UPMSP Vocational Domestic Electrical Appliances & Repair cheat sheet

Ohm's law: V = I × R; power P = V × I = I²R = V²/R. Single-phase domestic supply in India is 230 V, 50 Hz; three-phase is 415 V between phases.

A 1.5 mm² copper conductor carries about 10–16 A, 2.5 mm² about 16–22 A, and 4 mm² about 25–32 A in domestic wiring; choose cable rating above the appliance full-load current.

Earth wire resistance to earth should be low enough that fault current trips the MCB instantly; IS 732 requires earth continuity and separate earth conductor (green or green-yellow).

Use ELCB/RCCB of 30 mA sensitivity for shock protection in wet areas (bathroom, kitchen, geyser); MCB protects cable against overload and short circuit, not against shock.

Current through the body above about 30 mA can cause muscle contraction and cannot-let-go; 50–100 mA across the heart is potentially fatal. Never work on live circuits.

First aid for electric shock: switch off supply, use dry insulating material to separate victim, call help, start CPR if breathing stopped, treat burns with clean dry cloth.

Class B fire (electrical) needs CO2 or dry powder extinguisher; never water. Switch off mains before fighting any electrical fire.

Series circuit: same current, voltages add, R_total = R1 + R2. Parallel circuit: same voltage, currents add, 1/R_total = 1/R1 + 1/R2.

Multimeter in voltage mode is connected in parallel across the point; in current mode it is connected in series and the circuit must be broken. Resistance is measured with the component de-energized.

Continuity test (buzzer mode) confirms a closed path; a good fuse or switch shows near-zero ohms, an open circuit shows overload (OL).

Clamp meter reads AC current by surrounding one conductor only; clamping both live and neutral together reads near zero because fields cancel.

Insulation resistance is measured with a megger at 500 V DC; a healthy domestic appliance motor winding reads above 1 MΩ to earth, below that indicates moisture or insulation failure.

Soldering iron for electronics is 25–40 W with rosin-core solder; use flux sparingly, keep tip tinned, and never use acid flux on copper wiring joints.

Insulated screwdrivers, pliers, wire stripper, crimping tool, and test lamp are standard; verify a tester on a known live point before trusting a dead reading.

Micrometer or vernier caliper measures wire gauge and shaft diameter; feeler gauge checks bearing clearance; torque screwdriver prevents over-tightening terminal screws.

A series test lamp limits current and is used for tracing; a neon screwdriver indicates live presence only and must not be relied on to prove dead.

Domestic circuits use PVC-insulated copper cable: 1.0/1.5 mm² for lighting, 2.5 mm² for 6 A sockets, 4 mm² for 16 A power points, and 6 mm² for sub-mains to geyser or AC.

Live is red or brown, neutral is black or blue, earth is green or green-yellow. New IEC code uses brown (L), blue (N), green-yellow (E).

Loop-in ceiling rose system: supply loops from rose to rose; switch drops to the switch and the lamp connects at the rose. Two-way switching uses two strappers between two SPDT switches.

Socket wiring: live to right-hand terminal viewed from front, neutral to left, earth to top; switch should break the live conductor, never the neutral.

MCB rating must be below cable current rating and above appliance current; a 16 A MCB protects a 2.5 mm² circuit but not a 1.0 mm² lighting circuit.

Conduit wiring: PVC conduit for surface and concealed work, bends radius at least 6× conduit diameter, no more than two 90° bends between draw boxes.

Earthing types: plate earth, pipe earth, and strip earth; earth pit should be kept moist with charcoal and salt. Earth resistance should be under 5 Ω for domestic installation.

Kitchen and bathroom sockets need IP44 or higher and must be fed from a 30 mA RCCB; geyser needs a double-pole isolator within reach.

Heating element resistance: P = V²/R, so a 1000 W, 230 V element has R ≈ 53 Ω. An open element reads infinite ohms and must be replaced.

Electric iron: thermostat (bimetallic strip) controls soleplate temperature; no heat with pilot lamp on indicates open element or faulty thermostat contacts.

