Siemens tiastar Instruction Manual page 45

Hazardous voltage.
Will cause death or serious
personal injury.
Disconnect power before working on
this equipment.
Problem
Overload relays trip during starting or
soon after motor is up to speed.
Overload relay trips during
motor operation.
Overload relay fails to trip on
overload current.
Probable cause
Motor overloaded.
Motor being started too frequently
at close intervals.
Excessive motor acceleration time.
Low line voltage.
Motor being overloaded.
Overload relay not adjusted to motor
capabilities or sized properly.
Relay tripping mechanism jammed.
Incorrect relay or relay set incorrectly.
Current transformers with improper ratio or
with short-circuited secondary terminals.
tiastar™ Motor Control Centers Instruction Manual Troubleshooting
Corrective action
Limit starting load and running load to
motor capabilities.
Jogging and starting operations must be limited to
capabilities of the motor and control. Check starting
limitations in motor instruction manual before
repeated starts.
The starting of high inertia loads may not permit
the use of standard overload relay application.
Where accelerating time approaches 12 seconds
or more, special overload relay bypass devices and
circuits would usually be required. Contact Siemens
regarding such problems and supply complete
data on locked-rotor starting current and total
accelerating time under maximum load conditions.
Line voltage should be maintained between
- + 10% of motor nameplate voltage.
Reduce load or correct conditions
causing overload.
Adjust relay setting in accordance with instructions
for the overload relay.
Adjustment should correspond to thermal rating
and service factor. Replace overload if not sized
properly.
Replace relay.
Check relay selection and adjustment per overload
relay instructions.
Current transformers must have step-down ratio
to correspond to full load motor current and relay
selection. Protective jumpers may be provided at
current transformer secondary terminals or on
terminal block connections to guard against open
transformer secondary circuit, and jumpers must be
removed before placing equipment in operation.
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