Why does a star delta motor run at a very slow speed on delta after changing from star to delta?
There could be several different reasons for a motor to run slower than it should do after it has been switched over from star to delta connection.Here are some possible reasons, but there may be others:its star-delta starter unit has a fault or has some bad external connectionsa broken or disconnected phase winding (or windings) inside the motor's frame.As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.Before you do any work yourself,on electrical circuits, equipment or appliances,always use a test meter to ensure the circuit is, in fact, de-energized.IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOBSAFELY AND COMPETENTLYREFER THIS WORK TO QUALIFIED PROFESSIONALS.