Implementing motor and motor cable short-circuit and
thermal overload protection
￭ Protecting the motor and motor cable in short-circuits
The drive protects the motor cable and motor in a short-circuit situation when the motor
cable is sized according to the nominal current of the drive. No additional protection devices
are needed.
￭ Protecting the motor cables against thermal overload
The drive protects the motor cables against thermal overload when the cables are sized
according to the nominal output current of the drive. No additional thermal protection devices
are needed.
WARNING!
If the drive is connected to multiple motors, use a separate circuit breaker or fuses
for protecting each motor cable and motor against overload. The overload protection
of the drive is tuned for the total motor load. It may not detect an overload in one
motor circuit only.
￭ Protecting the motor against thermal overload
According to regulations, the motor must be protected against thermal overload and the
current must be switched off when overload is detected. The drive includes a motor thermal
protection function that protects the motor and switches off the current when necessary.
Depending on a drive parameter value, the function either monitors a calculated temperature
value (based on a motor thermal model) or an actual temperature indication given by motor
temperature sensors.
The motor thermal protection model supports thermal memory retention and speed sensitivity.
The user can tune the thermal model further by feeding in additional motor and load data.
The most common temperature sensor types are thermal switch (for example Klixon), PTC
or Pt100.
For more information, see the firmware manual.
￭ Protecting the motor against overload without thermal model or
temperature sensors
Motor overload protection protects the motor against overload without using motor thermal
model or temperature sensors.
Motor overload protection is required and specified by multiple standards including the US
National Electric Code (NEC), UL 508C and the common UL/IEC 61800-5-1 standard in
conjunction with IEC 60947-4-1. The standards allow for motor overload protection without
external temperature sensors.
The protection feature allows the user to specify the class of operation in the same manner
as the overload relays are specified in standards IEC 60947-4-1 and NEMA ICS 2.
The motor overload protection supports thermal memory retention and speed sensitivity.
For more information, see drive firmware manual.
Guidelines for planning the electrical installation 85
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