￭ 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 using an external overload device
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) and the common UL\IEC 61800-5-1 standard in
conjunction with UL/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 UL/IEC 60947-4-1 and NEMA
ICS 2.
Guidelines for planning the electrical installation 79
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