12
Protection and Monitoring
Safety Manual
MN042004EN March 2017 www.eaton.com
Protection and Monitoring
Motor Thermal Overload
The Overload function models the thermal characteristics of a
motor and generates a Fault Trip event that de-energizes the
motor before motor damage will occur. This is intended to protect
the motor and power wiring from excessive current. Trip curves
are defined by applicable agency standards. The trip class for
any particular Overload class is user adjustable. When the FLA
is entered for the motor, the thermal capacity value will be cal-
culated to model the motor temperature during motor operation.
Thermal capacity can be characterized by the calculated value rep-
resenting the relative position with regard to the Trip Class curve.
For example; a motor running at a thermal capacity value of 85%
is much closer to an Overload Fault Trip than the same motor run-
ning at a thermal capacity value of 25%.
The following items are associated with the electronic Overload
function of the C445.
•
An Overload Fault Trip will occur when the calculated thermal
capacity reaches 100%.
•
An Overload Fault Trip cannot be cleared by power cycling the
device – the thermal capacity calculated value is stored in non-
volatile memory.
•
Two thermal capacity models are used. One model is enabled
while the coil is energized (motor is running) and a sec-
ond model is enabled while the coil is de-energized (motor
stopped). The second model has a longer time constant.
•
A MANUAL RESET button is located on the faceplate of the
unit. Depressing this button will clear any Overload fault that
has been latched, but is no longer present (thermal capacity
must be less than 100%). Resets can also be initiated through
the communication port.
•
An auto-reset option is available. This provision enables the unit
to automatically reset when the fault has cleared.
CAUTION
In the Auto Reset mode, caution must be exercised to assure
that any restart occurs in a safe manner. Auto Reset mode
should not be used in environments where excessive restart
attempts may cause component damage and/or create unsafe
conditions.
Overload Curve
The thermal overload is designed to protect the motor from over-
heating caused by excessive current. If the motor is overloaded,
the current level may rise above motor FLA and heats the motor.
The FLA sets the trip threshold and the trip class (5 to 40) is set
with Overload Trip Class.
The trip class settings of the C445 motor management relay are
suitable for both normal start-ups as well as for heavy duty start-
ing. The Trip Class setting enables a particular tripping characteris-
tic to be selected.
The thermal memory and the reset inhibit time are saved to the
non-volatile memory. Cycling power on the device will NOT clear
the thermal Fault Trip nor reset the thermal capacity stored in
non-volatile memory. These values are reloaded when the device
boots and the timer is restarted at the full reset time. This means
if the 3 minute inhibit timer has been running for two minutes,
cycling power will require the user to wait the full three min-
utes before a reset can clear the overload fault.
Overload Trip Curve ( -40C to 60C )
