Domestic Appliances and Their Repair
This domain tests the construction, operation and fault diagnosis of domestic appliances such as electric irons, heaters, fans, mixers, refrigerators and washing machines. The exam expects logical fault finding: supply, switch, fuse, thermostat, heating element, capacitor, motor and wiring.
Core rules
- A heating appliance converts electrical energy to heat. Its element has a definite resistance; an open element gives no heat and reads infinite resistance.
- A thermostat opens and closes the circuit to hold temperature. If it is stuck open, the appliance stays cold; if stuck closed, overheating may occur.
- A capacitor-start fan motor may hum but not start if the capacitor is faulty. Discharge the capacitor before testing.
- Refrigerators and washing machines have motors, controls and safety interlocks. Always isolate before removing covers.
- Test insulation resistance after repair and confirm earthing before returning an appliance to service.
Worked example
A 1,000 W, 230 V iron does not heat. Its expected element resistance is R = V²/P = 52,900/1000 = 52.9 Ω. A meter reads infinity across the element terminals. The supply and switch test normal, so the element is open-circuit and must be replaced. A reading near 0 Ω would suggest a short circuit instead.
Traps
Do not test resistance on a live appliance. Do not assume the thermostat is faulty before checking the element and supply. Do not touch capacitor terminals without discharging. Do not return an appliance with a defective earth.