RKI Instruments M2A - Manual (Page 27)

M2A Transmitter Operator’s Manual 22
The number of cables or wires needed will depend on whether the M2A is wired to a gas
monitoring controller or just to power, whether any relays are used, and whether the Modbus
output is used.
NOTE: If the M2A is being wired to a PLC or DCS device, see “Appendix B: PLC and DCS
Device Wiring” on page 66, then continue with step 8.
Use the following recommendations to determine how to wire the M2A:
• If Modbus connections will not be used and only the PWR/SIG connections will be used,
use a two or three conductor shielded cable or two or three wires in conduit for
connections to the power/signal terminal strip depending on whether or not the signal (S)
terminal is used. The S terminal has a 4 - 20 mA output, but if you do not need to monitor
this signal and do not connect to the S terminal to access this signal, the M2A will still
function completely.
• If the PWR/SIG connections and one or more relays are used, route the connections to the
M2A in conduit. Use shielded cable in the conduit for the PWR/SIG connections and
unshielded cable or individual wires for the relay connections. Make sure any wire or
cable used for relay wiring is appropriately rated for the power that it will carry.
NOTE: If shielded cable is used for the PWR/SIG connections, leave the cable shield’s drain
wire insulated and disconnected at the M2A. You will connect the opposite end of the
cable’s drain wire at the controller or device.
• If the M2A will be wired into a Modbus network, see “Chapter 8: RS-485 Modbus
Output” on page 51.
Table 4: Wire Size for PWR/SIG Connections
Max Distance to Controller
w/18 Gauge Wire
Max Distance to Controller w/
16 Gauge Wire
Max Distance to Controller
w/14 Gauge Wire
2,500 ft. 5,000 ft. 8,000 ft.