Motor-Driven Appliances (Mixer-Grinder, Fan, Washing Machine, Water Pump)
What this domain tests
Motor-Driven Appliances covers mixer-grinder, fan, washing machine and water pump. The exam checks motor types, starting capacitors, speed control, mechanical load, water systems and electrical safety.
Core rules
- A mixer-grinder usually uses a universal motor with brushes and a commutator; worn brushes cause sparking, noise and loss of power. Speed control is often a triac circuit.
- A ceiling fan uses a permanent-split capacitor motor. A failed capacitor is a common cause of humming without rotation. Replace it with the same capacitance and a voltage rating equal to or higher than the original.
- A washing machine may have an inlet valve, pressure switch, motor capacitor, drain pump, timer or PCB. A water pump is usually a centrifugal pump; it must be primed, must not run dry, and needs a correctly rated capacitor and overload protection.
- Discharge capacitors before testing. Check bearings, couplings, impellers and filters as well as electrical parts.
Worked example
A ceiling fan hums but the blades do not turn. With the fan isolated and the capacitor discharged, a capacitance meter reads open circuit instead of about 2.25 µF. Reasoning: the start/run capacitor has failed, so the motor has no rotating field. Fit a capacitor of the same capacitance and adequate voltage rating, check that the shaft turns freely, then test run current. If the winding is open, replace the fan.
Traps that cost marks
Fitting a capacitor with the wrong µF value; using a low-voltage capacitor; not discharging before test; reversing a pump motor by random rewiring; and running a pump dry while looking for an electrical fault.