Assam HS Skill Electrical Mechanics and Electrician key terms

The relationship stating that current through a conductor equals the voltage across it divided by its resistance, written I = V/R for DC circuits at constant temperature.

The work done per unit charge in moving charge between two points in a circuit, measured in volts and often simply called voltage.

Electromotive force: the energy per unit charge supplied by a source such as a cell or generator, measured in volts and distinct from terminal voltage under load.

The opposition a material offers to current flow, measured in ohms, depending on resistivity, length and cross-sectional area of the conductor.

A material property giving the resistance of a unit length and unit cross-section, measured in ohm-metres, used to compare conductors such as copper and aluminium.

The cosine of the phase angle between voltage and current in an AC circuit, equal to true power divided by apparent power and expressed as a fraction.

The product of RMS voltage and RMS current in an AC circuit, measured in volt-amperes, combining both useful and reactive components of the load.

Power that oscillates between source and reactive load without doing useful work, measured in volt-amperes reactive and caused mainly by inductors and capacitors.

An AC supply of three voltages equal in magnitude and 120 electrical degrees apart, allowing balanced loads and constant total power delivery.

A three-phase connection joining one end of each winding at a neutral point, so line voltage is root-three times phase voltage and line current equals phase current.

A three-phase connection where windings form a closed loop, making line voltage equal phase voltage and line current root-three times phase current.

A material with low resistivity that carries electric current readily, such as copper or aluminium, used for wires, cables and busbars.

The resistance measured between a live conductor and earth or between conductors, showing whether insulation is healthy; tested with a megger at prescribed voltage.

Rigid or flexible polyvinyl chloride tube used to route and protect wiring in surface or concealed installations, resistant to moisture and most chemicals.

An installation method where insulated conductors are drawn through metal or PVC conduits for mechanical protection, easy replacement and neat appearance.

The minimum curve radius permitted when bending conduit or cable, set by the manufacturer or code so conductors are not damaged and can still be drawn through.

A twisted and soldered joint between two single conductors, made by crossing bare ends, twisting them tightly and finishing with solder and insulation.

A joint for two or more stranded conductors where bare ends are laid side by side, bound with a binding wire and soldered, then insulated.

Joining metals by melting a low-melting filler alloy between them; in electrical work a flux-cored solder and clean, tinned surfaces give a sound low-resistance joint.

Making a permanent electrical connection by compressing a metal lug or ferrule onto a conductor with a crimping tool, avoiding heat and giving a reliable joint.

A metal termination crimped or soldered onto a cable end so it can be bolted securely to a terminal, busbar or equipment stud.

A static device with two or more coupled windings that transfers AC power between voltage levels by electromagnetic induction, without changing frequency.

The ratio of primary to secondary winding turns, which sets the secondary voltage in proportion to the primary voltage for an ideal transformer.

Power lost as heat when circulating currents are induced in a transformer or machine core; reduced by laminating or using insulated core sheets.

Energy lost each AC cycle as the core magnetic material is repeatedly magnetised and demagnetised; reduced by choosing a low-loss core material.

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

The speed of the rotating magnetic field in an AC machine, equal to 120 times supply frequency divided by number of poles, in revolutions per minute.

An AC motor whose rotor current is induced by the rotating field of the stator, so no external connection to the rotor is needed.

An instrument that applies a high DC test voltage to measure insulation resistance in megohms, used to check cables, motors and installations before energising.

A check, usually with a low-voltage ohmmeter or buzzer, confirming that a circuit path is unbroken and that earth and bonding conductors are connected.

A combined measuring instrument selecting voltage, current, resistance and often continuity or diode ranges, with digital or analogue display.

A meter with a split core that clamps around a conductor and measures current by the magnetic field it produces, without breaking the circuit.

An instrument transformer whose primary carries the load current and whose secondary supplies a standard low current to meters and protection relays.

Deliberate connection of exposed metalwork or a circuit neutral point to the general mass of earth, giving a low-impedance path for fault current.

A buried metal rod, plate or strip making direct contact with soil to connect an installation to earth; its resistance depends on soil resistivity and moisture.

A measurement, typically by fall-of-potential or loop methods, of the resistance between an earth electrode and surrounding soil to confirm it meets the specified limit.

A protective device that trips when current leaking to earth through a fault exceeds its sensitivity, typically 30 milliamperes for personnel protection.

A resettable automatic switch that opens on overload or short circuit, rated by current and breaking capacity, used in distribution boards.

A protective device containing a metal element that melts and opens the circuit when current exceeds its rating for a defined time.

An unintended low-resistance path between live conductors or between live and earth, causing very large current flow and requiring fast disconnection.

A drawing using one line to represent all conductors of a circuit, showing supply, protective devices, distribution boards and loads in schematic form.

A drawing showing the physical connections and routing of conductors between components, used by the electrician to install and trace circuits.

A drawing using standard symbols to show the electrical function and logical arrangement of a circuit, without regard to physical position of components.

Calculating quantities of material, labour and time needed for an electrical installation from drawings and specifications before work begins.

An itemised schedule listing materials with description, unit and quantity, prepared from drawings so that costs can be priced consistently.

A priced offer submitted by a contractor to carry out specified electrical work according to drawings, specifications and conditions of contract.

A circuit, often using diodes, that converts alternating current into direct current; single-phase versions may be half-wave or full-wave bridge types.

A two-terminal semiconductor device that conducts readily in one direction and blocks the other, used for rectification, freewheeling and protection.

A four-layer semiconductor switch that conducts only after a gate pulse and turns off when current falls below holding level, widely used for power control.

A power electronic circuit that converts direct current into alternating current, often with adjustable frequency, for motor drives and backup supplies.

A controller that rectifies incoming AC, then inverts it at adjustable frequency and voltage to control the speed of an induction motor.

A device using thyristors or similar control to raise motor voltage gradually at starting, limiting inrush current and mechanical shock.

A series-wound motor that runs on either AC or DC, common in small appliances such as mixers and drills because of its high starting torque.

A single-phase induction motor with a capacitor in the starting winding to create high starting torque; the capacitor is switched out after run-up.

A temperature-actuated switch that opens or closes a circuit at preset temperatures, controlling heating elements in irons, geysers and ovens.

A resistive conductor, usually nichrome wire in a sheath, that converts electrical energy into heat in appliances such as irons, heaters and ovens.

Wearable safety gear such as insulated gloves, helmet, goggles and safety shoes that reduces injury risk during electrical work.

A procedure of isolating a supply, locking the isolator and attaching a warning tag so equipment cannot be re-energised while work is in progress.

A written authorisation specifying the isolation, safety precautions and duration for hazardous work, signed before the job starts and closed on completion.

The resistance within a source such as a cell or battery that causes its terminal voltage to fall as load current increases.