gh-ctvet-cert-ii-electrical key terms

Clothing and gear such as insulated gloves, safety boots, arc-rated face shields and hard hats worn to reduce injury risk. It supplements, but never replaces, isolation, earthing and safe work procedures.

A procedure in which an energy source is switched off, physically locked, and tagged with the identity of the person working. It prevents unexpected re-energisation until the lock owner removes it.

The deliberate disconnection of all live conductors from every source of supply, including backup and control circuits, before work begins. Isolation must be verified by testing rather than assumed from switch position.

Confirming by test that conductors are at or near earth potential before touching them. The test is done with a proven voltage detector on the isolated conductors and repeated after testing the instrument itself.

A rapid release of heat and light caused by an electrical fault through air between conductors or to earth. It can ignite clothing and cause severe burns, so arc-rated clothing and safe approach distances are required.

The relationship stating that voltage equals current multiplied by resistance in a linear circuit at constant temperature. It allows any one quantity to be calculated when the other two are known.

The ratio of real power in watts to apparent power in volt-amperes in an alternating current circuit. A low value means more current flows for the same useful work, increasing losses and cable loading.

The total opposition to alternating current flow, combining resistance with inductive and capacitive reactance. It is measured in ohms and determines current for a given applied voltage.

An alternating supply of three voltages displaced by 120 electrical degrees, delivered over three line conductors and often a neutral. It provides constant power transfer and is standard for motors and distribution.

Two ways of connecting the windings of a three-phase machine or transformer. Star gives a higher voltage across each winding and a neutral point; delta gives no neutral and higher phase current.

The resistance measured between live conductors and earth, or between separate circuits, using a high test voltage. A low reading indicates moisture, damage or contamination and the circuit should not be energised.

A low-voltage check confirming that a conductor path is unbroken and has low resistance. It is used for protective conductors, ring final circuits and polarity checks with the supply isolated.

An instrument applying a high direct voltage, commonly 500 or 1000 volts, to measure insulation resistance in megohms. The circuit must be isolated and sensitive equipment disconnected before testing.

A meter whose jaws encircle a conductor to measure current through the magnetic field it produces, without breaking the circuit. It is useful for load surveys and fault finding on live equipment.

A portable instrument combining voltage, current, resistance and often continuity measurement in one unit. Correct range and function selection, plus a suitable safety category rating, are essential before use.

A device used to confirm the presence or absence of voltage on a conductor before work. Two-pole testers are preferred because they also prove the tester itself against a known source.

The maximum current a cable can carry continuously without its insulation exceeding its rated temperature. It depends on conductor size, insulation type, installation method, ambient temperature and grouping.

The reduction in voltage along a circuit caused by conductor resistance and reactance under load. Excessive drop causes dim lights and poor motor performance, so cable length and size must be checked.

A multiplier below one applied to a cable's tabulated current rating to account for conditions such as high ambient temperature, thermal insulation or several grouped circuits. It ensures the real installed rating is used.

A classification of how the supply neutral and installation exposed conductive parts are connected to earth. It determines which protective devices will operate and what fault loop impedance is acceptable.

The total impedance of the path taken by fault current from the point of fault back to the supply source. A low enough value ensures the protective device disconnects within the required time.

The resistance between an earth electrode and the general mass of earth, measured in ohms. It must be low enough for the earthing arrangement to limit touch voltage and allow protective operation.

Connecting exposed and extraneous conductive parts together so they sit at substantially the same potential. This limits touch voltage during a fault and is required in bathrooms and at the main earthing terminal.

A protective device that trips when the difference between line and neutral current, representing leakage to earth, exceeds its rated residual operating current. It protects people against earth faults.

Coordination of protective devices so that the device nearest a fault operates first, leaving the rest of the installation supplied. It is achieved by grading ratings, time settings and device types.

An automatically operated switch that opens on overload or short circuit and can be reset after the fault is cleared. Its tripping curve and breaking capacity must suit the circuit it protects.

An allowance recognising that not all connected loads operate at full power at the same time. Applying it avoids oversizing the supply and main protective device while keeping adequate capacity.

A drawing showing the electrical system with one line per circuit, including sources, switchgear, protective devices and ratings. It conveys the overall topology without showing every conductor or terminal.

A drawing that shows the electrical function and logical connections of a circuit rather than physical positions. Symbols are arranged for clarity, so it is used for fault finding and understanding operation.

A drawing showing the physical arrangement of components and the conductors between their terminals. It is used for assembly and connection, and its conductor numbering should match the equipment.

A table listing each cable's tag, type, size, number of cores, route and origin and destination. It supports procurement, installation and inspection, and must be updated to reflect as-built conditions.

A drawing revised to record the installation as actually constructed, including site changes and deviations. It is essential for future maintenance, fault finding and safe isolation.

A document describing how a task will be carried out safely, including sequence, plant, personnel, controls and emergency arrangements. It is usually supported by a risk assessment and signed off before work starts.

A structured evaluation of hazards, who may be harmed, the likelihood and severity of harm, and the controls needed. It must be recorded where significant risk remains and reviewed when conditions change.

A formal written authorisation controlling high-risk work such as live testing or work in confined spaces. It records isolation points, precautions, validity and the person authorising and receiving the work.

A formal record of the tests performed on an installation, with measured values compared against required limits. It is issued with the installation certificate and supports the declaration of conformity.

A written instruction authorising a change to the agreed scope, price or programme of a contract. It protects both parties by recording what changed and how it will be valued.

An itemised schedule of materials and work with quantities, used to price a tender and value progress. Accurate take-off from drawings is essential because omissions reduce profit.

A financial summary of revenue, direct costs and overheads over a period, showing gross and net profit. For a contractor it reveals whether labour, material and overhead recovery are adequate.

The timing of money entering and leaving a business. A profitable contractor can still fail if payments arrive after wages and suppliers fall due, so forecasting and retention release must be managed.