Maharashtra SSC Electrical Technology Pre-Voc/NSQF flashcards

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

Ohm's law

For a metallic conductor at constant temperature, voltage equals current multiplied by resistance, written V = I × R, with V in volts, I in amperes and R in ohms.

RMS value

The effective value of an alternating quantity that produces the same heating as an equal direct current; for a sine wave it equals peak value divided by the square root of two, about 0.707 times peak.

RCCB 30 mA

A residual current device that trips when the difference between phase and neutral current reaches thirty milliamperes, protecting people from earth leakage and electric shock within milliseconds.

Class C fire

A fire involving flammable gases such as LPG or methane; it is extinguished by cutting off the gas supply and using dry powder or carbon dioxide, never water.

Insulation temperature classes

Standard classification of insulating materials by maximum safe temperature: class A 105 degrees Celsius, class B 130, class F 155 and class H 180, used to select winding insulation.

Silicon steel core

An alloy of iron with about three to four percent silicon, used for transformer and motor laminations because it raises resistivity and narrows the hysteresis loop, cutting eddy and hysteresis losses.

Dielectric strength

The maximum voltage gradient an insulating material can withstand per unit thickness without electrical breakdown, usually expressed in kilovolts per millimetre and reduced by moisture.

ACSR conductor

Aluminium conductor steel reinforced, an overhead line conductor with aluminium strands around a steel core, combining light weight with high mechanical strength for long transmission spans.

Megger insulation test

A test that applies high direct voltage to measure insulation resistance in megohms; a healthy domestic installation reads at least one megohm between conductors and earth.

Clamp meter

An instrument that measures alternating current by sensing the magnetic field around a single conductor, requiring no circuit breakage and reading only one conductor at a time.

Ammeter shunt resistance

A low resistance connected in parallel with a meter movement to extend its current range, calculated as meter resistance divided by the multiplying factor minus one.

Continuity test

A check made with a multimeter or buzzer on a dead circuit to confirm a low-resistance path; a buzzer sounds when the conductor or contact is intact.

Loop-in wiring system

A wiring method in which circuit conductors loop from ceiling rose to ceiling rose and switch drops branch from the rose, keeping all joints accessible for inspection and repair.

Conduit fill rule

The total cross-sectional area of all conductors drawn into a conduit should not exceed about forty percent of the conduit internal area, so that cables can be pulled without damage.

Two-way switch

A three-terminal switch with common, L1 and L2 contacts, used in pairs so that one lamp can be controlled independently from two different positions, as on a staircase.

Intermediate switch

A four-terminal switch inserted between two two-way switches so that a lamp can be controlled from three or more positions, reversing the connection of the travelling wires.

Earth resistance value

The resistance measured between an earth electrode and surrounding soil; it should be below about one ohm at a substation and below five to eight ohms for domestic installations.

Type B MCB

A miniature circuit breaker that trips magnetically at three to five times its rated current, suitable for resistive loads such as lighting and socket circuits in domestic wiring.

Ceiling rose

A ceiling-mounted accessory with terminals for phase, neutral and earth that supports a pendant flexible cord and provides the junction where the lighting circuit is connected.

Distribution board earthing

The arrangement in which separate earth and neutral bars are provided, connected to the earth electrode and supply neutral respectively, with the two never bonded downstream of the supply point.

Bimetallic thermostat

A temperature-sensing switch made of two metals with different expansion rates bonded together; it bends with heat to open or close contacts, controlling irons, geysers and ovens.

Fan capacitor failure

A common fault in capacitor-run ceiling fans where the motor hums but does not rotate; the capacitor loses capacitance or shorts, so it must be replaced with an identical rating.

Microwave capacitor hazard

The high-voltage capacitor in a microwave oven retains a lethal charge after the appliance is unplugged, so it must be discharged through a resistor before any servicing work.

Geyser element test

Measuring resistance across an immersion heater element; infinite resistance means the element is open, while a low reading to the metal body indicates dangerous leakage to earth.

Transformer EMF equation

The relation E equals 4.44 times frequency times turns times maximum flux, giving the induced voltage in a winding and showing that voltage per turn is fixed by flux and frequency.

Induction motor slip

The difference between synchronous speed and actual rotor speed, expressed as a fraction of synchronous speed; it is typically two to five percent at full load.

Star-delta starter

A motor starter that connects the stator in star during starting, reducing phase voltage and starting current to one third, then switches to delta for normal running.

DC motor back EMF

The voltage generated by the rotating armature that opposes the supply voltage; it equals supply voltage minus armature current times armature resistance and limits motor current.

Lead-acid cell voltage

A fully charged lead-acid cell has a nominal electromotive force of about two volts; six such cells connected in series make a twelve-volt battery used in vehicles and inverters.

Ampere-hour capacity

The quantity of charge a battery can deliver, equal to discharge current multiplied by discharge time at a stated rate; a hundred ampere-hour battery delivers five amperes for twenty hours.

Single-line diagram

A drawing that represents a three-phase power circuit with one line and shows the main components and their connections, used for planning and fault tracing in installations.

Ladder control diagram

A schematic in which control contacts and loads are drawn between two vertical supply rails, read left to right, so that relay and contactor logic can be traced easily.

Lockout-tagout

A safety procedure in which each worker places a personal lock and tag on an isolation point, ensuring the supply cannot be restored until that worker removes them.

Break-even quantity

The number of units or jobs at which total revenue equals total cost, calculated as fixed cost divided by selling price minus variable cost per unit.

E-waste disposal

Discarding electronic equipment such as old meters, chargers and circuit boards only through authorised recyclers, because they contain lead, mercury and other hazardous substances.