Geyser: thermostat and thermal cut-out are in series with the element. A tripping MCB on a geyser commonly indicates a leaking element or moisture in the terminal block.

Oven: heating elements in top and bottom, thermostat, timer, and door interlock switch. Uneven baking points to a faulty top or bottom element or a stuck thermostat.

Induction cooktop works by eddy currents in the ferromagnetic base of the pan; it does not heat glass, aluminium, or copper cookware. No heat with a suitable pan points to IGBT or coil fault.

Heater fan coil: open coil means no heat but fan runs; a shorted coil trips the MCB. Check element resistance before replacing the whole assembly.

Thermal fuse in heaters and irons is a one-shot device; if it is open, always find the cause (stuck thermostat, blocked airflow) before fitting a new one.

Water scale on geyser elements causes overheating and early failure; descale with dilute citric acid solution, never with abrasive on the element sheath.

Universal motor in mixer-grinder has brushes and a commutator; worn brushes cause sparking, weak torque, and intermittent running. Check brush length and commutator wear.

Mixer motor has a thermal overload protector in the winding; if it trips repeatedly, check for overload, jammed coupler, or shorted winding.

Ceiling fan: capacitor-run single-phase motor. Fan not starting but humming usually means a failed capacitor (typically 2.25–3.5 µF); replace with same rating.

Fan speed regulator is a triac-based dimmer; a burnt regulator gives no speed control. Fan winding resistance can be compared across coils to find an open winding.

Washing machine: inlet valve, water level switch (pressure switch), timer or PCB, motor capacitor, and drain pump. No drain usually means a blocked filter or failed pump.

Semi-automatic washing machine uses a capacitor-run motor with a reversing switch for wash and spin; a motor that runs in one direction only points to a faulty reversing contact.

Water pump: monoblock or submersible. Low discharge can come from air lock, worn impeller, suction leak, or wrong rotation direction on three-phase pumps.

Submersible pump insulation must be checked with a megger before installation; a reading below 1 MΩ indicates a wet winding and the pump must be dried or rewound.

Refrigeration cycle: compressor raises pressure and temperature, condenser rejects heat, expansion device drops pressure, evaporator absorbs heat. Cooling happens in the evaporator.

Refrigerants: R-134a for domestic refrigerators, R-600a (isobutane) for many modern fridges, R-32 and R-410A for split ACs. R-600a is flammable; no open flame during service.

Superheat is evaporator outlet temperature minus saturation temperature; subcooling is saturation temperature minus condenser outlet temperature. Normal superheat is 5–8 K.

Fridge not cooling: check door seal, condenser cleanliness, thermostat setting, then compressor running, then gas charge. Frost pattern on evaporator shows charge distribution.

Compressor does not start: check supply, overload protector, start relay (PTC or capacitor), and winding resistance. A good compressor winding has low resistance between terminals and high resistance to body.

Split AC: indoor unit has evaporator and blower, outdoor unit has compressor and condenser. Water leaking indoors usually means a blocked drain pipe or dirty filter.

Air conditioning capacity is measured in tons or BTU; 1 ton ≈ 3.5 kW. Room size, insulation, and sun exposure determine the right capacity.

Leak testing uses soap solution, nitrogen pressure test, or electronic leak detector. Never use oxygen for pressure testing; it forms an explosive mixture with oil.

Triac controls AC power by phase angle; used in fan regulators, dimmers, and heater controls. A shorted triac gives full power all the time; an open triac gives no output.

Diode bridge rectifier converts AC to DC in SMPS supplies; a shorted diode blows the fuse, an open diode gives low or no DC output.

SMPS in inverter AC and LED driver works by switching at high frequency; check fuse, bridge, switching MOSFET, and output capacitor in that order.

Sensors: thermistor (NTC) for temperature, IR sensor for remote and motion, Hall sensor for motor speed, and pressure switch for water level. A faulty NTC reads open or wrong resistance at room temperature.

