MANUAL MOTOR STARTER GUIDE
APRIL 19 7/80
The greatest risk for applications such as motors is over-
heating. Abnormal temperature rises can be caused by
overloads, electrical faults, cooling problems or improper
operating parameters or operation conditions. This differ-
entiates motors and pumps from other applications, such as
heating resistors or lamps.
Examples of such overloads include:
Overloads caused by over current
– locked rotors
– long starting or braking times
– changes of the friction ratio of the operated engine
– non-permissible intermittent operations
– long-term overloads in continuous operation
– undervoltage
Supply problems, which could cause unsymmetrical over-currents
– earth faults
– phase loss
– phase unbalance on the supply side
– interwinding or interturn fault within the motor
Cooling problems
– reduced convection currents due to dust or dirt
– mounting position of the motor: good circulation of air prevents heat build-up
– low air density due to incorrect installation and altitude environmental parameters
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