Danfoss MCD500 softstarter: thermistor connection

Anton.N

Member
Location
NL
Hello all!
During commissioning of a switch panel, thermistor input on one of the MCD500 softstarters was short-circuited. Now it displays "thermistor trip" permanently. Is there a way to reset it or the unit is damaged permanently?
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Connect a wire between the thermistor input terminals on the starter. Thermistor circuits work by looking for the resistance to increase, which can also mean an open circuit. So by putting a jumper wire between the terminals, you are emulating a low resistance circuit, which should be interpreted by the trip unit as a cold thermistor; good to go If it still displays “Tripped”, the circuit is damaged internally and is unlikely repairable without replacing whatever control board it is in.
 

Anton.N

Member
Location
NL
Connect a wire between the thermistor input terminals on the starter. Thermistor circuits work by looking for the resistance to increase, which can also mean an open circuit. So by putting a jumper wire between the terminals, you are emulating a low resistance circuit, which should be interpreted by the trip unit as a cold thermistor; good to go If it still displays “Tripped”, the circuit is damaged internally and is unlikely repairable without replacing whatever control board it is in.
Thanks for the reply.
I connected a 100ohm resistor to thermistor input and then I was able to reset "thermistor trip" error. So probably the measuring circuit is intact. But when I disconnect thermistor input, I still get the same error. The other softstarters in this panel have exact same settings, but they don't trip when thermistor is diconnected.
 
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