Inverter AC and inverter fridge use a variable-frequency drive; the IPM module drives the compressor. An IPM fault code usually means a shorted compressor or failed module.

LED lamp: driver converts 230 V AC to low DC. Flickering usually means a failing capacitor in the driver; a dead lamp with good LEDs points to the driver.

Inverter and stabilizer: check input and output voltage with a multimeter; a relay chatter often means a faulty comparator or low battery in the control circuit.

Microcontroller boards are replaced rather than repaired at the component level in most service shops; confirm supply, sensor inputs, and relay outputs before condemning the board.

Diagnosis sequence: gather complaint, check supply and plug, check fuse or MCB, then isolate the appliance and test with a multimeter before opening covers.

Divide the circuit: test continuity of switch, thermostat, fuse, and element separately. The first open or short found is usually the fault.

Visual inspection first: burnt smell, blackened terminals, loose screws, rodent damage, water entry, and swollen capacitors reveal many faults before any meter is used.

Test a heating element by resistance; test a motor by winding resistance and insulation to body; test a capacitor by capacitance mode or by charging and observing a spark with a safe resistor.

After repair, do a safety test: insulation resistance above 1 MΩ, earth continuity below 0.1 Ω, and no exposed live parts. Run the appliance for a few minutes under load.

Document the complaint, tests done, parts replaced, and charges on the job sheet; this protects both customer and technician in a dispute.

Never bypass a thermal fuse, earth wire, or door interlock to make an appliance work; this creates a fire or shock hazard and voids the warranty.

Use the correct replacement rating: same voltage, same or higher current, same capacitance for capacitors, and same temperature rating for thermal fuses.

Service pricing: charge for diagnosis, parts at cost plus a margin, and labour by job type. A written estimate before work prevents disputes.

Keep a stock register and spare parts inventory; fast-moving items are fuses, capacitors, thermostats, elements, brushes, and fan regulators.

Warranty terms: manufacturer warranty covers defects, not misuse; a service shop's own repair warranty is typically 1–3 months on labour and part.

GST registration is required above the turnover threshold; a small service shop can operate as a proprietorship with a current account and proper invoicing.

Customer complaint handling: listen fully, repeat the problem back, give a time estimate, and follow up after delivery. Never argue in front of other customers.

Record keeping: job number, customer details, appliance model and serial number, fault, parts used, and payment mode. This helps warranty claims and repeat business.

Marketing for a repair shop: local signage, referrals, Google Business listing, and service reminders for geyser and AC servicing before season.

Safety of staff and customer property: use a mat, remove jewellery, keep tools insulated, and confirm the mains is off before opening any appliance in the customer's home.

PPE for electrical work: insulated gloves, safety shoes, goggles, and helmet where needed. Rubber mat under feet when working near live parts.

Lock-out/tag-out: switch off, lock the isolator, tag it, and verify dead with a tester before touching conductors.

Personal grooming and uniform build customer trust; carry an ID card and a clean tool bag to every service call.

Communication skills: greet the customer, explain the fault in simple language, avoid technical jargon, and confirm the final bill before leaving.

Time management: plan the day's calls by location, keep a buffer for emergencies, and call the customer if delayed.

Workplace hazards: sharp edges, hot surfaces, refrigerant burns, electric shock, and slips. Report injuries and keep a first-aid box in the shop.

Attendance, punctuality, and honesty in billing are core employability skills; a technician who overstates faults loses repeat customers.

Continuous learning: read service manuals, attend manufacturer training, and follow BIS safety standards for domestic appliances.

Energy cost: units (kWh) = watts × hours ÷ 1000. A 2000 W geyser run for 1 hour consumes 2 units.

Voltage drop in a cable should be kept under 3% of supply voltage for domestic circuits to avoid appliance malfunction.

Fuse rating: choose a fuse about 1.5–2 times the normal running current to allow starting surge of motors.

Insulation colour code: brown live, blue neutral, green-yellow earth. Old code: red live, black neutral, green earth.

Resistance of a copper conductor increases with temperature; a hot motor winding reads higher resistance than a cold one.

