Watlow CLS - Manual (Page 30)

22 CLS User’s Guide
Installation
Thermocouple Wiring
Use 18 or 20 AWG thermocouple (T/C) extension wire for all the T/C
inputs.
NOTE
Most thermocouple wire is solid unshielded wire. Use
shielded wire if required at your installation; ground one
end only.
WARNING
The CLS uses a floating ground system. Therefore:
Isolate input devices or host computers connected through
communications cables (like RS-232) from earth ground.
Use ungrounded thermocouples with the thermocouple
sheath electrically connected to earth ground.
Use optically isolated RS-232 devices to isolate earth
grounded host computers from CLSs.
When you use grounded T/Cs, tie the thermocouple shields
to a common earth ground in one place. Otherwise any
common mode voltages that exceed 5 volts may cause
incorrect readings or damage to the controller.
WARNING
The 16CLS has single ended inputs, offering little protec-
tion from common mode voltage sources. Therefore
Watlow Anafaze highly recommends that you use
ungrounded thermocouples with the external thermocou-
ple sheath electrically connected to earth ground.
You can use 400 to 500' of thermocouple extension wire, depending on
wire type and wire size, and keep to accuracy and source impedance
specifications. Be sure to install thermocouple wiring in a separate
conduit away from AC power (the 120 Vac control supply) and high
power (240 Vac or higher) wiring.
Input Wiring
Use multicolored stranded shielded cable for analog inputs. Watlow
Anafaze recommends that you use #20 AWG wire. (If the sensor
manufacturer requires it, you can also use #22 or #24 AWG wiring.)
Most inputs use a shielded twisted pair; some require a 3 wire input.