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Start-up 4-9MN894
Circuit Breaker is Tripping − During Starting
If the shunt trip light comes “ON” during starting it may detect a weak input phase.
This is typical of grounded delta and open delta power systems. For proper
operation, a four wire WYE system is recommended.
If the shunt trip light is ON and it is determined that input power is correct and there
is a motor load; Then, disable the shunt trip circuit and do an SCR resistance test.
1. If the result of the SCR test shows the SCRE’s are in good condition, try
restarting. If the shunt trip light comes ON again, check the line voltage for a
weak phase.
2. If the SCR’s test bad, find out why they failed.
SCR’s fail due to high voltage. Is there a capacitor bank or a contactor in the
circuit? Check MOV’s and line voltage. MOV’s may be shorted or open due to
clearing of previous voltage spike.
SCR’s fail due to high current or high temperature.
a. Check the “T” leads for a phase to phase and phase to ground short
circuit.
b. Check the motor winding.
c. Check the voltage balance of power supply. If one leg is going to 25 - 30%
of nominal voltage or less during starting this will create high current on the
other phases.
d. Make sure the cooling fans are working and the ambient temperature is
within specification.
All Baldor starters are tested under load before shipping for proper SCR
performance.
OC light Comes ON Shutting “OFF” The Starter
1. If it trips during starting it may mean that S2-5 (CL) needs to be set to “ON”. If it
is already ON, be sure there are no capacitors or shorts in the motor leads.
2. If it trips when the Ramp End light comes ON, make sure that S2-2 (CM) is
“OFF” or current monitor level is set properly for a given load.
3. The control will turn OFF any time motor current exceeds 450% of the S1
current calibration setting.