Leakage current above 30 mA is dangerous; RCCB trips at 30 mA within 30 ms, protecting people rather than equipment.

A short circuit gives near-zero resistance and very high current; an overload gives moderately high current over a longer time.

Before using a multimeter, select the correct function and range; measuring voltage on the resistance range can damage the meter.

Continuity of a wire: disconnect both ends, set to ohms, expect below 1 Ω for a short run of copper wire.

Capacitance mode on a multimeter checks fan and motor capacitors; a reading far below the marked value means replacement.

Megger test: connect one lead to winding terminal and the other to the metal body; a reading above 1 MΩ is acceptable for domestic motors.

Clamp meter should be zeroed before use and should enclose only one conductor; a reading of zero with load running means the wrong conductor or a faulty clamp.

Torque and tightness: loose terminal screws cause heating and burning; check tightness after every repair.

Tool care: wipe tools after use, keep insulated handles free of cuts, and replace damaged insulation immediately.

A 6 A lighting circuit is wired with 1.0–1.5 mm² cable and protected by a 6 A MCB; a 16 A power circuit uses 2.5–4 mm² cable.

Total connected load per circuit should not exceed the MCB rating; split heavy loads like geyser, AC, and oven onto separate circuits.

Switch must be in the live conductor; a switch in the neutral leaves the appliance live even when off.

Two-way switch wiring: common of first switch to live, common of second switch to lamp, and two strappers between the L1 and L2 terminals.

Earthing must be continuous to every socket and metal appliance body; never use the neutral as earth.

Concealed wiring needs conduit buried at least 150 mm below plaster and a draw box at every bend or junction.

Socket outlets in a kitchen should be at least 1.2 m above floor and away from the sink; bathroom sockets need RCCB protection and IP44 rating.

Iron not heating, pilot lamp on: open element or open thermostat. Iron overheating: thermostat contacts stuck closed or a wrong-rated thermostat fitted.

Geyser trips MCB: test element insulation to body with a megger; a reading below 1 MΩ means the element is leaking and must be replaced.

Heater with fan: no heat but fan runs means open element; heat with no fan means open fan winding or blocked airflow, which can trip the thermal cut-out.

Oven temperature inaccurate: check thermostat probe and calibration; a 20 °C error is acceptable, larger errors need thermostat replacement.

Induction cooktop not detecting a pan: check pan base is ferromagnetic, check the pan sensor, then the coil and IGBT. Error codes usually point to the sensor.

Thermal fuse replacement must match the temperature rating marked on the old fuse; a higher rating defeats protection.

Descale geyser and heater elements regularly; scale insulates the element and causes overheating and premature failure.

Mixer-grinder sparking at brushes: worn brushes or a rough commutator. Replace brushes and clean the commutator with fine emery cloth.

Mixer runs slow under load: check capacitor if fitted, check for a shorted turn in the field winding, and check the coupler for slipping.

Ceiling fan hums but does not turn: failed capacitor is the most common cause; replace with the same microfarad rating and voltage.

Washing machine does not fill: check inlet valve, water supply, and pressure switch. Does not drain: check drain filter, hose, and pump.

Washing machine motor runs in one direction only: faulty reversing switch or timer contact; check the timer cam and wiring.

Water pump loses prime: air leak in suction pipe, worn foot valve, or low water level. Check suction joints before opening the pump.

Submersible pump trips MCB: insulation failure from water entry or a shorted winding; megger test before re-installation.

Fridge warm with compressor running: check condenser airflow, door gasket, and refrigerant charge; a partly frosted evaporator indicates low charge.

Compressor hot and tripping overload: check supply voltage, start relay, and capacitor; a seized compressor draws locked-rotor current and trips quickly.

Split AC not cooling: check filter, indoor coil, outdoor condenser, and gas pressure. Low suction pressure with normal superheat suggests undercharge.

Water leaking from indoor unit: blocked drain pipe, dirty filter, or incorrect slope of the drain; clean and re-route.

Refrigerant charging must be done by weight or by superheat/subcooling method; never guess by feel of the pipes.

