Domestic Appliances and Repairs
Overview
Domestic Appliances and Repairs is a key chapter in ITI Electrician Semester 4 (NCVT). It covers working principles, construction, common faults, and repair methods of household electrical appliances such as electric iron, mixer-grinder, ceiling fan, refrigerator, washing machine, and water heater. Understanding wiring, safety precautions, and troubleshooting techniques is essential for both theory and practical examinations.
Typed Notes
Electric Iron – Construction and Faults
An electric iron converts electrical energy into heat energy using a nichrome heating element embedded in mica sheets for insulation. A bimetallic thermostat automatically cuts off current when the set temperature is reached. The sole plate is made of cast iron or aluminium. Common faults include: no heat (open heating element), excessive heat (faulty thermostat), leakage to body (damaged mica insulation), and sparking at plug (loose connections). Always check with a megger before repair. Rated wattage is typically 750W–1000W at 230V AC.
Ceiling Fan – Working and Speed Control
A ceiling fan uses a single-phase capacitor-start capacitor-run induction motor. The capacitor (typically 2.5 µF–4 µF) creates a phase difference to produce starting torque. Speed regulation is done by a resistance-type regulator (older) or electronic TRIAC-based regulator (modern). Common faults: fan not starting (capacitor failure or open winding), humming without rotation (capacitor fault), slow speed (low voltage or worn bearings), and vibration (unbalanced blades or loose screws). Lubrication of bearings with machine oil is essential during maintenance. Rated power: 50W–75W at 230V.
Refrigerator – Vapour Compression Cycle
A refrigerator operates on the vapour compression refrigeration cycle. The compressor compresses refrigerant gas (earlier R-12/Freon, now eco-friendly R-134a or R-600a). The condenser releases heat outside, the expansion valve reduces pressure, and the evaporator absorbs heat from inside the cabinet, causing cooling. The thermostat maintains temperature between 2°C–8°C in the fresh food compartment. Common faults: not cooling (gas leakage or compressor failure), excessive frost (door gasket damage), compressor running continuously (thermostat fault). The hermetically sealed compressor is most commonly used in domestic refrigerators.
Washing Machine and Water Heater
A semi-automatic washing machine uses a single-phase induction motor for the wash tub and a separate pump motor for draining. A timer controls wash and spin cycles. Common faults: motor not running (capacitor or winding fault), water not draining (blocked pump). A storage-type water heater (geyser) has a copper or stainless steel tank, a heating element (1000W–3000W), a thermostat (60°C–75°C), a magnesium anode rod (to prevent corrosion), and a pressure relief valve (safety device). Common fault: no hot water (burnt element or tripped thermostat). Always earth the body of the geyser.
Topics & Sub-topics
Har topic ke saath sub-topics aur example — chapter ka complete coverage.
01Fans and Coolers
- Ceiling fan: capacitor motor, regulator
- Speed via winding taps / electronics
- Common faults: capacitor, bearing
Fan slow chal raha — 90% cases capacitor 2.25 µF kam ho gaya.
02Heating Appliances
- Iron, geyser, toaster — nichrome element
- Thermostat control
- Wattage vs heating time
Electric iron 1000 W — element khula to continuity test se turant pakdo.
03Mixers and Washing Machines
- Universal motor + gear (mixer)
- Washing: timer + motor + pump
- Common faults: carbon brush, coupling
Mixer overload par chal raha — carbon brush 2 mm se kam ho to badlo.
04Repair Safety and Testing
- Unplug before opening
- Multimeter + series lamp test
- Insulation check after repair
Repair ke baad pehle series bulb ke through supply — short ho to bulb full glow.
Key Concepts
Revision ke liye ek nazar — exam se pehle yahi padhna hai.
- 01Electric iron works on the principle of heating effect of electric current; thermostat regulates temperature between 120°C–240°C.
- 02Ceiling fan motor is a single-phase induction motor (capacitor-start capacitor-run type); speed is controlled by a regulator (resistance or electronic type).
- 03Refrigerator works on vapour compression cycle; main components are compressor, condenser, expansion valve, and evaporator.
- 04Mixer-grinder uses a universal motor that works on both AC and DC; speed range is 2000–20000 RPM.
- 05Water heater (geyser) uses a nichrome or Kanthal heating element rated typically at 1000W–3000W with a thermostat set around 60°C–75°C.
Questions & Solutions
Pehle khud try karo — phir solution kholo. Yahi tariqa topper banata hai.
What type of motor is used in a mixer-grinder and why is it preferred?
Name the components of the vapour compression cycle used in a domestic refrigerator.
What is the function of a thermostat in an electric iron?
A ceiling fan hums but does not rotate. What is the most likely fault and how will you rectify it?
What is the purpose of the magnesium anode rod in a storage water heater?
Domestic appliances use heating effect, electromagnetic induction, or vapour compression principles. Electric iron (nichrome element, bimetallic thermostat), ceiling fan (capacitor induction motor), refrigerator (vapour compression, R-134a refrigerant), mixer-grinder (universal motor), and water heater (heating element + thermostat) are the core appliances. Fault diagnosis, safety earthing, and correct component replacement are critical skills tested in ITI Electrician Semester 4 NCVT examinations.
Chapter-end quiz
4 MCQsOption tap karo — turant pata chalega sahi ya galat, explanation ke saath.
Q1.Which refrigerant is currently used in eco-friendly domestic refrigerators as a replacement for R-12?
Q2.The heating element of an electric iron is made of which material?
Q3.What is the typical capacitor rating used in a standard ceiling fan?
Q4.Which safety device is mandatory on a storage-type water heater (geyser) to prevent explosion due to excess pressure?
Mark karo — dashboard par progress dikhega.