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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 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) 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 of the drive 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.
The motor overload protection supports thermal memory retention and speed
sensitivity.
For more information, see drive firmware manual.
Implementing a motor temperature sensor connection
WARNING!
IEC 61800-5-1 requires double or reinforced insulation between live parts
and accessible parts when:
• the accessible parts are not conductive, or
• the accessible parts are conductive, but not connected to the protective
earth.
Obey this requirement when you plan the connection of the motor
temperature sensor to the drive.
80 Guidelines for planning the electrical installation
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