What are the requirements for thermistor wiring for the EMX3? The manual has all the necessary information but does not elaborate in some areas. I have listed below my interpretation, would appreciate if you guys could provide some comment, thanks.
1) Our cable length from the starter to the motor is 500m. The thermistor's trip level is 3600 kOhm (pretty standard) - so for three PTC thermistors in series, each with a trip level of 250ohm (again pretty standard). So based on some elementary calculations we could run 500m of 1.5mm2 cable to the thermistors without trouble.
2) The EMX3 manual states 'the thermistor circuit should be run in screened cable'.
a) Is this to protect the thermistor reading? or to prevent noise being coupled into the starter control circuit?
Is screened cable really necessary? Radiated noise from the bypassed soft starter motor and cable should be very low, but the run is quite long, the motor and thermistor cables will be parallel probably with their sheaths touching. If it was a VSD, or even a non-bypassed starter, I would not argue, but this seems overkill in the case of a bypassed soft starter.
c) If we run in unscreened cable is there anything we can do to filter noise from the thermistor input? Is there galvanic isolation on the EMX3 thermistor input?