How to interface Induction motor thermistor with ATV28 VFD.

Dear all,
I am driving 11kW induction motor from Schneider Altivar ATV28 VFD.
My 11 kW motor is equipped with thermistor but i am unable to utilize it.
I need to know how to connect and configure this thermistor, so that the VFD will trip on actual rating of motor.
Following are the model numbers of motor and VFD,

INDUCTION MOTOR 11 kW, 1475 rpm:
Make: Siemens
Type: 1AV3162B
Ordering Code: 1LE10031DB234AB4
Power: 11kw
Current: 20.5A
Voltage: 400V
Speed: 1475 rpm
Frequency: 50 Hz

Variable Frequency Drive Data:
Make: Schneider
Model: ATV28HD23N4S303
Input Frequency: 50 Hz
Output Frequency: 0.5 to 400 Hz
Input Current: 40A
Output Current: 33A
Power: 15kW

You will need a thermistor relay from Schneider - these have contact outputs.

You have 4 digital inputs on that drive (called Logical Inputs, LI). LI1 is the run-stop command and cannot be reprogrammed, but if you are not using one of the other three, you can program one of them as "nSt", which is an immediate coast to stop, energy is removed from the motor, any Decel command is ignored. The way that works is that once an LI is programmed for that, it must be High for the drive to run. Wire that up to the thermistor in the motor and when the motor temperature exceeds the thermistor threshold, the resistance goes almost infinite, which the drive LI will interpret as Open and shut the output off. This is the same thing that an external thermistor relay will do for you.

Jraef,
Are motor thermistors always ptc? (resistance goes up with temperature)

Thanks Jraef,

g.mccormick said:

Jraef,
Are motor thermistors always ptc? (resistance goes up with temperature)

Click to expand...

I can't answer to always, but I have never seen an NTC thermistor used in a motor, and every thermistor trip relay I've ever used had no option for working from an NTC. A PTC makes the logic for it more "logical" in that there is no problem with a motor being too cool (with reason). So having the resistance rise with temperature makes it fail safe, in that if a wire breaks, the resistance goes infinite and trips. It also allows it to be easily used in series with an emergency stop button with a NC contact.