Odisha CHSE +2 Vocational EDA (Electrical Domestic Appliances) flashcards

34 cards. Read the term and the definition here. The deck at the top of this page is optional.

Ohm's law

Current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance, expressed as V = I × R for a constant-temperature conductor.

Power factor

Ratio of true power in watts to apparent power in volt-amperes in an AC circuit; equals cosine of the phase angle between voltage and current for sinusoidal supply.

Megger test

Insulation resistance measurement made with a high-voltage DC instrument, usually 500 V, between conductors and earth; a reading below one megohm indicates deteriorating or damaged insulation.

Copper versus aluminium

Copper has lower resistivity, about 1.72 × 10⁻⁸ ohm-metre, than aluminium at about 2.83 × 10⁻⁸ ohm-metre, so aluminium conductors need a larger cross-section for the same current rating.

Nichrome alloy

Nickel-chromium resistance alloy with high resistivity, good oxidation resistance and a melting point near 1400 degrees Celsius, widely used for heating elements in irons, heaters and ovens.

PVC insulation

Polyvinyl chloride compound used as wire insulation and cable sheath, suitable for conductor temperatures up to about 70 degrees Celsius in general domestic wiring applications.

Earth pin position

In a three-pin plug the earth pin is the longest and thickest, placed at the top; it opens the socket shutter and connects earth before live and neutral make contact.

RCCB function

Residual current circuit breaker that detects imbalance between phase and neutral currents caused by earth leakage; a 30 mA rating protects people from electric shock.

Switch in phase conductor

Domestic switches must be connected in the live or phase conductor so that switching off isolates the appliance from supply and the holder or appliance body is not left live.

Loop-in wiring system

Wiring method where the supply cable loops from one ceiling rose to the next, each rose feeding a switch drop, so all joints are accessible at the rose rather than buried in the wall.

Conduit wiring

Wiring in which insulated cables are drawn through metal or PVC pipes fixed on the surface or concealed in walls, allowing rewiring later without disturbing the building structure.

Diversity factor

Ratio of the maximum demand of an installation to its total connected load, used to size the main switch, cable and meter below the arithmetic sum of all loads.

MCB Type C

Miniature circuit breaker that trips magnetically at five to ten times its rated current, suited to motors and inductive loads that draw high starting currents.

Two-way switch circuit

Circuit using two two-way switches joined by a three-wire strapper so that one lamp can be controlled from either of two positions, as on a staircase.

Short-circuit current

Current flowing when phase contacts neutral or earth through a very low impedance; it is limited only by the loop impedance and must be interrupted by the protective device.

Bimetallic thermostat

Temperature control device made of two bonded metals with different expansion coefficients; heating bends the strip and opens the contact at the set temperature.

Heating element resistance

Resistance of a heating element calculated from supply voltage and rated power using R = V squared divided by P; a 1000 W, 230 V element is about 53 ohms.

Geyser sacrificial anode

Magnesium or aluminium rod inside a storage water heater tank that corrodes in preference to the steel tank, protecting the tank from rust and extending its service life.

Fan capacitor failure

When the run capacitor of a ceiling fan loses capacitance or shorts, the motor hums without rotating or runs very slowly and needs a capacitor of the same microfarad and voltage rating.

Universal motor

Series-wound motor with a commutator and carbon brushes that runs on AC or DC and reaches high speed; used in mixers and grinders, with brush wear a common fault.

Washing machine drain fault

Failure to empty the tub is usually caused by a blocked lint filter, kinked drain hose, faulty drain pump or a pressure switch that does not sense the empty level.

Refrigeration cycle

Continuous process in which the compressor raises refrigerant pressure, the condenser rejects latent heat, the expansion device drops pressure, and the evaporator absorbs heat from the cabinet.

Ton of refrigeration

Cooling capacity equal to 3.517 kilowatts, the heat absorbed to melt one ton of ice in twenty-four hours; a one-ton room air conditioner is rated at about 12000 BTU per hour.

R-600a refrigerant

Isobutane used in many modern domestic refrigerators; it has low ozone-depleting and global-warming potential but is flammable, so service work must avoid sparks and open flames.

Fluorescent lamp choke

Inductive ballast connected in series with a fluorescent tube to limit current and provide a voltage surge that starts the discharge after the starter preheats the electrodes.

Luminous efficacy

Measure of lamp performance in lumens of light output per watt of electrical power consumed; LED lamps typically reach 80 to 100 lumens per watt against about 12 for incandescent lamps.

Ceiling fan wobble

Side-to-side movement of a running ceiling fan usually caused by unbalanced or bent blades, loose blade screws or a distorted down rod rather than by an electrical winding fault.

Polarity test

Verification that the phase conductor feeds the switch and the correct socket terminal, that neutral is in its proper terminal, and that earth is connected, using a tester or multimeter.

Earth continuity test

Measurement of resistance from the earth pin of each socket and the metal body of each appliance back to the earth electrode, confirming a low-resistance protective path.

Open circuit fault

Break in the current path giving zero current, with full supply voltage appearing across the break; found by continuity testing along the circuit with the supply isolated.

Udyam registration

Online Indian government registration for micro, small and medium enterprises, giving the business a formal identity and access to schemes, subsidies and easier credit.

Estimate components

A service quotation combines material cost, labour charge, overheads and profit margin, with a contingency allowance and a written scope so the customer knows what is covered.

Workshop record book

Internal assessment document in which each practical job is entered with circuit diagram, tools used, test readings and result, countersigned by the instructor.

Pre-energisation test sheet

Checklist recording continuity, insulation resistance, polarity and earth continuity results before a newly wired board or installation is connected to supply.