Pancyprian Electrical Engineering III (Practical) key terms

A recorded process that identifies hazards at a work location, judges who could be harmed and how, and sets out control measures before work begins. It must be reviewed when conditions change.

A written description of how a specific job will be carried out safely and in the correct sequence, naming the tools, personnel, and precautions needed. It accompanies the risk assessment for the task.

A formal written authorisation issued by a responsible person allowing defined work on specified equipment during a set period. It records isolation, earthing, and the hand-back procedure, and is cancelled when the work ends.

Fitting a personal lock and tag to an isolator, or to a lockable device over it, so that the circuit cannot be re-energised while someone is working on it. Only the person who applied the lock removes it.

The documented sequence for making an installation or circuit dead: identify the supply, isolate, lock off, prove the tester on a known source, prove the conductors dead, and re-prove the tester. It also covers warning notices and securing the point of isolation.

Confirming by measurement with an approved voltage indicator that all conductors of a circuit are at or near earth potential before touching them. The instrument must be proved before and after the test to show it works.

A two-pole or approved test lamp instrument used to detect the presence of voltage between conductors and to earth. It must be proved on a known live source or proving unit before and after use.

A portable source of a known safe test voltage used to confirm that a voltage indicator or test instrument is functioning correctly before and after proving a circuit dead.

Work on or near conductors that are, or may be, live. It is permitted only where it is unreasonable to make the installation dead and where additional precautions and authorisation are in place.

The relationship stating that current through a conductor equals the voltage across it divided by its resistance (I = U/R). It underpins every calculation of load current, voltage drop, and fault current in an installation.

The relationship for electrical power: P = U × I for direct current or purely resistive loads, with power factor included for alternating current. It is used to size circuits and to check protective device ratings.

The ratio of true power in watts to apparent power in volt-amperes for an alternating current circuit, equal to the cosine of the phase angle. It matters when calculating current for motors and other inductive loads.

The assumed factor by which the total connected load is reduced when sizing a supply or distribution board, because not all loads operate at full demand at the same time. It is applied using recognised diversity factors.

The greatest load, after applying diversity, that an installation or part of it is expected to draw. It determines the rating of the supply, main switch, and distribution board.

The reduction in voltage along a conductor caused by its impedance carrying load current. It is calculated from conductor length, current, and resistance or reactance and must stay within the permitted percentage of nominal voltage.

The total impedance of the path taken by fault current from the point of fault through the protective conductor, the earthing system, the supply transformer, and back through the line conductor. It must be low enough for the protective device to disconnect within the required time.

The current that would flow if a short circuit occurred at a given point in the installation, determined by the supply voltage and the impedance of the fault loop. Protective devices must be rated to break it safely.

The maximum fault current a protective device can safely interrupt without damage or danger. It must equal or exceed the prospective fault current at the point of installation.

The maximum permitted time for a protective device to clear a fault and disconnect the supply, set by the installation standard according to circuit type and nominal voltage. It is verified by comparing measured loop impedance with tabulated values.

Connecting exposed-conductive-parts and extraneous-conductive-parts to the installation earthing system so that fault current flows and a protective device operates, limiting touch voltage during the fault.

The connection of incoming metal services such as water, gas, and structural steel to the main earthing terminal, sized according to the supply neutral conductor. It limits potential differences within the installation.

The terminal or bar in an installation where the earthing conductor, circuit protective conductors, and main protective bonding conductors are connected together. It is the reference point for all earthing within the premises.

The conductor that connects exposed-conductive-parts of a circuit to the main earthing terminal, providing the return path for fault current. Its cross-sectional area is related to the line conductor size.

A protective device that trips when the difference between line and neutral current exceeds its rated residual operating current, detecting earth leakage. It provides additional protection against electric shock and fire.

An instrument test that applies a calibrated residual current to a device and measures the time it takes to trip, checked at half rated current, at rated current, and at five times rated current where required.

A residual current device test in which the applied residual current is increased gradually until the device operates, showing the actual operating current. It reveals a device that trips at too high or too low a level.

The coordination of protective devices so that the device nearest the fault operates first, leaving the rest of the installation energised. It is achieved by choosing ratings, types, and time-current characteristics that do not overlap.

A manually resettable overcurrent protective device with a thermal element for overload and a magnetic element for short circuit, marked with a rating and a tripping characteristic such as B, C, or D.

A protective device containing a fusible element that melts and breaks the circuit when current exceeds its rating for a given time. It has a defined breaking capacity and must be replaced after operation.

The assembly in a domestic or similar installation containing the main switch, protective devices, and often residual current devices, from which final circuits are supplied. It is the point where the installation is divided into circuits.

An enclosure containing protective devices and busbars that divides an incoming supply into sub-circuits or feeds other boards. It may include metering, switching, and control equipment.

The maximum sustained current a cable can carry without its conductor temperature exceeding the rated limit, given its size, insulation, installation method, and ambient conditions. It is adjusted by correction factors.

A multiplier applied to a tabulated cable rating to account for conditions such as ambient temperature, grouping of cables, thermal insulation, or burial depth that differ from the reference installation method.

A defined installation arrangement, such as clipped direct, in conduit, or buried, used in tables of cable current-carrying capacity. The actual installation method is matched to the nearest reference method.

A low-resistance measurement confirming that a conductor is electrically continuous end to end, carried out on protective conductors, ring final circuits, and bonding. Results are compared with expected values.

A measurement made with a high-voltage direct current instrument between live conductors and earth, and between live conductors, to confirm insulation is sound. Sensitive equipment is disconnected first.

A check that line, neutral, and protective conductors are connected in the correct positions at every point, including switches and socket outlets, so that single-pole devices are in the line conductor.

A certificate issued for small alterations or additions that do not include a new circuit, recording the extent of work, test results, and the declaration that the work complies with the regulations.

The certificate issued for new installations, rewires, or major alterations, containing the designer, installer, and inspector declarations plus schedules of inspections and test results.

The part of a certificate that records measured values for each circuit, including continuity, insulation resistance, polarity, earth fault loop impedance, and residual current device operation times.

The systematic process of locating a defect by gathering information from the user, testing logically through the circuit, and confirming the cause before repair. It avoids random replacement of parts.