Domestic Electrical Appliances: Construction and Working
What the exam tests
This domain tests the construction and working of common domestic appliances: electric iron, kettle, heater, fan, mixer, refrigerator, washing machine and vacuum cleaner. Expect identification of parts and conversion of electrical energy into heat, light or mechanical energy.
Core rules
- Every appliance has a supply cord and plug, a control, an energy converter and a safety enclosure. Heating appliances use a resistive element; motor appliances use a motor; refrigeration uses a compressor and refrigerant cycle.
- An electric iron has a nichrome element, soleplate and bimetallic thermostat. A kettle has an immersed element and steam or thermal cut-out. A fan has a capacitor-run motor, blades and regulator. A mixer has a universal motor, speed control and coupling.
- A refrigerator transfers heat from the cabinet to the room using compressor, condenser, capillary and evaporator. The thermostat cycles the compressor.
- Ratings are input power, not output. Motor appliances draw starting current above running current.
Worked example
A 750 W mixer grinder runs slowly and smells hot under load. The supply and plug are sound, but the blades are stiff. The motor draws high current because the load is excessive. The fault is mechanical: jammed bearing or food packing, not necessarily the fuse. Clear the load, check the bearing and inspect the motor winding only after isolation.
Traps
Do not treat a motor appliance as a pure resistor. Do not assume a higher wattage always means more useful output. Do not bypass a thermal cut-out to make a kettle work. Do not test a refrigerator compressor by shorting the relay.