Maharashtra SSC Electrical Technology Pre-Voc/NSQF key terms

The electrical pressure between two points that pushes charge through a circuit, measured in volts with a voltmeter connected in parallel across those points.

The rate at which electric charge flows past a point in a conductor, measured in amperes; an ammeter is connected in series to measure it.

The relationship stating that current through a conductor equals the voltage across it divided by its resistance, written V = IR, valid at constant temperature.

The opposition a material offers to the flow of current, measured in ohms; it depends on material, length, cross-sectional area and temperature.

A conductor such as copper allows charge to flow easily, while an insulator such as rubber or PVC blocks it; this difference decides which material carries current and which protects people.

Power is the rate of using electrical energy, measured in watts; energy is power multiplied by time, and electricity bills charge for energy in kilowatt-hours.

In a series circuit one path carries the same current through every component; in a parallel circuit each branch gets full supply voltage, as domestic lamps and sockets are wired.

AC regularly reverses direction and is supplied to homes at about 50 Hz in India; DC flows one way only, as from cells and batteries or rectified adaptors.

The number of complete AC cycles per second, measured in hertz; Indian public supply runs at 50 Hz, which sets the speed of induction motors.

Deliberately connecting exposed metal parts and the supply neutral point to the general mass of earth so fault current trips protection and touch voltage stays safe.

A deliberately weak link of wire or strip that melts and opens the circuit when current exceeds its rating, protecting wiring from overheating and fire.

A resettable switch that trips automatically on overload or short circuit, replacing rewirable fuses in distribution boards and marked with its current rating and breaking capacity.

A device that detects small currents leaking to earth, such as through a person or wet appliance, and disconnects the supply within milliseconds to prevent fatal shock.

A standard number describing conductor diameter or cross-sectional area, which fixes how much current a wire can safely carry without overheating.

The maximum current a cable or conductor can carry continuously without its insulation exceeding safe temperature, reduced when cables are bundled or run in hot places.

Polyvinyl chloride sheathing around conductors that provides electrical insulation, mechanical protection and flame resistance; it softens at high temperature, so joints must be sound.

Joining metals by melting a tin-lead or lead-free alloy between them; flux cleans oxide from the surfaces so the solder wets and bonds properly.

A combined instrument that measures voltage, current and resistance, and often continuity and diode drop; the selector and probe sockets must match the quantity being measured.

An instrument applying a high test voltage, commonly 500 V DC, to measure insulation resistance in megohms and reveal damp, aged or damaged insulation.

A check confirming an unbroken low-resistance path, usually with a buzzer or ohmmeter on a dead circuit, used to trace wires and verify joints and earthing.

A meter whose jaws encircle a single conductor and read current from its magnetic field, allowing load measurement without breaking the circuit or touching live metal.

A switch with one common terminal and two way terminals, used in pairs so a lamp can be controlled from two positions such as at each end of a staircase.

A four-terminal switch inserted between two two-way switches so the same lamp can be controlled from three or more positions along a corridor.

The enclosure holding the main switch, protective devices and outgoing circuits, dividing the supply into sub-circuits and providing a single point to isolate the installation.

Adding the wattage of lamps, fans, sockets and fixed appliances to find total connected load and diversified demand, which determines main switch, cable and meter ratings.

The plate and box mounting switches, sockets and regulators at a convenient height, with live parts enclosed and the metal box bonded to earth.

A lamp is the light-producing element such as an LED or fluorescent tube; a luminaire is the complete fitting that holds it, controls its light and connects it to supply.

Appliances converting electricity to heat through a resistance element; faults commonly lie in the element, thermostat, cord or plug, checked by continuity and insulation tests.

A machine converting electrical energy into rotation by magnetic interaction; single-phase types include capacitor-start and split-phase, while three-phase induction motors drive most industry.

A static device with two windings on a common magnetic core that changes AC voltage level; the ratio of turns sets the ratio of secondary to primary voltage.

The number of secondary winding turns divided by primary turns; it equals secondary voltage divided by primary voltage in an ideal transformer and indicates step-up or step-down action.

The speed of the rotating magnetic field in an AC machine, equal to 120 times frequency divided by number of poles, for example 1500 rpm at 50 Hz with four poles.

The small difference between synchronous speed and actual rotor speed of an induction motor, expressed as a fraction or percentage of synchronous speed; it rises with load.

A rechargeable cell using lead plates and dilute sulphuric acid, giving about 2 V per cell; it needs distilled water topping and must never be shorted or overcharged.

The density of battery electrolyte compared with water, measured by a hydrometer; it falls as the cell discharges and indicates state of charge.

A circuit, often using diodes, that converts alternating current into direct current to charge batteries or run DC equipment from mains supply.

A standard simplified graphic standing for a component on a circuit diagram, such as a circle with a cross for a lamp, so any trained reader interprets the drawing alike.

A schematic shows electrical connections logically without regard to physical position, while a wiring diagram shows components in their actual layout with terminal numbers for installation.

A drawing using one line to represent a multi-wire circuit, showing supply, switchgear, protection and loads in sequence; used to plan and document distribution.

Wearable protection such as insulating gloves, safety shoes, helmet and goggles, selected for the hazard; it supplements safe isolation and never replaces it.

The procedure of switching off, proving dead, locking the isolator and attaching a warning tag so a circuit cannot be re-energised while someone works on it.

Switch off or safely separate the casualty from the supply, call emergency help, and begin CPR if breathing has stopped; never touch a person still in contact with live parts.