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Discuss Thermistor protection in 3 phase star wired motor in the Electrical Forum area at ElectriciansForums.net

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NICK C SPARKS

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Hi all just installing a 3 p extractor fan and in the instructions which are in broken english it says it needs thermistor protection would this just be wired back to the dol starter and wired in line with the contactor circiut ai through the thermsitor relay( which i presume is normanly closed) them to the motor and back to a2 cotactor terminal
cheers
 
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K

Knobhead

  • Thread Starter Thread Starter
  • #2
The two leads from the thermistor wire direct to the relay. The relay will have both NO/NC contacts that you can wire in to the DOL starter to suit you.
 
Actually, it depends on the thermistor. Some go open circuit when a certain temperature is reached and some are resistive that change resistance with temperature and need a special thermistor relay that has to be reset.

To be honest, I rarely see them connected at all (especially in fans as by their very nature they blow cool air over themselves) As long as the overload is set exactly right - they'll trip if a problem occurs.
 

Pete999

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The fan won't be blowing cool air over the motor, the fan is being used in an extraction situation the air will more than likely be very warm and humid
 

DPG

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I think he's sorted it now. He's had 4 years :) Daz
 
hahaha. The thread showed up below in the similar thread thingy.... I didn't check dates. :)

Ah well, it might help anyone reading later.
 

DPG

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Yeah the similar thread thing has caught me out before!
 
S

spary

  • Thread Starter Thread Starter
  • #8
I'll just add that thermistors must be used on motors running in hazardous areas that are using speed control
 
K

Knobhead

  • Thread Starter Thread Starter
  • #9
Actually, it depends on the thermistor. Some go open circuit when a certain temperature is reached and some are resistive that change resistance with temperature and need a special thermistor relay that has to be reset.

To be honest, I rarely see them connected at all (especially in fans as by their very nature they blow cool air over themselves) As long as the overload is set exactly right - they'll trip if a problem occurs.

You are talking of thermal fuses not thermistors. They are only used in small cheap motors.


Thermistors and thermocouples are embedded in the windings of many large motor to protect the huge investment companies sink in to them.
 

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