motor internal therm.switch - Electrician Talk - Professional Electrical Contractors Forum

spec grade · 10-08-2009, 10:44 PM

replacing existing motors in non classified area with vfd controlled xproof motors.Does code require internal therm.switch to be wired.vfd provides overcurrent protection.I did connect but i do not believe I had to.Any thoughts?

John Valdes · 10-10-2009, 06:33 PM

If you have a thermal, use it. Just wire it into the drive stop circuit. I have seen some use it for an indicator light, so the motor does not shut down. Is it a thermistor (RTD or Thermocouple) or NC thermal switch? If it is a sensor and not a true thermal shut off, you will need to program the drive as required.

randomkiller · 10-10-2009, 08:16 PM

I would not bother with it provided the VFD is set up properly.

MDShunk · 10-10-2009, 08:43 PM

Quote:

Originally Posted by randomkiller

I would not bother with it provided the VFD is set up properly.

I agree. If the drive is setup properly and the motor overhears at some point, you might as well keep running it until it dies. The exception might be motors cooled with an external blower motor. Some plants wire them to a light for a "head's up" so they can do a planned shutdown.