Switchboard RS-485 Output Connections
Color Signal
Terminal Signal
Wht/Grn/Blu XMT/RCV -
21
XMT/RCV -
Wht/Grn/Blu XMT/RCV +
22
XMT/RCV +
For Switchboard style meters, the connections are provided on terminal blocks.
JEMStar Digital Multifunction Electricity Meter User Manual.  Pub: 1083-600 Rev S. Pgs. 50, 55