R-600a is flammable: ventilate the area, avoid sparks, and use a spark-free vacuum pump when servicing.

AC installation: indoor unit at least 2.3 m above floor, outdoor unit with clearance for airflow, and drain pipe sloping downward.

SMPS output absent: check fuse, bridge rectifier, and switching MOSFET. A shorted MOSFET usually means the PWM controller is also damaged.

Triac regulator with full output: triac shorted. With no output: triac open or diac faulty. Test diac with a resistance check.

NTC thermistor reads open or very high: replace with the same resistance at 25 °C and same beta value.

Inverter AC error code for IPM: check compressor winding resistance and insulation, then the IPM module and its heat sink compound.

LED driver output low: check electrolytic capacitor ESR and the output diode; a swollen capacitor is a common cause of flicker.

Remote not working: check battery, IR LED with a phone camera, and the receiver sensor on the appliance board.

Relay clicking repeatedly in a stabilizer: check input voltage sense circuit and the comparator; low voltage cut-off may be set too high.

Always verify the complaint yourself; the customer's description may point to a different fault than the one present.

Test components in circuit where possible; desolder only when the reading is ambiguous.

Replace a part only after confirming it is faulty; guessing wastes parts and time and can introduce new faults.

After replacing a fuse, find why it blew; a fuse that blows again immediately means a short circuit downstream.

Safety test after every repair: insulation resistance, earth continuity, and a short run under load before returning the appliance.

Keep a job sheet with model, serial number, fault found, parts replaced, and test results; this supports warranty and repeat service.

Never return an appliance with the earth disconnected or a bypassed safety device; it is a legal and safety violation.

Set labour charges by job type and publish a rate card; charge diagnosis separately from repair to avoid disputes.

Keep a minimum stock of fast-moving spares and reorder when stock falls below one week's usage.

Invoice must show shop name, GSTIN if registered, job number, parts, labour, and total; keep a copy for records.

Offer a written repair warranty of 1–3 months on labour and parts, and state exclusions clearly.

Handle complaints by listening, apologizing where appropriate, fixing the issue, and following up; a resolved complaint often creates a loyal customer.

Track repeat customers and send seasonal service reminders for AC, geyser, and fan before summer and winter.

Maintain a safe shop: insulated tools, a fire extinguisher, a first-aid box, and a clearly marked main switch.

Lock-out/tag-out before any repair: switch off, lock, tag, and verify dead with a tester.

Use insulated gloves, safety shoes, and goggles; stand on a rubber mat when working near live parts.

Never work alone on a live circuit; keep a second person nearby who can switch off the supply.

Explain the fault and the repair in simple language, confirm the bill, and give the customer a written job sheet.

Be punctual, keep a clean uniform, carry an ID card, and respect the customer's home and property.

Report injuries and near-misses; keep a first-aid box and fire extinguisher in the shop and service van.

Follow BIS standards and manufacturer service manuals; attend training to keep skills current.

A 30 mA RCCB is the standard personal protection device for domestic wet areas; test it monthly with the test button.

Earth resistance should be under 5 Ω for domestic installations; a higher value means the earth pit needs watering or recharging.

Insulation resistance of a healthy appliance should be above 1 MΩ at 500 V DC; below 0.5 MΩ is unsafe.

Fuse and MCB must be rated above the appliance current and below the cable current rating.

Voltage drop should be under 3% for domestic circuits; long runs need a larger cable.

Never use water on an electrical fire; use CO2 or dry powder and switch off the supply first.

Use a 500 V megger for domestic appliance insulation tests; a 1000 V megger is for higher-voltage equipment.

Use a clamp meter for AC current without breaking the circuit; use a multimeter in series for DC current.

Choose a soldering iron of 25–40 W for electronic boards and 60–100 W for heavier terminals.

Use a wire stripper matched to the wire gauge; cutting insulation with pliers nicks the conductor and weakens it.

Use insulated tools rated for 1000 V when working near live parts.

