Fault Finding – Single Phase Motors & Standard Controllers

ProblemPossible Cause
‘ACO” (and ‘MCO’) Does not Close when Start is Called for.Fault with supply. Power supply absent at terminals L1, L2 and N. External control circuit is blocking operation. Thermal Overload ‘T.O.L.’ is tripped. Control fuse ‘CF1’ is blown. ‘ACO’ coil is open circuit. Controller wiring is faulty. Electronic switch ‘SC’ is faulty.
‘ACO’ Closes But ‘MCO’ Does Not.‘MCO’ coil is faulty. Controller wiring is faulty.
‘ACO’ and ‘MCO’ Close but Motor Fails to Rotate.Supply fuse for L2 is blown. Wiring between motor and controller faulty. Power supply drop excessive during start due to site conditions. Power supply drop increased due to faulty line capacitors ‘CL’.
(controllers 11kW and above only) Faulty start capacitors ‘CS’. Mechanical load is excessive Controller wiring is faulty. Motor winding is faulty.
Supply Fuse(s) Blow When Motor Attempts to Start.Supply fuses are undersized. Faulty line capacitors ‘CL’ (controllers 11kW and above only). Faulty start capacitors ‘CS’. Faulty run capacitors ‘CR’. Controller wiring is faulty. Motor winding is faulty.
Overload ‘T.O.L. Trips During Run-Up‘T.O.L.’ setting is incorrect. Motor taking too long to start due to adverse mechanical load and/or supply voltage. Faulty start capacitors ‘CS’. Faulty line capacitors ‘CL’ (controllers 11kW and above only). ‘T.O.L.’ is faulty.
Overload ‘T.O.L.’ Trips During Running.‘T.O.L.’ setting is incorrect. Mechanical load is excessive. Supply voltage is too low during running. Faulty run capacitors ‘CR’. ‘T.O.L.’ is faulty.
Motor Stalls When ‘ACO’ Opens After Run-Up.Mechanical load is excessive. Faulty run capacitors ‘CR’. Controller wiring is faulty. Electronic switch ‘SC’ is faulty. Motor winding is faulty.
‘ACO’ Does Not Open When Motor up to Speed.Supply voltage not equal each side of neutral. ‘ACO’ is stuck closed. Faulty start capacitors ‘CS’. Controller wiring is faulty. Electronic switch is faulty.
Fault Finding – 1-Phase Motors & Standard Controllers
Speed Control Unit

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