Danfoss VLT DMS 300 Manual page 66

See section Galvonic Isolation (PELV) for further details.
Advanced motor protection
The FCD 300 Series has integral electronic
motor protection.
The variable frequency drive calculates the motor
temperature on the basis of current, frequency and time.
As opposed to traditional, bimetallic protection,
electronic protection takes account of reduced cooling
at low frequencies because of reduced fan speed
(motors with internal fan). This function cannot protect
the individual motors when motors are connected in
parallel. Thermal motor protection can be compared
to a protective motor switch, CTI.
To give the motor maximum protection against
overheating when it is covered or blocked, or if the fan
should fail, you can install a thermistor and connect it
to the variable frequency drive's thermistor input (Digital
input), see parameter 128 Thermal motor protection.
NOTE
This function cannot protect the individual
motors in the case of motors linked in parallel.
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Decentral Solutions
MG.90.F2.22 - VLT is a registered Danfoss trademark