Calibrate or cross-check a multimeter against a known source before trusting critical readings.

New IEC colour code: brown live, blue neutral, green-yellow earth. Old code: red live, black neutral, green earth.

A switch must break the live conductor; never switch the neutral.

A 16 A socket needs a 2.5–4 mm² cable and a 16 A MCB; a 6 A socket needs 1.5 mm² cable and a 6 A MCB.

Every circuit must have a separate earth conductor run back to the earth pit; never rely on conduit as earth.

Kitchen and bathroom circuits must be protected by a 30 mA RCCB.

Two-way switching uses two strapper wires between the two switches; the lamp connects to the common of the second switch.

Element resistance R = V²/P; a 1500 W, 230 V element reads about 35 Ω.

Open element reads infinite ohms; shorted element reads near zero and trips the MCB.

Thermostat contacts should read near zero ohms when closed and infinite when open; test at room and at operating temperature.

Thermal cut-out is one-shot; if open, find the cause before replacing.

Geyser element insulation below 1 MΩ to body means replacement.

Induction cooktop needs a ferromagnetic pan; aluminium and glass pans will not heat.

Universal motor brushes should be at least 5 mm long; shorter brushes spark and damage the commutator.

Fan capacitor failure is the most common cause of a fan that hums but does not turn.

Motor winding resistance should be balanced across phases or coils; a large difference indicates a shorted turn.

Insulation resistance of a motor winding to body should be above 1 MΩ.

Washing machine drain pump should show low resistance and run when fed 230 V directly; no run means replacement.

Submersible pump must be megger-tested before installation; a wet winding reads low and must be dried.

Normal superheat at the evaporator outlet is 5–8 K; higher superheat suggests undercharge.

Normal subcooling at the condenser outlet is 4–8 K; higher subcooling suggests overcharge or a restriction.

Low suction pressure with low superheat suggests a restriction; low suction with high superheat suggests undercharge.

Condenser must be clean and have airflow; a dirty condenser raises head pressure and reduces cooling.

R-600a is flammable; ventilate and avoid sparks during service.

1 ton of cooling ≈ 3.5 kW; match AC capacity to room heat load.

Diode test: forward drop about 0.6 V for silicon, open in reverse; a shorted diode reads zero both ways.

Capacitor test: a swollen top or low capacitance reading means replacement; ESR meter gives a better check.

Triac test: gate to MT1 should show a junction drop; a shorted triac reads zero between MT1 and MT2.

NTC thermistor resistance falls as temperature rises; an open thermistor gives a false high-temperature error.

SMPS fuse blown: check bridge rectifier and switching MOSFET before replacing the fuse.

IR receiver output should toggle when a remote is pressed; use a phone camera to check the remote's IR LED.

Insulation resistance above 1 MΩ at 500 V DC is the pass mark for a domestic appliance.

Earth continuity should be below 0.1 Ω from plug earth pin to appliance body.

No exposed live parts after reassembly; check covers and screws.

Run the appliance under load for a few minutes and check for abnormal heat, noise, or smell.

Record test results on the job sheet before returning the appliance.

Never bypass a thermal fuse, earth, or door interlock; it is unsafe and voids warranty.

Charge diagnosis separately from repair; publish a rate card to avoid disputes.

Keep a stock register and reorder fast-moving spares before stock runs out.

Invoice must show shop name, GSTIN if registered, job number, parts, labour, and total.

Offer a written 1–3 month warranty on labour and parts with clear exclusions.

Record customer details, appliance model, serial number, fault, and parts used for each job.

Send seasonal service reminders for AC, geyser, and fan to build repeat business.

Lock-out/tag-out before repair: switch off, lock, tag, verify dead.

Wear insulated gloves, safety shoes, and goggles; stand on a rubber mat near live parts.

Never work alone on a live circuit; keep a second person who can switch off supply.

Explain the fault and repair in simple language and confirm the bill before leaving.

Be punctual, keep a clean uniform, and carry an ID card.

Report injuries and keep a first-aid box and fire extinguisher in the shop and van.