Maharashtra HSC Multi-Skill Electrical (NSQF) key terms

A thin metal wire or strip placed in a circuit that melts and opens the circuit when current exceeds its rating, protecting wiring and equipment from overheating and fire.

A resettable switching device that automatically trips on overload or short circuit, using thermal and magnetic elements, and can be manually reclosed after the fault is cleared.

A protective device that compares live and neutral currents and trips when the difference, caused by leakage to earth, exceeds a set value such as 30 mA.

Deliberately connecting exposed metal parts and the neutral point of a supply to the general mass of earth through a low-resistance path, so fault current flows safely and touch voltage stays low.

A copper or galvanized rod, plate, or pipe buried in the soil to make reliable contact with earth; its resistance depends on soil resistivity, moisture, and depth.

A measurement, usually by the fall-of-potential or three-pole method, of the resistance between an earth electrode and surrounding soil, checked against the permitted value.

The relationship stating that in a linear conductor at constant temperature, voltage equals current multiplied by resistance, so any one quantity can be calculated from the other two.

The ratio of true power in watts to apparent power in volt-amperes, equal to the cosine of the phase angle between voltage and current in an AC circuit.

A connection in which components form a single path, so the same current flows through each and the total resistance is the sum of individual resistances.

A connection in which components are across the same two points, so voltage is common to all and the total current is the sum of branch currents.

An unintended low-resistance path between conductors or between a live conductor and earth, causing very high current that must be cleared quickly by a protective device.

A condition in which a circuit or motor carries more current than its rating for a period, producing excess heat without the extremely high current of a short circuit.

A test instrument combining voltmeter, ammeter, and ohmmeter functions, used to measure AC and DC voltage, current, resistance, and often continuity and diode drop.

An instrument that applies a high DC test voltage, commonly 500 V or 1000 V, to measure insulation resistance in megohms between windings, conductors, and earth.

A meter with a split jaw that surrounds a conductor and measures current from the magnetic field it produces, allowing measurement without breaking the circuit.

A check, usually made with a multimeter on the resistance or buzzer range, confirming that a conductor or switch contact provides a complete low-resistance path.

A device that integrates power over time and records electrical energy consumed in kilowatt-hours, forming the basis for consumer billing.

An instrument transformer whose primary carries the line current and whose secondary supplies a proportional, isolated, reduced current to meters and relays.

A switch with one common terminal and two way terminals, wired in pairs so that a lamp can be controlled from either of two positions, as on a staircase.

A four-terminal switch inserted between two two-way switches in a circuit so that a lamp can be controlled from three or more positions.

The fixed installation of cables, conduits, switches, sockets, and distribution boards inside a dwelling, designed for safety, adequate capacity, and ease of maintenance.

An installation method in which insulated conductors are drawn through metal or PVC pipes fixed to the surface or buried in walls, giving mechanical and weather protection.

A standard number or cross-sectional area, such as 1.5 sq mm or 2.5 sq mm, indicating conductor size and therefore its current-carrying capacity.

An enclosure containing a main switch, busbars, and outgoing protective devices that divides the supply into separate final circuits within an installation.

A motor starter that connects the stator directly across the supply through contactors and overload protection, suitable for small three-phase induction motors.

A reduced-voltage starter that runs the motor windings in star during starting to cut starting current, then changes to delta for normal running.

An electromagnetically operated switch with heavy-duty main contacts and a coil, used to switch motor circuits repeatedly under remote or automatic control.

A protection device with bimetallic elements heated by motor current that trip a normally closed contact when sustained overload occurs, de-energizing the contactor coil.

An electrically operated switch in which a coil actuates contacts to control another circuit, often used for interlocking, signalling, or switching larger loads.

The low-power wiring of push buttons, auxiliary contacts, coils, and relays that determines when main contactors operate, as distinct from the power circuit.

A control arrangement in which the operation of one contactor or device is made conditional on the state of another, preventing unsafe simultaneous operation.

A motor control scheme using two contactors with swapped supply phases and electrical interlocking to reverse the direction of rotation of a three-phase motor.

An AC motor in which a rotating magnetic field from the stator induces currents in a short-circuited rotor, producing torque without brushes or slip rings.

The difference between synchronous speed and actual rotor speed of an induction motor, usually expressed as a percentage of synchronous speed.

A static device with two or more windings coupled magnetically through a common core, which changes AC voltage and current levels at nearly constant frequency and power.

The resistance offered by insulation between conductors or to earth; a low value indicates moisture, dirt, or degradation and warns of impending failure.

Current that flows from a live conductor to earth through faulty insulation or a person, rather than returning through the intended neutral path.

A systematic process of gathering symptoms, testing sections of a circuit, and eliminating causes to locate the defective component or connection quickly and safely.

A drawing that represents a power system using single lines and standard symbols, showing sources, switches, transformers, and feeders without every conductor.

A drawing showing the actual connections between devices with each conductor represented, used for installation, testing, and tracing circuits during maintenance.

Calculating quantities of cable, conduit, accessories, and labour from drawings and specifications, then applying rates to arrive at the expected project cost.

An itemized schedule listing materials and work with their descriptions, units, and quantities, prepared from drawings to support tendering and cost control.

Wearable safety items such as insulated gloves, safety shoes, helmet, and goggles that reduce the risk of electric shock, burns, and physical injury at work.

A safety procedure in which the supply is isolated, locked, and tagged with a warning so equipment cannot be re-energized while someone is working on it.